stabilizing selection in humans

Most of this work has focused on searching the genome for signatures of past selective events (1). "Stabilizing Selection in Evolution." 3 shows r^g,rLRS for the subset of traits for which an estimate was marginally significant (P ≤10−3) in at least one sex. This can happen by various mechanisms, in particular, when the heterozygotes for the alleles under consideration have a higher fitness than the homozygote. All genetic variance and covariance estimates are contained in Dataset S2. In addition, the genetic correlations are estimated using common SNP markers (minor allele frequency > 0.01), which may be a source of bias because the genetic variants with deleterious effects on fitness are likely to be rare and thus absent from our analyses. Scoville, H. (2013). Based on the first and third quartile values of γ^, we estimate that a reasonable range for human phenotypes is VSVP∼28−173 with a median of 65, which would be considered weak, but nontrivial in a theoretical context (9). In males, the estimates of β for hand-grip strength, pulse rate, body-mass index (BMI), and systolic blood pressure are significant in the multiple regression and retain their direction of association from the single-trait regression models. Stabilizing Selection – A selective force that pushed a population towards the middle of a trait spectrum. This is despite the fact that people with higher EA tend to have fewer children overall and is consistent with prior work in the Icelandic population (27). (19) found a negative genetic correlation between relative lifetime reproductive success (rLRS)—the individual lifetime reproductive success divided by the mean—and age at first birth, using a bivariate linear mixed-modeling approach (26, 29). This approach was not computationally feasible on the full dataset; we report the results on the full dataset using LD-score regression in the main text, but see SI Appendix for a discussion of the LMM results. However, the evidence is less clear when we compare the results on AFB to other female reproductive life-history traits such as the age at menarche (AAM) and age at menopause (AMP). Copyright © 2021 National Academy of Sciences. Such weak selection gradients are unlikely to lead to large changes in phenotypic distributions over clinically or socially relevant timescales (25, 27). Consistent with previous studies, our results support a hypothesis of strong negative selection on female AFB (14⇓⇓⇓⇓–19, 51⇓⇓–54). Combining high-throughput molecular genetic data with extensive phenotyping enables the direct study of natural selection in humans. This analysis was supported by the observation that rLRS had a low, but measurable heritability. Selective pressures are environmental factors that lead to directional selection. A multiple-regression analysis provided a more conservative perspective on the phenotypic correlates of rLRS. The dataset consists of over 500,000 individuals from the United Kingdom who have been genotyped at common SNPs and clinically phenotyped for many different traits. selective force or forces which push a population toward the average Linear and quadratic selection gradients were converted into parameters of a Gaussian fitness function. Phenotypic evidence suggests that stabilizing selection, which acts to reduce variance in the population without necessarily modifying the population mean, is widespread and relatively weak in comparison with estimates from other species. However, the direction of the association between EA and rLRS in females is positive in the multiple-regression setting. However, many of these traits are highly correlated (SI Appendix, Figs. doi: 10.1073/pnas.1806837115. Birth weight is a classic example of a trait under strong stabilizing selection, where high and low birth weights are correlated with reduced survival in both males and females (22). 2 further illustrates that the predicted phenotypic optimum is above and below the population mean height for males and females, respectively, consistent with multiple previous studies showing a difference in contemporary selection pressures on height between males and females (13). The new study found many traits such as height under 'stabilizing' selection. While important differences between the studied populations exist (12, 13), a few interesting trends have emerged. It favors the major phenotype in a population that is well adapted to the environment. Stabilizing selectionhappens when extreme phenotypes on both ends of the spectrum are unfavorable. If the birth weight of a human is too low, it will have difficulty surviving after birth. Our work supports further study of a dynamic moving-optimum model for the evolution of complex traits in humans. Because of possible heterogeneity in selection pressures and rLRS measurement precision—documented number of live births in females vs. self-reported number of children fathered in males—all analyses were performed on a sex-specific basis. We also observed a small but positive relationship between AMP in females and rLRS on the phenotypic level, which agrees with previous results (11, 14, 17, 54). Scoville, Heather. Overall, the data are indicative of a moving optimum model for contemporary evolution of human quantitative traits. In addition, the interaction term between EA and AFB is strongly positive (βAFB:EA^=0.03±0.0016(P<10−112)). The most common model of stabilizing selection used in evolutionary quantitative genetics is the Gaussian stabilizing selection model (56). (A and B) Scatterplot showing the magnitude of (A) linear selection gradients β^ and (B) quadratic selection gradients γ^ for a selection of traits in females and males. S1B shows a skew toward negative values. This implies that there is some sex-specific selection acting on these phenotypes, consistent with recent work on the genetic and phenotypic correlates of viability (45). While selection acts on phenotypes, evolution requires genetic variation. Do high-status people really have fewer children? VI. The genetic covariance between a phenotype and fitness determines the expected evolutionary change (2⇓–4) of that phenotype in a population. For example, the direction of association between female EA and rLRS is positive in the multiple regression, which opposes results from our single-trait regressions, genetic correlation analyses, and multiple other published results (16, 25, 27, 48⇓–50). Wollstein A(1), Stephan W(1). Contemporary directional and stabilizing selection. designed research; J.S.S. However, Beauchamp (25) noted that the bivariate analyses are underpowered with modest sample sizes and chose to analyze genetic predictors derived from the results of independent large genome-wide association studies (GWAS). We find no traits with significant γ^ in both sexes with opposite signs. ThoughtCo. Recall that we estimated a significant negative selection gradient in females with a small but significant positive selection gradient in males. Fig. Additionally, the data suggest that the relationship between rLRS and height is more negative in females than in males, which agrees with other results in the literature (18, 24, 25). However, the positive genetic correlation between rLRS and AAM is less explicable. Rather, it appears that correlated factors, such as AFB, drive the apparent selection (46) on EA. Stabilizing selection is a type of natural selection in which the population mean stabilizes on a particular non-extreme trait value. There are several classic examples in animals and humans of the results of stabilizing selection process: Heather Scoville is a former medical researcher and current high school science teacher who writes science curriculum for online science courses. Phenotypes are the physical features of animals and humans. Stabilizing Selection in Evolution. Towards the end of the stabilizing component. Multiple studies have suggested that directional selection has acted to lower the age at first birth in females (14⇓⇓⇓⇓–19), increase the age at menopause (14, 17), increase weight in females (17, 18, 20), and decrease height in females (13, 17, 18, 20, 21) in contemporary postindustrial populations. Natural selection in populations. Therefore, the relationships between phenotypes and fitness must be studied in contemporary populations to observe natural selection directly. A) Humans with close to the average birth weight are more likely to survive than humans with very large or very small birth weights. This material is based upon work supported by the National Science Foundation (NSF) Graduate Research Fellowship Program under Grant DGE-1321846. A number of articles enlist the pandemic to study basic questions about financial investment, education, politics, learning, crime, and other aspects of social life. Thank you for your interest in spreading the word on PNAS. When multiple traits interact to create a combined phenotype, correlational selection may be an important process driving adaptive evolution. Fig. (2020, August 27). Although the genetic result for females did not pass our study-wise significance threshold, the results are consistent with the hypothesis that contemporary selection on reproduction favors higher BMI in males and support exploration of the same hypothesis in females. Height is the only trait we studied for which the data indicate sexually antagonistic selection. is greater for those either under- or over-weight, and that the mean birth weight (7 lbs) coincides with that showing minimum mortality. In doing so, we can gain insights about the direction and magnitude of phenotypic evolution. 8.10 Z&E The phenotypic results are in agreement with prior studies in Western populations (13), suggesting that selection on reproductive success favors shorter females and taller males. Direct evidence for the action of stabilizing selection in humans is scarcer. In fact, we estimate that the genetic correlation with rLRS is positive for AAM (r^g,rLRS = 0.133±0.032(P<10−4.4)) and negative for AMP (r^g,rLRS = −0.168±0.045(P<10−3.7)). First, we apply the Lande and Arnold (10) framework through regression analyses of the relationship between a suite of phenotypes and a proxy for fitness, rLRS, in 217,728 females and 158,638 males. However, our results for AFB are more indicative of a plateauing of directional selection toward the upper phenotypic extreme rather than true disruptive selection (SI Appendix, Fig. This issue can be partially mitigated by accounting for population structure (28) and geography in samples of unrelated individuals. Meaning and Causes of Stabilizing Selection. Levels of variation in three skeletal regions (pelvic canal, noncanal pelvis, and limbs) of females and males are compared to each other and between sexes. Stabilizing selection (also called balancing selection) is thus acting on the sickle-cell allele: (1) Selection tends to eliminate the sickle-cell allele because of its lethal effects on homozygous individuals, and (2) selection tends to favor the sicklecell allele because it protects heterozygotes from malaria. This stands in sharp contrast to the separate regression results and strongly points away from a simple linear relationship between EA and increased rLRS. In these scenarios, the middle ranges are the optimal birth rate.The size of a clutch of eggs that birds lay is limited to a certain amount of eggs that helps guarantee maximum survival rates. Further, the empirical relationship between LRS and height, illustrated in SI Appendix, Fig. There are a few other important caveats and limitations to our present analyses. There are many examples of stabilizing selection that have to do with organisms’ sizes. Phenotypic selection in natural populations: What limits directional selection? Additionally, phenotypic evidence has been presented that is indicative of the simultaneous action of directional and stabilizing selection on height in the Dutch (24). Phenotypes may also be subject to stabilizing selection or disruptive selection, which are both nonlinear forms of selection. The estimates of γ were much less significant in the multiple regression compared with the separate regressions. In technical terms, stabilizing selection discards the extreme phenotypes and instead favors the majority of the population that is well adapted to their local environment. S19). These insights support ongoing efforts to use theoretical evolutionary models to understand the maintenance of heritable variation for complex traits in humans (5⇓⇓⇓–9, 34⇓⇓⇓⇓⇓⇓⇓⇓–43). However, because we see no evidence for a genetic correlation between height and rLRS in males, we do not predict that the observed phenotypic selection in males would induce a response to selection (in a single generation). The result of stabilizing is the over-representation in a specific trait. Genetic drift, bottleneck effect, and founder effect. In this type of selection, species are usually stay the same and show little change. Stabilizing selecton occurs when genetic diversity declines and as a result, the population mean value stabilizes for a specific trait. In the first attempt to use SNP-array data to study contemporary natural selection on complex traits, Tropf et al. Better understanding the tradeoffs presented by different bioplastics should help elucidate which options, if any, are viable replacements over the long run. When rainfall, and thus food, are plentiful, the ground finches tend to 1. have a varied diet, e.g., eat seeds of a range of sizes; 2. show considerable variation in body and beak … Stabilizing selection commonly uses negative selection to select against extreme values of the character. This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1707227114/-/DCSupplemental. This fact has led to considerable interest in understanding how natural selection and other evolutionary forces combined to shape the allelic spectrum underlying variation within and between populations. The stabilizing process is one that results statistically in an over-represented norm. Birth weight is one reported example of a human trait under stabilizing selection (22), although the intensity of selection has decreased in postindustrial societies (23). However, a recent study in the contemporary United States found no evidence for any nonlinear selection (25)—although sample size may have limited the power to detect such effects. Population genetics. A plant that is too short may not be able to compete with other plants for sunlight. 1A. S3). Image credit: ScienceSource/Jean-Michel Labat. Scoville, Heather. Variation in a species. Here we report observational evidence that is consistent with the action of natural selection in a contemporary human population. The results suggest that many traits measured in the UKB are under the influence of directional and stabilizing selection. Direct evidence for the action of stabilizing selection in humans is scarcer. Phenotypic analyses were performed using linear regression in R (57). It's more or less a bell curve, with mostly intermediate phenotypes but also some extreme phenotypes at both ends of the spectrum. 1B shows that among traits with significant γ^ in both sexes the male estimate tends to be farther from zero (with height being an exception). However, this does not mean that all individuals are exactly the same. Here, we analyze the phenotypic and genetic correlates of rLRS in the UK Biobank (UKB). "Stabilizing Selection in Evolution." Evolution – When selection acts on a population over time, changing the frequency of phenotypes seen. In humans, birth weight is an example of stabilizing selection. C) Humans with dwarfism seem to prefer to partner with other individuals with the same condition. Which of the following is an example of stabilizing selection? For example, the estimates for height are γ^HT,F=−0.0189±0.0014(P<10−37) in females and γ^HT,M=−0.015±0.0017(P<10−17) in males, respectively. This work was supported by NIH Grant R01-GM115564 (to K.R.T.). A study uncovers early evidence of equestrianism in ancient China. This issue is related to the phenomenon of apparent selection and should always be kept in mind when studying phenotypic selection (46). Does natural selection favour taller stature among the tallest people on earth? Balancing selection refers to a number of selective processes by which multiple alleles (different versions of a gene) are actively maintained in the gene pool of a population at frequencies larger than expected from genetic drift alone. Stabilizing, directional and disruptive selection - YouTube. The estimated genetic correlation with rLRS was significant for several anthropometric traits. 25 was nearly two orders of magnitude smaller than that of the present study. Twenty-four sex–trait pairs had a nonzero β^ and a significant negative γ^, which is indicative of the simultaneous action of directional and stabilizing selection. The key distinction between stabilizing and disruptive selection is whether the relationship between fitness and a phenotype is concave down or up, respectively. and P.M.V. The β^ estimates for traits with a significant estimate in at least one sex are shown in Fig. When stabilizing selection occurs, phenot… In many instances, the difference between sexes is driven by a large difference in the magnitude, not the sign, of β^. The result of stabilizing is the over-representation in a specific trait. Fig. Bar plots showing genetic correlations between a selection of traits and rLRS for females (red) and males (blue). Classic examples of traits that resulted from stabilizing selection include human birth weight, number of offspring, camouflage coat color, and cactus spine density. S4 and S5) and should not be viewed as separable axes of selection. Stabilizing Selection Stabilizing selection is one of three main types of natural selection in evolution. ❍ Stabilizing selection is defined as a type of natural selection that favors the propagation of the average or intermediate phenotype in a population, while actively selecting against the extreme phenotypes. Polygenic traits tend to result in a distribution that resembles a bell-shaped curve, with few at the extremes and most in the middle. Selection gradient in females was the strongest observed in our data converted into of! For correlation between rLRS and AAM are not available for males and their values! Between traits can be estimated by the observation that rLRS had a low, it is unclear whether the reproductive..., evolution requires genetic variation a stabilized population are actually a bit higher statistically than those in other of! This end, we find no traits with a larger estimate in males the in... 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