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Thursday, July 29, 2021

Task-Based Discrimination

AI Summary. The wage return to cognitive skills is higher for Black men than for White men in the same occupation and education, evidence the authors attribute to task-based discrimination. The authors estimate declining discrimination and narrowing skill gaps closed the racial wage gap by 8%, while rising returns to abstract tasks—where Black workers are underrepresented—widened it by 7%.

Erik Hurst National Bureau of Economic Research
Date Posted:
July 29, 2021
Is Database:
Database
Is Important:
Important

Research by @ErikHurst highlights task-based discrimination, where Black workers are underrepresented in high-paying Abstract tasks, widening the racial wage gap since 1980.

Does rising demand for abstract tasks offset declining racial discrimination in wages?

Core argument: Declining discrimination and narrowing racial skill gaps shrank the Black-White wage gap by 8% between 1980 and 2018, while the rising return to Abstract tasks widened it by 7%.

The wage return to cognitive skills is higher for Black men than for White men with the same occupation and education, highlighting task-based discrimination. Between 1980 and 2018, the racial wage gap narrowed by 8% due to declining discrimination and narrowing racial skill gaps. However, the increasing return to Abstract tasks widened the gap by 7%, disadvantaging Black workers who are underrepresented in these tasks. Despite declining race-specific barriers, the rising return to Abstract tasks has favored Whites since 1980, preventing Black-White wage convergence. The data from the U.S. Department of Labor's DOT and O*NET reveal that occupations demanding Abstract tasks, such as those requiring analytical flexibility and complex interpersonal communications, have seen increased returns, underscoring the systemic challenges Black workers face in achieving wage parity.

Takeaways by Macro Roundup® AI

  1. Declining discrimination and narrowing racial skill gaps shrank the Black-White wage gap by 8% between 1980 and 2018, while the rising return to Abstract tasks widened it by 7%.
  2. The wage return to cognitive skills is higher for Black men than for White men in the same occupation with the same education, a pattern characterized as task-based discrimination.
  3. Data from the U.S. Department of Labor's Dictionary of Occupational Titles and O*NET show rising returns to occupations demanding Abstract tasks such as analytical flexibility and complex interpersonal communication, in which Black workers are underrepresented.

Erik Hurst, Yona Rubinstein and Kazuatsu Shimizu, "Task-Based Discrimination," National Bureau Of Economic Research, July 2021, https://www.nber.org/papers/w29022

“…Manual: measures the degree to which the task demands eye, hand, and foot coordination. Occupations with high measures of Manual tasks include athletes, police and fire fighters, drivers (taxi, bus, truck), skilled construction (e.g, electricians, painters, carpenters) and landscapers/groundskeepers….”

“…Routine: measures the degree to which the task requires the precise attainment of set standards and/or repetitive manual tasks. Occupations with high measures of Routine tasks include secretaries, dental hygienists, bank tellers, machinists, textile sewing machine operators, dressmakers, x-ray technology specialists, meter readers, pilots, drafters, auto mechanics, and various manufacturing occupations….”

New Erik Hurst on the black-white wage gap finds that the narrowing of the wage gap btw black and white men prior to 1980 has been offset post 1980 by an increase in the returns to abstract tasks, "... the wage return to cognitive skills is higher for Black men than for White men with the same occupation and education. This is suggestive of the possibility that missing traits associated with Abstract tasks differ systematically between Black and White men…we find that the stagnation in the racial wage gap post-1980 is a product of two offsetting forces. On the one hand, a narrowing of racial skill gaps and declining discrimination between 1980 and 2018 caused the racial wage gap to narrow by 8 percentage points during this period, all else equal. On the other hand,the changing returns to tasks since 1980 - particularly the increasing return to Abstract tasks - widened the racial wage gap by about 7 percentage points during the same period. A rise in the return to Abstract tasks disadvantages Black workers because they are underrepresented in these tasks due to a combination of racial skill gaps and discrimination. In sum, the estimated model highlights that race-specific barriers have continued to decline in the U.S. economy post-1980 but the rising relative return to Abstract tasks has favored Whites since 1980. As a result, the Black progress stemming from narrowing racial skill gaps and/or declining discrimination did not translate into Black-White wage convergence during this period. On the other hand, we show that the relative wage gains of Black men relative to White men during the 1960 to 1980 period stemmed solely from declining discrimination and a narrowing of racial skill gaps; changing task prices did not undermine any of these gains during this earlier period...."

Task-Based Discrimination: Extended Excerpt Image 1


The data, "...we measure the skill demands in each occupation using the following data: (i) the U.S. Department of Labor’s Dictionary of Occupational Titles (DOT) and (ii) the Occupational Information Network (O*NET) sponsored by the U.S. Department of Labor/Employment and Training Administration (USDOL/ETA). The DOT was constructed in 1939 to help employment offices match job seekers with job openings. It provides information on the skills demanded in over 12,000 occupations. The DOT was updated in 1949, 1964, 1977, and 1991, and replaced by the O*NET in 1998. We focus on four occupational task measures that are relevant for our study: Abstract, Routine, Manual and Contact...."

The four measures:

“…Abstract: indicates the degree to which the occupation (i) demands analytical flexibility, creativity, reasoning, and generalized problem-solving and (ii) requires complex interpersonal communications such as persuading, selling, and managing others. Occupations with high measures of Abstract tasks include accountants, software developers, high school teachers, college professors, judges, various medical professionals, engineers, and managers...”

Ed Comment:That outcome seems at odds with the study which says there is discrimination against blacks in abstract/conceptual jobs. Ben, how does it reconcile? Is there an appendix that shows the wages of black and whites vs their relevant abstract/conceptual credentials? They mention AFQT test scores but don't seem to use them. Do they use them? Does the appendix show wages vs test scores (and other credentials), which they clearly seems to have? Using education as a measure of intelligence is problematic because blacks are admitted to colleges with substantially lower scores. Let's read and summarize the reference Neal (decker) 2006, which accompanies their claim that blacks in abstract jobs are paid more than whites. I glanced at it. It's pretty direct. It says: "Some may argue that what matters is not realized returns to investments but rather the fact that many blacks believe that the labor market will not reward them or their children for investing in human capital. The literature on statistical discrimination began with Arrow (1973) and Phelps (1972). When Arrow and Phelps first developed these ideas, existing cohorts of adult workers had lived most of their lives in labor markets where blacks may well have earned lower returns to education and skills than whites workers.28 However, it is hard to find data that would support this belief today. Blacks who reached adulthood after the Civil Rights Act of 1964 have not earned systematically lower returns to attainment or achievement than their white peers. During the past decade or more, black adult respondents in the NLSY79 have earned relatively high returns to skills measured by the AFQT.29 Further, as I demonstrate below, apparent returns to formal schooling among black young adults have typically been as large or larger than the corresponding returns among whites since at least 1970....In the balance of this section, I present details concerning the relationship between education and labor market outcomes among black and white adult men. Existing panel data sets do not provide information concerning racial differences in the relationship between cognitive skills and adult outcomes for birth cohorts other than those included in the NLSY79.30 However, census data document the relationship between educational attainment and labor market outcomes for a broad range of cohorts. Education differs from reading and math scores in that it is an indirect measure of skill that is easily observed by employers, but the patterns documented below are similar to those in Figures 4(a)-5(b). Correlations between schooling and positive labor market outcomes among blacks are as strong or stronger than the corresponding correlations among whites, especially in recent decades. 30 The National Educational Longitudinal Surveys provide panel data on high school experiences and adult labor market outcomes. However, these samples are drawn from students who are enrolled in specific grades at a point in time, and thus they provide select samples from persons born in a set of birth years. In addition, the follow-up data on earnings and employment are of relatively poor quality in the NELS surveys when compared to NLSY79 on work outcomes...." Has he updated this or related work? Has he written anything else of high interest? Maybe I'll talk to him at U Chicago.

Ben Comment:From the paper: "The differences in pre-labor market skills and discrimination facing Black workers give rise to differential sorting into tasks between Black and White individuals in the spirit of Roy (1951). These sorting differences need to be accounted for in order to parse out the effects of race-neutral driving forces (such as time trends in task specific returns) and race-specific driving forces (such as a narrowing of racial skill gaps and/or declining discrimination) when explaining changes in racial wage gaps over time. Using the model structure and empirical moments on the differential occupational sorting of Black and White men, the changing returns to various tasks, and the evolution of the aggregate racial wage gap, we estimate the key driving forces of the model.” Most black people are kept out of the abstract jobs because of discrimination/skill differences (below I pull a quote where they say these skill differences are the result of discrimination, too). The only black people who move into the abstract job categories are the ones who have overcome these. If you think in terms of diminishing marginal productivity, only the absolutely most productive black workers are in the “abstract” category, so they’re making higher wages than the average. If more black people entered abstract jobs, they would bring down the average productivity and (presumably) the wage. The issue of discrimination has to do with the number (or proportion) of black people who enter the field, not with what they make conditional on entering the field. From the discussion of figure 4: "Most of the racial gaps in the average task returns are slightly negative suggesting that the task return to Black men are systematically smaller than White men of similar age and education.” So it’s only in “abstract” tasks that we see a “premium” paid to black workers. And according to this graph it’s very small. Additionally, in the model section: "First, the average skill level may differ across race groups stemming from current or past discrimination.” The assumption is that skill differences are because of discrimination and are not “genetic”. I didn’t see any graphs in the appendix like the ones you asked about.
Ed Comment:I’m still confused (about the math). (I don’t care what the paper says about the causes of racial difference in test scores. The authors are not experts in that. That’s obligatory BS to cover their asses. …and let’s not debate it. It would help my understanding of the paper if you ignored your hypotheses and focused on what the data and the math in the paper actually measure and the limitation of those measures. My own view, from a lot of experience hiring people into highly analytical jobs, is that there is great demand and competition between employers for scarce analytical blacks because of societal demands. Like colleges, we greatly lowered the bar. And their chances of success were far greater as a result of these allowances. So I’m not surprised blacks are paid more than whites in analytical jobs, with the premium growing larger the more precisely they can measure the true analytical capacity of the person and the extent to which the job demands analytical capability.) I don’t see how they measure the extent to which selection bias improves the pool of workers relative to their credentials. I would think they merely have their wage, some measure of the pedigree of their analytical credentials, and measures of the extent to which the job they perform is analytical. If not, please explain. What measures do they use for the pedigree of their analytical credentials? How do they measure the extent to which the job is analytical? My guess is that unless they are using their AFQT score—something the most analytical people are unlikely to have—they don’t have a measure of the analytical skill beyond yes/no. What measure of analytical prowess do they use? Similarly, is the analyticalness of the job measured or is it just yes/no? If it’s measured, how so? Are they merely saying, black people in analytical positions get paid more than white people in analytical positions, on average, without regards to measures of the person’s or the job’s anlysiticalness? Or are they making some adjustment for the extent to which the job is analytical and for the pedigree of the person’s analytical credentials? If black people are paid more than whites on average in analytics jobs, how do they measure discrimination in analytical jobs? I don’t see how the math works or could work unless the measurements are quite precise. For example, they could say black people in analytical jobs have test scores of 125, whereas white people in analytical jobs only have test scores of 115. Blacks are paid more than whites, but, given their higher test scores, they should be paid even more than they are being paid. Show me if and how they do that. If they have all these measures and wages, I’d love to see a graph of x - measure of analyticalness (e.g., test score), and y - wages for blacks vs whites. Again, let’s not speculate about what the data means. Let’s focus on the data they have and how they use it to calculate how people who are paid more are discriminated against.
Ben Comment:They do not create the graph “ x - measure of analyticalness (e.g., test score), and y - wages for blacks vs whites”. Looking at the BLS website it seems like that might be something we can do (it’ll take time, I don’t know these data at all). Other questions below, without my commentary - all language is drawn from the paper. ED: How do they measure the extent to which the job is analytical? "we measure the skill demands in each occupation using the following data: (i) the U.S. Department of Labor’s Dictionary of Occupational Titles (DOT) and (ii) the Occupational Information Network (O*NET) sponsored by the U.S. Department of Labor/Employment and Training Administration (USDOL/ETA) … The first three measures are taken exactly from Autor and Dorn (2013) and Deming (2017) using the DOT data. Below, we provide a brief summary of these measures. The last task measure is new and was created specifically for this paper to help get at the concept of taste-based discrimination. Building on the work in Deming (2017), Contact measures the extent to which an occupation requires interaction and communication with others within the organization (co-workers) or outside the organization (customers/clients) …
Abstract: indicates the degree to which the occupation (i) demands analytical flexibility, creativity, reasoning, and generalized problem-solving and (ii) requires complex interpersonal communications such as persuading, selling, and managing others. Occupations with high measures of Abstract tasks include accountants, software developers, high school teachers, college professors, judges, various medical professionals, engineers, and managers. Routine: measures the degree to which the task requires the precise attainment of set standards and/or repetitive manual tasks. Occupations with high measures of Routine tasks include secretaries, dental hygienists, bank tellers, machinists, textile sewing machine operators, dressmakers, x-ray technology specialists, meter readers, pilots, drafters, auto mechanics, and various manufacturing occupations. Manual: measures the degree to which the task demands eye, hand, and foot coordi- nation. Occupations with high measures of Manual tasks include athletes, police and fire fighters, drivers (taxi, bus, truck), skilled construction (e.g, electricians, painters, carpenters) and landscapers/groundskeepers. Contact: measures the extent that the job requires the worker to interact and communi- cate with others (i) within the organization or (ii) with external customers/clients or potential customers/clients. To create our measure of Contact tasks we use two 1998 O*NET work activity variables taken from Deming (2017). Specifically, we use the variables Job-Required SocialInteraction(Interact)andDealWithExternalCustomers(Customer).4 Interactmea- sures how much workers are required to be in contact with others in order to perform the job. Customer measures how much workers have to deal with either external customers (e.g., retail sales) or the public in general (e.g., police work). To make our measure of the Contact task content of an occupation, we take the simple average of Interact and Customer for each occupation. Occupations with high measures of Contact tasks include various health care workers, waiter/waitress, sales clerks, lawyers, various teachers, and various managers." Appendix A.3 has even more detail and Autor and Dorn (2013) and Deming (2017) have even more detail if you’d like us to find that for you. ED: What measures do they use for the pedigree of their analytical credentials/What measure of analytical prowess do they use? From the ACS: "In most specifications, we control for the worker’s age and accumulated years of schooling.” From the NYSL: "The NLSY data allows us to link a worker’s subsequent occu- pational choice with pre-labor market measures of cognitive, non-cognitive, and social skills… The key reason we use the NLSY data is to have measures of racial differences in pre- labor market skills. We use measures of performance on cognitive test and psychometric assessments to generate a set of unified proxies for cognitive, non-cognitive and social traits across the two NLSY waves. These skill measures were primarily collected before the indi- viduals entered the labor market. Again, our goal is to take these skill measures directly from the existing literature. We summarize these measures briefly here and include a more detailed discussion in the online appendix. Cognitive Skills (COG): We follow the literature and use the respondent’s standard- ized scores on the Armed Forces Qualifying Test (AFQT) as our measure of cognitive skills. The AFQT is a standardized test which is designed to measure an individual’s math, verbal and analytical aptitude. The test score was collected from all respondents in their initial year of the survey and was measured in both the 1979 and 1997 waves.7 Non-cognitive Skills (NCOG): We use the measures of non-cognitive skills created by Deming (2017). Deming (2017) uses questions pertaining to the Rotter Locus of Control Scale and the Rosenberg Self-Esteem Scale for the NLSY79 cohort to make a measure of non- cognitive skills.8 Likewise, for the NLSY97 cohort Deming (2017) uses respondent answers (provided prior to entering the labor market) to the question “How much do you feel that conscientious describes you as a person?” to approximate respondents’ non-cognitive skill. Deming (2017)’s non-cognitive skill measures are expressed in z-score units. Social Skills (SOC): We again follow Deming (2017) to generate a unified measure of social skills using a standardized composite of two variables that measure extroversion in both waves. Specifically, for the NLSY79, we use self-reported measures of sociability in childhood and sociability in adulthood. Individuals were asked to assess their current sociability (extremely shy, somewhat shy, somewhat outgoing, or extremely outgoing) and to retrospectively report their sociability when they were age 6. For the NLSY97, we proxy for social skills using the two questions that were asked to capture the extroversion factor from the commonly-used Big 5 personality inventory. For each wave, we normalize the two questions so they have the same scale and then average them together. We then convert the measures into z-score units. Deming (2017) shows that these measures of social skills positively predict individual wages when they are adults even conditional on controlling for individual measures of cognitive skills (AFQT).” ED: are they making some adjustment for the extent to which the job is analytical and for the pedigree of the person’s analytical credentials?

Task-Based Discrimination: Comments Image 1


"wijt is the log wage of individual i working in occupation j during year t. Our coefficients of interest are again the βg ’s, the Mincerian wage premium of task k in year t kt for group g. For this regression, we use are sample of full-time workers… the demographically adjusted Black-White gaps in the wage premium by task requirement (Panel B) … Finally, the racial gaps in the wage premiums to tasks are relatively small and roughly constant over time. Most of the racial gaps in the average task returns are slightly negative suggesting that the task return to Black men are systematically smaller than White men of similar age and education”. ED: If black people are paid more than whites on average in analytics jobs, how do they measure discrimination in analytical jobs? "New to our model is differential returns to performing each type of tasks across different race groups. We allow for three forces that can cause the returns to tasks to differ across races. First, the average skill level may differ across race groups stemming from current or past discrimination.16 We capture this by writing the skill endowment vector as Φgi = {ηgk +φi1.., ηgK +φiK }, where ηgk represents the skill (or human capital) level of group g associated with task k. Second, workers of a particular race group may face taste-based discrimination in performing a task. Taste-based discrimination may exist if for example customers do not like interacting with Black employees or White workers do not like interacting with their Black co-workers. In the presence of taste-based discrimination, we assume that employers perceive the efficiency of the discriminated workers to be δtaste+ηgk+φik rather than ηgk+φik, gk where δtaste is the race-specific taste-based discrimination coefficient in task k. Thus, the gk potential log wages of a worker belonging to race g becomes:

Task-Based Discrimination: Comments Image 2


Lastly, workers may face statistical (rather than taste-based) discrimination if their employers do not perfectly observe individual workers’ skills. If skills are observed with noise, employers form expectations about a worker’s marginal product by using information about the individual’s group. The statistical discrimination coefficient, δstat, will therefore differ gk by task based on underlying gaps in group mean of skills (ηgkt’s) used to perform the task. We formally incorporate the notion of statistical discrimination into the model by intro- ducing noise to skill measurement. Suppose employers cannot observe worker’s true efficiency, ηgk + φik, and instead only observe a noisy skill measure given by where the noise εik is drawn from a normal distribution with mean zero and variance σ2 (common to all race groups). Employers, however, observe a worker’s group affiliation and know the underlying distributions of ηgk + φik and εik. In this environment, employers set the wage of each worker at the worker’s expected marginal revenue product conditional on observed skills (sˆi1..,sˆik) and the worker’s group affiliation… In sum, our task-based model of discrimination predicts differential sorting patterns across race groups as group-specific forces such as discrimination and racial skill differences make the task returns differ by group.”

“…Contact: measures the extent that the job requires the worker to interact and communicate with others (i) within the organization or (ii) with external customers/clients or potential customers/clients. To create our measure of Contact tasks we use two 1998 O*NET work activity variables taken from Deming (2017). Specifically, we use the variables Job-Required Social Interaction (Interact) and Deal With External Customers (Customer). 4 Interact measures how much workers are required to be in contact with others in order to perform the job. Customer measures how much workers have to deal with either external customers (e.g., retail sales) or the public in general (e.g., police work). To make our measure of the Contact task content of an occupation, we take the simple average of Interact and Customer for each occupation. Occupations with high measures of Contact tasks include various health care workers, waiter/waitress, sales clerks, lawyers, various teachers, and various managers….”

"... Figure 1 shows the difference in log wages between Black and White workers conditional on age and education using our sample of Census/ACS individuals. In particular, for each year, we regress an individual’s log hourly wage on a race dummy and controls of age (fiveyear age dummies) and series of dummies indicating the individual’s accumulated level of education. Consistent with other findings in the literature, the demographically adjusted racial wage gap narrowed substantially between 1960 and 1980 but has been constant at a gap of roughly 20 log points since 1980.5 Our goal is to explain both the wage convergence in Figure 1 between 1960 and 1980 as well as its stagnation post-1980..."

Task-Based Discrimination: Comments Image 3


Skills measure

“..Cognitive Skills (COG): We follow the literature and use the respondent’s standardized scores on the Armed Forces Qualifying Test (AFQT) as our measure of cognitive skills. The AFQT is a standardized test which is designed to measure an individual’s math, verbal and analytical aptitude. The test score was collected from all respondents in their initial year of the survey and was measured in both the 1979 and 1997 waves….”

“…Non-cognitive Skills (NCOG): We use the measures of non-cognitive skills created by Deming (2017). Deming (2017) uses questions pertaining to the Rotter Locus of Control Scale and the Rosenberg Self-Esteem Scale for the NLSY79 cohort to make a measure of noncognitive skills.8 Likewise, for the NLSY97 cohort Deming (2017) uses respondent answers (provided prior to entering the labor market) to the question “How much do you feel that conscientious describes you as a person?” to approximate respondents’ non-cognitive skill. Deming (2017)’s non-cognitive skill measures are expressed in z-score units….”

“…Social Skills (SOC): We again follow Deming (2017) to generate a unified measure of social skills using a standardized composite of two variables that measure extroversion in both waves. Specifically, for the NLSY79, we use self-reported measures of sociability in childhood and sociability in adulthood. Individuals were asked to assess their current sociability (extremely shy, somewhat shy, somewhat outgoing, or extremely outgoing) and to retrospectively report their sociability when they were age 6. For the NLSY97, we proxy for social skills using the two questions that were asked to capture the extroversion factor from the commonly-used Big 5 personality inventory. For each wave, we normalize the two questions so they have the same scale and then average them together. We then convert the measures into z-score units. Deming (2017) shows that these measures of social skills positively predict individual wages when they are adults even conditional on controlling for individual measures of cognitive skills (AFQT)….”

“…in Figure 2. Panels A and B, respectively, show the patterns excluding and including the vector… of demographic controls. The main take-away from the figure is that both the level difference in racial task gaps in 1960 and the subsequent time series trend differ markedly by task. The differences are especially pronounced when we compare the racial gaps in Abstract and Contact tasks.In the early 1960s, Black workers were systematically underrepresented both in occupations that required a high intensity of Abstract tasks and in occupations that required a high intensity of Contact tasks. In terms of magnitudes, in 1960 a one-standard deviation increase in the Abstract task contents of an occupation reduced the probability that an individual working in that occupation was Black by about 3 percentage points, and a one-standard deviation increase in the Contact task contents reduced the probability that the individual was Black by about 4 percentage points, both conditional on education. Over the last half a century, however, Black men have made significant progress relative to White men with respect to sorting into occupations that require Contact tasks, while they made no progress relative to White men in the extent to which they sort into occupations that require Abstract tasks.Whereas the racial gap in Abstract tasks remained essentially constant through 2000 and widened slightly after 2000, the large racial gap in Contact tasks that existed in 1960 has all but disappeared by 2018. This finding persists whether or not we control for individual age and education (Panel A vs. Panel B), although the level of the Abstract task gap narrows once we control for them. If discrimination took the form of co-workers and customers not wanting to interact with Black workers in 1960, the patterns in Figure 2 are consistent with that form of discrimination abating over time.10 Although we focus on such differences to a lesser extent, there were only small racial differences in the propensity for Black and White men to work in occupations that require Manual tasks. Likewise, there was some convergence in the propensity to work in occupations that require Routine tasks between 1960 and 1980, but large racial gaps still remain post-1980….”

Task-Based Discrimination: Comments Image 4


“…Figure 4 reports estimates of the raw wage premium by task requirement for White men (Panel A) and the demographically adjusted Black-White gaps in the wage premium by task requirement (Panel B). Three main findings emerge from this figure. First, the average wage premium of Abstract tasks for White men was between 10 and 15 percent higher than the return to the other tasks in 1960. Moreover, the relative return of Abstract tasks has been increasing since 1980. This increase in the return to Abstract tasks has received lots of attention in the literature (Autor and Dorn (2013), Deming (2017)). Second, in contrast, the wage premium associated with Contact tasks was notably lower in the early 1960s and has not changed much since then. Finally, the racial gaps in the wage premiums to tasks are relatively small and roughly constant over time. Most of the racial gaps in the average task returns are slightly negative suggesting that the task return to Black men are systematically smaller than White men of similar age and education….”

Task-Based Discrimination: Comments Image 5


“…The results are shown in Table 1. Each column comes from a separate regression projecting an individual’s cognitive, non-cognitive or social skills on the relative task content of the occupation in which they work...Table 1 highlights that individual skill supplies respond differentially to relative task demands. Workers with higher cognitive skills are more likely to match with jobs that require higher Abstract tasks and workers with higher social skills are more likely to match with jobs that require higher Contact tasks. For example, occupations where their relative Abstract task requirement is one-standard deviation higher attract workers who score approximately 0.2 standard deviations higher on cognitive tests. Occupations where their Contact tasks requirement is one-standard deviation higher attract workers whose social score is 0.08 standard deviation higher. The results in this table highlight that the NLSY skill measures are informative about the types of jobs into which individuals sort. Having shown that the occupational task measures are associated with particular NLSY skill measures within the sample of White men, we now explore differences in pre-labor market skills between Black and White men within the NLSY cohorts.13 Table 2 reports the racial gap in cognitive, non-cognitive, and social skills with various controls for the two separate NLSY samples. The first column for each sample includes all NLSY respondents in the sample without conditioning on employment; each of these samples has only one NLSY respondent per regression. The remaining columns pool over all years and only include individuals that were working. The second column within each sample adds no further controls, while the third column controls for the individual’s maximum level of education and the last column controls also for their occupation The main takeaway from this table is that the racial gap in cognitive skills is large and narrows over time (especially for working men), whereas the gaps in non-cognitive and social skills are relatively small and constant over time. As seen from Table 2, Black men from the NLSY79 have AFQT scores that are 1.20 standard deviations lower than White men from the NLSY79 cohort. The gap declines to 0.93 when we additionally control for racial education and occupation differences. The race gap in AFQT scores narrowed somewhat between the NLSY79 and NLSY97 cohorts but was still large at -0.58 standard deviations conditional on education and occupation in the later period. On the other hand, the racial skill gaps in non-cognitive and social skills conditional on education and occupation were close to zero for both NLSY cohorts….”

Task-Based Discrimination: Comments Image 6


"... Once we control for the rising return to cognitive skills over time, however, we find a strong convergence in racial wage gaps post 1980. Specifically, in column 3, we control for time-varying return to just cognitive skills. In this column, we find a narrowing of the racial wage gap relative to the 1980s of about 4 log points in the 1990s, about 9 log points in the 2000s, and about 10 log points in the 2010s. The results are nearly identical when we additionally control for time-varying returns to non-cognitive and social skills (column 4).27 As suggested by our model, conditioning out the effects of time-varying skill returns - the rising return to cognitive skills in particular - unveils the convergence in the racial wage gap due to changing race-specific factors. Strikingly, the magnitude of the convergence we estimate in the NLSY between 1980 and 2018 once properly controlling for the changing returns to skills (column 4 of Table 4) is close to the magnitude we estimate from our structural model(Panel B of Figure 7)..."

Task-Based Discrimination: Comments Image 7


Good factoid in table four, "... the wage return to cognitive skills is higher for Black men than for White men with the same occupation and education...." implies higher skilled black men see a wage premium.

"... First, in Table 4 above, we exploit the panel structure of the NLSY and show that controlling for unmeasured traits by including individual fixed effects hardly affects the estimated changes in the racial wage gap over time (compare columns 1 and 2 of Table 4). This suggests that omitted skills play little role in the evolution of the racial wage gap over the last forty years. Second, in the appendix, we examine whether the labor market returns to skills differ between Black and White men in the NLSY. We find that the labor market returns to social skills are similar between Black and White men. This finding is consistent with there being no differential bias between Black and White men with respect to predicting Contact task efficiency from measured traits. On the other hand, consistent with the findings in Neal (2006), the wage return to cognitive skills is higher for Black men than for White men with the same occupation and education. This is suggestive of the possibility that missing traits associated with Abstract tasks differ systematically between Black and White men...."

Task-Based Discrimination: Comments Image 8


Bottomline"...There are two important results highlighted in the paper. First, our paper provides an explanation for both why the Black-White wage gap narrowed between the 1960s and 1970s and why the racial wage gap has remained constant thereafter. We find that the constant wage gap between Black and White men post-1980 is due to two offsetting effects. Both the racial skill gap narrowed and taste-based discrimination fell post-1980 resulting in the wages of Black men converging to those of White men, all else equal. However, during the same period, the return to Abstract skills rose disadvantaging Blacks relative to Whites. This latter effect resulted in increasing racial wage gaps during the 1980-2018 period. The magnitude of these two effects were roughly similar resulting in a relatively constant racial wage gap post-1980. On the other hand, we show that the relative wage gains of Black men relative to White men during the 1960 to 1980 period stemmed solely from declining discrimination and a narrowing of racial skill gaps; changing task prices did not undermine any of these gains during this earlier period. We also provide a road map to empirical researchers looking to uncover changing race specific factors in micro data. Second, our paper establishes that the declining racial gap in Contact tasks between 1960 and 2018 is a good proxy for declining taste-based discrimination during this period.We motivated the introduction of this novel task measure by conjecturing ex-ante that occupations which require many interactions with others are more likely to be susceptible to taste-based discrimination; our model and data work confirm this conjecture ex-post. Specifically, the fact that there are very small racial gaps in social skills - combined with the fact that measures of pre-labor market social skills in the NLSY are highly predictive of subsequent entry into occupations that require Contact tasks - implies that racial gaps in Contact tasks must stem almost entirely from taste-based discrimination and very little from racial skill differences or statistical discrimination. Our model thus implies that the changes in racial gaps in Contact tasks over time is a good proxy for taste-based discrimination. To further provide evidence for this conclusion, we document that state-level racial gaps in Contact tasks correlate strongly with state-level survey measures of taste-based discrimination, while state-level racial gaps in Abstract tasks correlate with them only weakly….”

Ed Comment:I read the paper, so I read the definitions. I was looking for your explanation of what they were measuring after you read the paper, not theirs. after reading the paper, (and these snippets) it was unclear to me, and I was uncertain about what data they were truly using/measuring. Experience has taught me that people often say they did (or measured) X when they did something other than what they said they did. Sometimes they exaggerate. Sometimes they don’t fully understand what they did. Often, they assume they did X because they believe they did X or hoped to do X. In their equation, which variable is the AFQT test score? …or years of schooling? Is years of schooling their measure of analytical capability? I still don’t understand how blacks are discriminated against in analytical tasks when they are paid more on average of analytical tasks. (Are they paid more on average? That was unclear.) Blacks would have to have higher scores/more years of schooling or perform a mix of more analytical (more higher paid tasks). Which is it? My life experience is that the scores are lower on average. They are paid more for lower scores because high scoring blacks are highly sought after. But they may be paid less than higher scorers performing the same job. So I wouldn’t think the above would not be the case, i.e., blacks do not have higher scores on average or more analytical jobs. So I’m looking for your description for what the math in the study says in this regard. How does the study account for this?

Ben Comment:Ok, let me try again: ED: How do they measure the extent to which the job is analytical? First they take an occupation’s title (economist, researcher, scientist, burger flipper, etc.) and look up that occupation in DOT/O*NET. DOT/ONET matches an occupation’s title with the types of tasks that occupation performs and what skills are needed to perform them Firms are surveyed to see how much of a particular task is required of a particular occupation (the results have different scales so they’re harmonized). Then these tasks are classified into the 4 categories - by Autor & Dorn in the cases of Abstract, Routine, Manual and by Demings in the case of Contact. They determine which jobs are analytical by asking businesses which jobs require analytical tasks. NOTE - occupation is a control. The paper is about *tasks* and *skills*. So they merge DOT/ONET with ACS on occupation and regress wages onto the tasks/skills necessary. ED: What measures do they use for the pedigree of their analytical credentials/What measure of analytical prowess do they use? In the sections that examine the ACS, they’re using years of schooling. That’s section 3.1. In equation (1) on pg 12, the years of schooling is in X_(it) and is a control variable. They then move onto the NLSY data in section 3.2 (pg 16). These data are more robust in terms of demographic detail but also have a smaller sample. There are 2 waves of the NLSY - 79 and 97. In Appendix A.2, they explain both waves include the AFQT score. In general, you’re right, highly analytical people are unlikely to have taken this. In this particular case, however, everyone in the survey took it. Participants are chosen at random to participate in the survey. As far as I understand, once in the survey, everyone is given this test. Now, it’s true, surveys are likely to miss top top performers but this methodology does not suffer from the same selection bias using just military enrollment would. They also exclude observations with missing scores and reweight the entries. Section 6.3 is where they start using the NYSL for wage regressions: Equation 9 on pg 34. In this equation, one of the S^(NYLS)_(ki)’s is cognitive ability, and one of the variables in X_(it) is education. This regression specification does NOT interact race with cognitive ability so we are looking at the difference in wages of blacks/whites controlling for cognitive ability. Table A1 in appendix E shows the coefficient for black * Cognitive - and it’s positive. They also show the model imputed skills black*abstract (panel B) and that’s positive as well. The abstract skill variable, however, is a model implied variable constructed in section 7. To construct the variable, they take the average of the tasks done by each race. This is a complicated procedure to describe in words but the equations are on page 36+37. Essentially, they regress the occupational-average of observed task specific skills for whites (model generated) onto the average skill levels for whites observed in the NYSL. They then use the estimated white-black skills gap (table 1 pg 17) to impute the racial gaps in the task-specific skills in each occupation. Note: They do not show an explicit regression equation for this table but do explain the controls in the footnotes. I think I’ve covered the different measures of skills and how they’re used. ED: are they making some adjustment for the extent to which the job is analytical and for the pedigree of the person’s analytical credentials? They are NOT making adjustments for pedigree of institutions. They do control for years of education. However - they’re using actual pre-college test scores in their regressions or using those test scores to impute skills, so it’s unclear what the pedigree of the institution adds - especially if you believe those test scores are highly correlated with the pedigree of the institutions. ED: If black people are paid more than whites on average in analytics jobs, how do they measure discrimination in analytical jobs? They are interested in 2 types of discrimination, taste based and statistical. Taste based means - we don’t like black people. Statistical means - if a boss cannot perfectly observe a person’s analytical ability, they default to that person’s group’s mean of ability. This means, for smart blacks, if ability is noisy, they are assumed to have the average level of black intelligence and therefore earn lower wages. This type of discrimination is laid out in section 4, pg 22, the paragraph towards the bottom starting with “Conceptually, it would be useful to see the statical discrimination term ….” Essentially, if there is noise in determining someone’s analytical skill, they’re assumed to have the average and this discriminates against smart blacks. ED: In their equation, which variable is the AFQT test score? …or years of schooling? Is years of schooling their measure of analytical capability? I think I answered which variables are which above, but let me know if it’s still unclear. Their measure of analytical capabilities is the actual AFQT test score in the data. They ALSO include years of schooling as a control. ED: I still don’t understand how blacks are discriminated against in analytical tasks when they are paid more on average of analytical tasks. (Are they paid more on average? That was unclear.) Blacks would have to have higher scores/more years of schooling or perform a mix of more analytical (more higher paid tasks). Which is it? Blacks, on average, are paid less than whites (figure 1). Figure 1 was created with the ACS data so does NOT have the intelligence controls. Figure 4 breaks out the racial wage gap in terms of tasks. This graph, again, is created using the ACS data and does not include controls for tests scores. Figure 5 Panel A shows the model predicted racial wage gap. It’s model generated (not data) but also shows blacks, even smart ones, earning less. They do not have a break out of wages vs test scores from the NYSL like you’re describing. (This is where editorializing has to come in, sorry): As for the discrimination - remember regressions are holding all else equal. So what those positive coefficients mean is: Holding all else equal (occupation, wage, education, and ALL OTHER SKILLS), and increase in intelligence for a black guy will raise his wages more than the same sized increase in intelligence for a white guy. But the discrimination can come from all sorts of other things - like the occupations they have access to or the schooling they have access to or any number of other things. Additionally, if a white and a black guy have similar wages, conclusion of the paper says it’s likely the black guy is more skillful in Contact/Routine (tasks) or in Social/non-cognitive skills than the white guy; so raising his intelligence makes him *more* skillful than his white counterpart.

  • Test Scores
  • Comparisons
    • Race
    • Skill Level
  • Workforce
    • Education
    • Wages/Income

Monday, August 9, 2021

U.N. climate panel confronts implausibly hot forecasts of future warming

AI Summary. Many scientists judge the warming rates in recent climate models implausibly fast, and the Intergovernmental Panel on Climate Change plans to constrain model projections using observed warming from recent decades, potentially cutting uncertainty by 50% and lowering extreme projections. A worst-case 2100 projection could fall from 5°C to 4.2°C above 1986-2005 levels.

Paul Voosen Science
Date Posted:
August 9, 2021
Is Database:
Database

Revamp of climate change models as current models are projecting rates that are implausibly fast. The IPCC plans to use actual warming data to constrain CMIP projections, potentially reducing uncertainty by 50% and lowering extreme projections.

Are climate models projecting warming faster than observations support?

Core argument: The IPCC plans to constrain CMIP projections with observed warming from recent decades, an approach that could cut uncertainty by 50% and lower a worst-case 2100 projection from 5°C to 4.2°C above 1986–2005 levels.

Recent climate models have projected warming rates that many scientists deem implausibly fast, prompting a reevaluation of these models. The IPCC [Intergovernmental Panel on Climate Change] plans to use actual warming data from recent decades to constrain CMIP [Coupled Model Intercomparison Project] projections, potentially reducing uncertainty by 50% and lowering extreme projections. For instance, a worst-case scenario for 2100 could see projected warming reduced from 5°C to 4.2°C above 1986-2005 levels. This recalibration is crucial for policymakers and financial institutions that rely on these models to assess economic impacts and the true cost of carbon emissions. The need for more accurate models is underscored by the fact that global warming has progressed enough to provide clearer observational data, which can guide future projections and policy decisions.

Takeaways by Macro Roundup® AI

  1. The IPCC plans to constrain CMIP projections with observed warming from recent decades, an approach that could cut uncertainty by 50% and lower a worst-case 2100 projection from 5°C to 4.2°C above 1986–2005 levels.
  2. Many scientists deem the warming rates projected by recent climate models implausibly fast, prompting a reevaluation of those models.
  3. Policymakers and financial institutions rely on these climate models to assess economic impacts and the cost of carbon emissions.

“…"...the climate models that help them project the future have grown a little too alarmist. Many of the world’s leading models are now projecting warming rates that most scientists, including the modelmakers themselves, believe are implausibly fast. In advance of the U.N. report, scientists have scrambled to understand what went wrong and how to turn the models, which in other respects are more powerful and trustworthy than their predecessors, into useful guidance for policymakers. “It’s become clear over the last year or so that we can’t avoid this,” says Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies... So the IPCC team will probably use reality—the actual warming of the world over the past few decades—to constrain the CMIP projections. Several papers have shown how doing so can reduce the uncertainty of the model projections by half, and lower their most extreme projections. For 2100, in a worst-case scenario, that would reduce a raw 5°C of projected warming over 1986-2005 levels to 4.2°C...."

Paul Voosen, "U.N. climate panel confronts implausibly hot forecasts of future warming,"Science, July 27, 2021, https://www.sciencemag.org/news/2021/07/un-climate-panel-confronts-implausibly-hot-forecasts-future-warming

U.N. climate panel confronts implausibly hot forecasts of future warming

Next month, after a yearlong delay because of the pandemic, the U.N. Intergovernmental Panel on Climate Change (IPCC) will begin to release its first major assessment of human-caused global warming since 2013. The report, the first part of which will appear on 9 August, will drop on a world that has starkly changed in 8 years, warming by more than 0.3°C to nearly 1.3°C above preindustrial levels. Weather has grown more severe, seas are measurably higher, and mountain glaciers and polar ice have shrunk sharply. And after years of limited action, many countries, pushed by a concerned public and corporations, seem willing to curb their carbon emissions.

But as climate scientists face this alarming reality, the climate models that help them project the future have grown a little too alarmist. Many of the world’s leading models are now projecting warming rates that most scientists, including the modelmakers themselves, believe are implausibly fast. In advance of the U.N. report, scientists have scrambled to understand what went wrong and how to turn the models, which in other respects are more powerful and trustworthy than their predecessors, into useful guidance for policymakers. “It’s become clear over the last year or so that we can’t avoid this,” says Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies.

Ahead of each major IPCC report, the world’s climate modeling centers run a set of scenarios for the future, calculating how different global emissions paths will alter the climate. These raw results, compiled in the Coupled Model Intercomparison Project (CMIP), then feed directly into the IPCC report. The results live on as other scientists use them to assess the impacts of climate change, insurance companies and financial institutions forecast effects on economies and infrastructure, and economists calculate the true cost of carbon emissions, says Jean-François Lamarque, a lead climate modeler at the National Center for Atmospheric Research (NCAR) and CMIP’s new director. “This is not an ivory tower type of exercise.”

In the past, most models projected a “climate sensitivity”—the warming expected when atmospheric carbon dioxide (CO2) is doubled over preindustrial times—of between 2°C and 4.5°C. Last year, a landmark paper that largely eschewed models and instead used documented factors including ongoing warming trends calculated a likely climate sensitivity of between 2.6°C and 3.9°C. But many of the new models from leading centers showed warming of more than 5°C—uncomfortably outside these bounds.

The models were also out of step with records of past climate. For example, scientists used the new model from NCAR to simulate the coldest point of the most recent ice age, 20,000 years ago. Extensive paleoclimate records suggest Earth cooled nearly 6°C compared with preindustrial times, but the model, fed with low ice age CO2 levels, had temperatures plummeting by nearly twice that much, suggesting it was far too sensitive to the ups and downs of CO2. “That is clearly outside the range of what the geological data indicate,” says Jessica Tierney, a paleoclimatologist at the University of Arizona and a co-author of the work, which appeared in Geophysical Research Letters. “It’s totally out there.”

To find out why, modelers probed the guts of the simulations, focusing on their representation of clouds, long the wild card of climate change. The models can’t simulate clouds directly, so they rely on known physics and observations to estimate cloud properties and behavior. In previous models ice crystals made up more of the low clouds in the midlatitudes of the southern Pacific Ocean and elsewhere than satellite observations seemed to justify. Ice crystals reflect less sunlight than water droplets, so as these clouds heated and the ice melted, they became more reflective and caused cooling. The new models start with more realistic clouds containing more supercooled water, which allows other dynamics driven by warming—the penetration of dry air from above and a subduing of turbulence—to thin the clouds.

But that fix has allowed scientists to spy another bias previously countered by the faulty cooling trend. In both the old and new climate models, the patchy cumulus clouds that form in the tropics thin out in response to warming, allowing in more heat than satellite observations suggest, according to a study by Timothy Myers, a cloud scientist at Lawrence Livermore National Laboratory. “Even though one feature of the climate is now more realistic, another that’s persistently biased has been revealed,” Myers says.

U.N. climate panel confronts implausibly hot forecasts of future warming: Extended Excerpt Image 1


By the time modelers exposed that bias, the supercomputing runs were already done and the IPCC report was nearing completion. And many of the hot models otherwise simulate the climate extremely well overall, doing a better job than their predecessors at capturing atmospheric connections between remote ocean basins and the distribution of rainfall. “You want a way you can use those models for what they have without getting stuck with their climate sensitivity,” Schmidt says.

So the IPCC team will probably use reality—the actual warming of the world over the past few decades—to constrain the CMIP projections. Several papers have shown how doing so can reduce the uncertainty of the model projections by half, and lower their most extreme projections. For 2100, in a worst-case scenario, that would reduce a raw 5°C of projected warming over preindustrial levels to 4.2°C. It’s good news for the modelers—but also a clear, and dismaying, sign that global warming has gone on long enough to help chart its own path, says Aurélien Ribes, a climate scientist at France’s National Centre for Meteorological Research. “Observations now provide a clear view for what climate change will be.”

The IPCC report is also likely to present the spatial impacts of different amounts of warming—2°C, 3°C, 4°C—rather than saying how quickly those impacts will be felt. That heat-based technique worked well in an interim IPCC report in 2018, on the impacts of 1.5°C of warming, and would preserve good information from the hot models, even if they suggest these thresholds will come too soon.

The modelers hope to do better next time around. Lamarque says they may test new simulations against recent paleoclimates, not just historical warming, while building them. He also suggests that the development process could benefit from more time, with updates every decade or so rather than the current report interval of every 7 years. And it could be helpful to divide the modeling process in two, with one track focused on scientific experimentation—when a large range of climate sensitivities is helpful—and the other on providing a best estimate to policymakers. “It’s not easy to reconcile these two approaches under a single entity,” Lamarque says.

A cadre of researchers dedicated to the task of translating the models into useful projections could also help, says Angeline Pendergrass, a climate scientist at Cornell University who helped develop one technique for weighting the model results by their accuracy and independence. “It’s an actual job to go between the basic science and the tools I’m messing around with,” she says.

For now, policymakers and other researchers need to avoid putting too much stock in the unconstrained extreme warming the latest models predict, says Claudia Tebaldi, a climate scientist at Pacific Northwest National Laboratory and one of the leaders of CMIP’s climate projections. Getting that message out will be a challenge. “These issues don’t translate very well in practice,” she says. “It’s going to be hard for people looking to make some projection of a water basin in the West to make sense of it.”

Already scientific papers are appearing using CMIP’s unconstrained worst-case scenarios for 2100, adding fire to what are already well-justified fears. But that practice needs to change, Schmidt says. “You end up with numbers for even the near-term that are insanely scary—and wrong.”

  • Global Warming
  • Science

Mating Contests Among Females, Long Ignored, May Shape Evolution

AI Summary. Research finds females across species including sea urchins and salamanders are subject to sexual selection, though less intensely than males, with positive Bateman gradients—indicating a fitness gain from multiple matings—in 72 species. Studies of male-male competition and female choice have been 10x more prevalent than studies of female competition.

Jake Buehler Quanta Magazine
Date Posted:
August 9, 2021
Is Database:
Database

Recent research highlights that females across various species are subject to sexual selection, albeit less intensely than males. This finding challenges traditional views & suggests that female sexual selection could significantly influence evolutionary forces.

Recent research highlights that females across various species are subject to sexual selection, albeit less intensely than...

Are females also shaped by sexual selection across many species?

Core argument: Bateman gradients were positive for females in 72 species, indicating a fitness gain from multiple matings and suggesting that sexual selection in females is more common than previously thought.

Recent research highlights that females across various species, including sea urchins and salamanders, are subject to sexual selection, albeit less intensely than males. This finding challenges traditional views and suggests that female sexual selection could significantly influence evolutionary forces. Historically, studies of male-male competition and female choice have been 10 times more prevalent than those focusing on female competition. The study utilized Bateman gradients to quantify sexual selection, revealing positive gradients for females in 72 species, indicating a fitness boost from multiple matings. This suggests that sexual selection in females is more common than previously thought, potentially impacting evolutionary dynamics and necessitating a reevaluation of female roles in sexual selection.

Takeaways by Macro Roundup® AI

  1. Bateman gradients were positive for females in 72 species, indicating a fitness gain from multiple matings and suggesting that sexual selection in females is more common than previously thought.
  2. Females across species including sea urchins and salamanders are subject to sexual selection, though less intensely than males, a finding that challenges traditional views of female roles in sexual selection.
  3. Studies of male-male competition and female choice have been 10 times more prevalent than those focusing on female competition, which researchers argue warrants a reevaluation of female sexual selection.

"... A study hosted on the preprint server biorxiv.org has found that in animals as diverse as sea urchins and salamanders, females are subject to sexual selection — not as harshly as males are, but enough to make biologists rethink the balance of evolutionary forces shaping species in their accounts of the history of life.The new work turns a spotlight on a lopsidedness in sexual selection research that may have robbed evolutionary studies on about half of all animal species of important context. Scientists have reported scattered evidence of female sexual selection in the past, but more often they haven’t had reason to look for it. That could now be changing...."

Jake Buehler, "Mating Contests Among Females, Long Ignored, May Shape Evolution,"Quanta Magazine, August 2, 2021, https://www.quantamagazine.org/mating-contests-among-females-may-shape-their-evolution-20210802/

Mating Contests Among Females, Long Ignored, May Shape Evolution

As the midday sun hangs over the Scandinavian spruce forest, a swarm of hopeful suitors takes to the air. They are dance flies, and it is time to attract a mate. Zigzagging and twirling, the flies show off their wide, darkened wings and feathery leg scales. They inflate their abdomens like balloons, making themselves look bigger and more appealing to a potential partner.

Suddenly, the swarm electrifies with excitement at the arrival of a new fly, the one they have all been waiting for: a male. It’s time for the preening flock of females to shine.

The flies are flipping the classic drama reenacted across the animal kingdom, in which eager males with dazzling plumage, snarls of antlers or other extraordinary traits compete for a chance to woo a reluctant female. Such competitions between males for the favor of choosy females are enshrined in evolutionary theory as “sexual selection,” with the females’ choices molding the evolution of the males’ instruments of seduction over generations.

Yet it’s becoming clear that this traditional picture of sexual selection is woefully incomplete. Dramatic and obvious reversals of the selection scenario, like that of the dance flies, aren’t often observed in nature, but recent research suggests that throughout the tree of animal life, females jockey for the attention of males far more than was believed. A study hosted on the preprint server biorxiv.org has found that in animals as diverse as sea urchins and salamanders, females are subject to sexual selection — not as harshly as males are, but enough to make biologists rethink the balance of evolutionary forces shaping species in their accounts of the history of life.

The new work turns a spotlight on a lopsidedness in sexual selection research that may have robbed evolutionary studies on about half of all animal species of important context. Scientists have reported scattered evidence of female sexual selection in the past, but more often they haven’t had reason to look for it. That could now be changing.

“We really don’t know very much compared to how much we’ve worked on the male side of things,” said Tommaso Pizzari, an evolutionary biologist at the University of Oxford who was not involved with the new paper. “Sexual selection in females is still relatively unknown. It’s still barely charted territory.”

The concept of sexual selection dates back to Charles Darwin’s first writings on natural selection — briefly mentioned in The Origin of Species, and then covered more extensively in The Descent of Man — where he detailed reproductive preferences between the sexes as potentially driving evolutionary change. Within the framework of conventional natural selection, it makes sense that individuals prefer fit mates. But a key point of sexual selection is that attractiveness to potential mates can be a criterion for selection in itself, independently of how it affects fitness otherwise. Members of one sex can develop traits and behaviors appealing to the other that directly conflict with survival-driven natural selection. Taken to extremes, this can result in the unwieldy, exceptionally elongated display feathers of some male birds, for example, which are only useful in the mating contests that the males stage.

The Victorian View of Females

Yet from its very beginning, the science focused on males as the objects of sexual selection. Darwin saw females as reluctantly picking mates from gaggles of desperate male suitors. He was open to the idea of sexual selection in either direction, but the intensity of the obvious competitions for mates among males fed the idea that sexual selection happened primarily to males; the females were prizes to be won. Females might be setting the terms of the mating competitions, but it was the males who were truly being reshaped through evolution by those choices.

Darwin’s perspective was typical of his time. Theories about sexual selection were born “in the Victorian era, when you had these certain sexual stereotypes about how women should behave,” said Rebecca Boulton, an evolutionary biologist at the University of Exeter in the U.K. “And so, because the field essentially sprung up at that time, it was like, ‘Of course females aren’t mating with multiple males. Of course they’re coy or choosy.”

This viewpoint has contributed to a ubiquitous bias in how sexual selection has been investigated in the last century and a half, the researchers behind the new study argue. They estimate that studies of male-male competition and the phenomenon of female choice are 10 times more common than studies targeting the reverse.

“A lot of people are influenced by the culture that they live in and the things that see,” said Salomé Fromonteil, a graduate student in evolutionary biology now at Uppsala University in Sweden and Ludwig Maximilian University in Munich, and lead author on the study. “It’s influenced by what we read, and what they read is that sexual selection works on males primarily.”

There are undeniable exceptions. Some that have caught researchers’ attention are in species with “sex roles” that are flipped from the conventional arrangement, as in the dance flies. Females of the American tropical wading birds called wattled jacanas (Jacana jacana) keep and defend territories rich in male mates. Among the seahorses and other pipefish, males even take on the job of “pregnancy” by internally incubating their young in a specialized pouch.

Still, scientists studying sexual selection have mostly continued to defer to Darwin’s initial observations in the 19th century. It was generally accepted that males — with their propensity for ornaments and courtship displays — experienced greater sexual selection pressures.

“Of course, that’s not how research should be,” said Tim Janicke, an evolutionary biologist at the Center for Functional and Evolutionary Ecology at the University of Montpellier in France, and senior author of the new study. “If the aim is to describe general patterns in nature, we need data-driven syntheses behind this.”

In 2016, Janicke and his team dove into the published literature measuring the strength of sexual selection acting on a variety of animal species and compared those values between the sexes. That study, published in Science Advances, confirmed that males experience a higher degree of sexual selection than females did.

But as further examples of species likely to be undergoing female sexual selection accumulated, Janicke and his team were struck by a question that their study had not addressed: Just how common is sexual selection among females? They began to wonder whether it was “something rare, or whether it’s actually a general pattern,” Janicke said.

In early 2020, Janicke and Fromonteil were planning to start an empirical study on sexual selection in beetles to probe that question. Then the COVID-19 pandemic and the institutional shutdowns it triggered made laboratory experiments suddenly infeasible. But a meta-analysis of the data from the 2016 study could be done even in “confinement,” as Janicke puts it.

To compare the relative strength of sexual selection in a wide range of species, the scientists needed some way of quantifying that selection intensity. They settled on a method using the Bateman gradient, a measurement named after the 20th-century British geneticist Angus John Bateman.

More Mates, More Sexual Selection

Bateman recognized that while males can produce many sperm at low metabolic cost, females have to make relatively high investments in far fewer eggs. In the 1940s, his research on fruit flies led Bateman to propose that this fundamental divergence in gamete investment drives apart the mating strategies of males and females: To maximize their reproductive capacity, males might routinely seek out and compete for many mating partners, while females might instead evolve to be choosy.

Other researchers built on this idea, developing the Bateman gradient to describe the fitness benefits of having multiple mating partners. The measurement is the slope of the line comparing reproductive output to the number of mating events — in effect, it shows how sharply an organism’s number of offspring increases with more mating. The steeper the positive slope, the greater the fitness benefit of more mating events, which in most species means having more mates. (By mating with multiple males rather than just one, a female can sometimes hedge her bets about which mate will produce the fittest offspring.)

“If there’s positive selection on having more mating partners, this should translate into competition for mating partners,” said Janicke. “And this competition is basically the essence of Darwinian sexual selection.” For this reason, Bateman gradients are a common way of indirectly quantifying sexual selection.

From a sweep of the scientific literature, the team compiled 111 Bateman gradients calculated for females in 72 animal species, ranging from beetles to mollusks to mammals. The gradients varied widely, but they clustered in the positive range. The team also found, as expected, that species with “polyandrous” females who had access to many partners simultaneously had Bateman gradient values considerably greater than those of species with “monandrous” females who mostly mated with one male at a time.

The findings suggest that — as has long been presumed for males — females get a fitness boost from multiple matings, and that opens the door to widespread sexual selection. The positive female Bateman gradients don’t appear to be as large as those for males, Janicke said, but their pervasiveness hints at the importance of sexual selection in the evolution of females, even in species seen as having “typical” sex roles.

While acknowledging that the Bateman gradient is a “powerful measurement to quantify sexual selection,” Janicke noted that it only reflects selection directly related to the act of mating. In species that spawn profusions of eggs, such as many fish as well as corals and other marine invertebrates, there are opportunities for selection after mating, too, with eggs competing for access to sperm, or sperm having choice capabilities that affect fertilization. Janicke’s study did not extend to this kind of post-mating sexual selection. It’s therefore possible that even more female sexual selection occurs than the new study suggests, but future work will need to test that possibility.

For Pizzari, the study “confirms something that I think we have been, as a community, beginning to realize for quite some time now: that sexual selection is potentially quite important in females across a number of species, as well as for males.”

Alternative explanations, however, do still need to be tested. Some of the gradients that Janicke’s team identified may be rooted in certain females’ inherent attractiveness to males due to their reproductive output. “It may well be that the females that have more eggs to produce … happen to attract a lot more males simply because they have a higher reproductive value,” Pizzari said. If so, it wouldn’t be that more matings were more beneficial to females, “it’s that males are more interested in mating with fecund females.”

If that is the case, however, then Jonathan Henshaw, an evolutionary biologist at the University of Freiburg in Germany who was also not involved with the study, thinks that empirical tests could help isolate this effect. “If you really wanted to know what the causal effect of mating on reproductive success is, the best thing would be to do as others have done and actually manipulate the number of mates that are available to individual females,” he said.

Experiments could also help reveal whether sexual selection is playing out in these females in the wild, and how selection might be influencing the traits that females use to compete with one another. “The potential for … different mechanisms of sexual selection is there,” Boulton said. “Whether that’s what’s actually happening is something that is a little bit harder to tease apart.”

Confrontations and Decorations

Now that scientists are becoming more aware that they should look for evidence of female sexual selection, the traits and behaviors it cultivates in females may become more obvious. Black grouse (Tetrao tetrix) were considered a classic example of male sexual selection: The males have distinct, vivid coloration, and they compete for females in elaborate courtship display arenas called leks. But recent evidence suggests that while the males are putting on their show, the females are also aggressively jockeying for their choices. Female Mediterranean fruit flies (Ceratitis capitata) take a very similar approach. Certain dung beetle females have even evolved horns that may be used for battling with other females in contests over access to males.

But such intrasexual combat isn’t likely to develop in most females, Boulton argues. Fighting has an inherent risk of bodily harm — something that males can more easily afford since they just need to survive until copulation. Female reproductive success takes time: They have to live long enough to lay all their eggs, and sometimes to care for the newborns. “Whereas the males, they’ve kind of got less to lose,” she said.

The ornaments and competitions that females use to gain mates may sometimes have been overlooked because they are more subtle and look like pared-down versions of what males sport. For instance, female Malurus fairy wrens are undergoing sexual selection on their bill and plumage coloration independently of similar pressures on the males. Both male and female chickens (Gallus gallus) have fleshy ornamental combs. Hens prefer roosters with bigger combs as mates, but the roosters give more sperm to hens with bigger combs, too.

Such ornamentation traits in females are sometimes viewed as byproducts of sexual selection on a female’s male ancestors — “leaky sexual dimorphism,” Pizzari said. But he argues that males may pay attention to these ornaments, which could give them evolutionary significance in the females. “They might have been the target of adaptive selection in their own right.”

Another trait that males commonly seem to key in on is female body size, Boulton said. Males tend to prefer bigger and heavier females. This preference might be rooted in the value of size as a signal of the females’ overall health and reproductive potential, but it could also be a platform for female competitiveness.

No matter how female animals respond to sexual selection in nature, the new findings help reiterate how much of it went largely undetected by science for many decades. Part of the rigid stereotyping around research into sexual selection was likely informed by culture and patriarchal attitudes.

The stereotype of male-centered sexual selection may also have persisted so stubbornly “because there’s a kernel of truth in it — that in the vast majority of species, males do gain more from additional matings than females do,” Henshaw said. The pitfall is that “it’s sort of easy to go from that truth to an opposite stereotype which says that ‘generally speaking, females don’t gain anything from extra matings.’ But then you’ve kind of gone too far.”

Extreme physical differences between the sexes in some species may also have blunted the search for the more hidden but widespread sexual selection among females. “If you have a species that shows this striking sexual dimorphism, you might not start to study intrasexual selection among females,” Janicke said, because male selection would seem like the default explanation.

And yet, despite the weight of human assumptions and sensory biases, a pattern is beginning to rise to the surface: Female sexual selection is the norm. “Generally speaking, sexual selection operates on females,” Fromonteil said.

Janicke plans to continuously update the database with Bateman gradients as they are published. “This database will grow and grow, and we’ll see what other kinds of questions we can still address with this. But I am very confident that this pattern on sexual selection for females will not change,” he said.

  • Evolution/Heredity
  • Science


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