natural selection in humans

For example, it is still unclear what percentage of the human genome has been shaped by natural selection, which genetic variants are responsible for the phenotypes that make humans unique, and to what extent demographic factors hav… I proceeded analogously for males. Whether or not humans are still subject to natural selection all depends on what we define as natural selection. Population-specific causal disease effect sizes in functionally important regions impacted by selection. It has also been shown that there was significant variance in relative fitness in a preindustrial human population, such that there was much potential for natural selection (15). Consistent with the results of my regressions of rLRS on phenotypic BMI and HGT (Table 1), there is previous phenotypic evidence of positive selection for weight and negative selection for HGT in females (9, 45). The polygenic scores of EA were accessed under Section 4 of the Data Sharing Agreement of the Social Science Genetic Association Consortium (SSGAC) and were constructed and provided by the SSGAC; I thank Aysu Okbay for constructing these scores on behalf of the SSGAC. For all phenotypes, I also regressed rLRS on the polygenic score of the phenotype in various samples; the regressions also included birth year dummies, HRS-defined cohort dummies, and the top 20 principal components of the genetic relatedness matrix [to control for population stratification (27); see also section 5 of the supplemental material of ref. The previously reported R2 for SCZ is the R2 on the liability scale. The phenotypes I analyze are BMI, educational attainment (EA), fasting glucose concentration (GLU), HGT, schizophrenia (SCZ), plasma concentrations of total cholesterol (TC), and age at menarche (AAM; in females). Better understanding the tradeoffs presented by different bioplastics should help elucidate which options, if any, are viable replacements over the long run. Shi H, Gazal S, Kanai M, Koch EM, Schoech AP, Siewert KM, Kim SS, Luo Y, Amariuta T, Huang H, Okada Y, Raychaudhuri S, Sunyaev SR, Price AL. Please enable it to take advantage of the complete set of features! doi: 10.7554/eLife.63177. S1 shows, LRS for females and males declined gradually between 1931 and 1953, from around three children in the early 1930s to two children around 1950. (My results are robust to using scores constructed with PLINK (34), which does not adjust the summary statistics for LD between SNPs.) Thus, although it is not possible to rule out with certainty that my results are (at least partly) confounded by stratification, stratification is unlikely to be an important concern. The author declares no conflict of interest. For the regressions in the sample of females and males together, I also controlled for sex and only included the respondent with the lowest PN in each household, as spouses very often have the same number of children, which induces a complex correlation structure between the error terms (the results for the score of EA are robust to alternative ways of selecting one respondent per household). The BMI phenotypic variable for males is defined analogously. The HRS contains phenotypic variables for BMI, EA, HGT, and TC. The HRS does not contain phenotypic variables for GLU, SCZ, and AAM (in females). This isn't on YouTube right now, and I hate HHMI's website, so I uploaded it. The molecular signature of selection underlying human adaptations. For each of BMI, EA, HGT, and TC—for which there are phenotypic variables in the HRS—I regressed rLRS on the corresponding phenotypic variable, separately for males and females; these regressions included birth year dummies and HRS-defined cohort dummies, and were estimated by OLS. I then examine associations between these scores and fitness to test whether natural selection has been occurring. The estimates for the sample of genotyped individuals are very similar (Table S2), thus suggesting that the two samples are similar in terms of the selection gradients that were operating on the various phenotypes. The HRS is a longitudinal panel study for which a representative sample of ∼20,000 Americans have been surveyed every 2 y since 1992. (As detailed in Materials and Methods, I define cohorts based on the individuals’ birth years; the study sample includes the HRS1, HRS2, and HRS3 cohorts, but excludes the HRS0 cohort because of possible selection bias based on mortality.) In most results tables, I report the coefficient estimates and SEs, with stars to indicate statistical significance; P values for the results shown in Tables 1 and 2 are reported in Table S2, and other P values are included in log files available upon request. Also, for the study sample, the estimates from the regressions of rLRS on the phenotypic variables are very similar between the sample of genotyped individuals and the sample of all individuals (Table 1 and Table S2). Hence, the estimates from Table 2 imply that natural selection has been operating on the score of EA at a rate of −0.033 Haldanes among females and of −0.031 Haldanes among males in the study sample. All of this implies that my main results are not driven by the weight selection procedure. My finding that natural selection has been slowly occurring for genetic variants associated with educational attainment and (suggestively, in females) for variants associated with age at menarche provides additional evidence that humans are still evolving—albeit slowly and at a rate that cannot account for more than a small fraction of the large changes that have occurred over the past few generations. Cactus– this plant developed needles to protect from animals 2. To avoid overfitting, I ensured that the GWAS summary statistics used to construct the polygenic scores for each phenotype are based on meta-analyses that exclude the HRS dataset (32). Which of the following terms could fill in the blank to make the statement true? Author contributions: J.P.B. (Selection on phenotypes that are genetically correlated with the phenotypes of interest impacts their genetic covariance, which, in turn, impacts the selection gradients on the phenotypes of interest in future generations.) The most significant estimate is that of the coefficient on the interaction of the scores of SCZ and TC in females (P = 0.007), but it is not significant after Bonferroni correction (it is not significant after Bonferroni correction for more than seven tests; coefficients on 28 squared or interacted scores are tested for females, and 21 are tested for males, so 49 tests are conducted in total). Kirk et al. I treat the polygenic scores themselves (as opposed to the phenotypes, as is usual) as the characters of interest and estimate the quadratic regression of rLRS on all of the scores and their squares and interactions together, along with birth year dummies, HRS-defined cohort dummies, and the top 20 principal components of the genetic relatedness matrix, separately for females and males in the study sample, by OLS. Future studies that address the above-mentioned limitations will be able to leverage these developments to replicate my results and to obtain more precise estimates of the rate at which natural selection has been and is occurring in humans. To ensure that the LRS variable is a good proxy for completed fertility, I only include females who were at least 45 y old when asked the number of children they ever gave birth to and males who were at least 50 y old when asked the number of children they ever fathered. Depending on the phenotype, there were between 505,254 and 544,493 such overlapping SNPs (except for GLU, for which there were only 22,895 such overlapping SNPs). The HRS is a representative longitudinal panel study of ∼20,000 Americans shortly before and during retirement. Several additional caveats should be kept in mind when interpreting my results. Table S4 presents the results of those checks. Gravity. Previous studies have also documented a positive (9) and an inverted-U (45) relationship between LRS and phenotypic HGT in males, and have found evidence of negative selection for TC and of stabilizing selection for GLU in females (11), in contemporary Western human populations. 2020 Dec 7;6(12):e05679. For the LDpred scores, the study sample individuals’ genotyped SNPs that passed the above quality control filters were used as the reference panel to calculate the LD between the SNPs. As I show in SI Materials and Methods, if we define the polygenic scores as the characters of interest, it follows that the coefficients on the scores reported in Table 2 can be interpreted as the directional selection differentials of the scores themselves, expressed in Haldanes—i.e., each coefficient equals the implied change in the score that will occur due to natural selection in one generation, expressed in SDs of the score per generation. That latter coefficient is significantly different from the coefficient in the sample of females who have not been genotyped (P = 0.009, t test of the interaction between the coefficient on EA and a dummy for genotyped individuals), suggesting that sample selection bias is at play for the HRS0 cohort. The scores were standardized to have mean zero and an SD of 1. Online ISSN 1091-6490. Examples of natural selection include: 1. Both the LDpred and the PLINK scores for an individual are weighted sums of the individual’s genotype across all SNPs. The individuals’ genotyped SNPs that passed the above quality control filters and that were present in the phenotype’s summary statistics files were used to construct the polygenic scores. The second equality follows because the nongenetic component of rLRS is independent of the genetic component of EA (by definition) and thus of PGS of EA, the third equality follows from the fact that the score of EA has been standardized to have unit variance, and the last equality holds if the other covariates in the regression of rLRS on PGS of EA are uncorrelated with PGS of EA (which is a reasonable approximation). This site needs JavaScript to work properly. Second, I used polygenic scores constructed with PLINK (34) instead of LDpred. Natural Selection in Humans SUGGESTED AUDIENCE This lesson is appropriate for high school biology (all levels including AP and IB) and undergraduate introductory biology. Previous research, however, has established that these phenotypes are all moderately to highly heritable (31); notwithstanding the possible effects of correlated phenotypes, this is suggestive that genotypes associated with BMI, EA, and HGT covary with fitness and that natural selection has been operating on these phenotypes. BMI was measured in each wave of the HRS, and the BMI phenotypic variable for females is the mean across waves of female BMI residualized on birth year dummies, plus the mean female BMI across all waves. Natural selection, a concept first theorized by Charles Darwin, is the adjustment of genes throughout generations based on factors that help living organisms survive. Zeng Z, Liu H, Xu H, Lu H, Yu Y, Xu X, Yu M, Zhang T, Tian X, Xi H, Guan L, Zhang J, O'Brien SJ; HBVstudy consortium. Table S8 shows the parameters used to construct the scores and the sources for each phenotype’s summary statistics. An infectious disease could act as a function of LRS, by.. 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