So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

When a population experiences a reduction of its effective size, it generally develops a heterozygosity excess at selectively neutral loci, i.e., the heterozygosity computed from a sample of genes is larger than the heterozygosity expected from the number of alleles found in the sample if the population were at mutation drift equilibrium. The heterozygosity excess persists only a certain number of generations until a new equilibrium is established. Two statistical tests for detecting a heterozygosity excess are described. They require measurements of the number of alleles and heterozygosity at each of several loci from a population sample. The first test determines if the proportion of loci with heterozygosity excess is significantly larger than expected at equilibrium. The second test establishes if the average of standardized differences between observed and expected heterozygosities is significantly different from zero. Type I and II errors have been evaluated by computer simulations, varying sample size, number of loci, bottleneck size, time elapsed since the beginning of the bottleneck and level of variability of loci. These analyses show that the most useful markers for bottleneck detection are those evolving under the infinite allele model (IAM) and they provide guidelines for selecting sample sizes of individuals and loci. The usefulness of these tests for conservation biology is discussed.

https://www.genetics.org/content/genetics/144/4/2001.full.pdf

Description and Power Analysis of Two Tests for Detecting Recent Population Bottlenecks from Allele Frequency Data

Just over one hundred and thirty years ago Charles Darwin, in The Descent of Man and Selection in Relation to Sex (1871), developed remarkably accurate conclusions about man's ancestry, based on a review of general comparative anatomy and psychology in which he regarded sexual selection as a necessary part of the evolutionary process. But the attention of biologists turned to the more general concept of natural selection, in which sexual selection plays a complex role that has been little understood. This volume significantly broadens the scope of modern evolutionary biology by looking at this important and long neglected concept of great importance. In this book, which is the first full discussion of sexual selection since 1871, leading biologists bring modern genetic theory and behavior observation to bear on the subject. The distinguished authors consider many aspects of sexual selection in many species, including man, within the context of contemporary evolutionary theory and research. The result is a remarkably original and well-rounded view of the whole concept that will be invaluable especially to students of evolution and human sexual behavior. The lucid authority of the contributors and the importance of the topic will interest all who share in man's perennial fascination with his own history. The book will be of central importance to a wide variety of professionals, including biologists, anthropologists, and geneticists. It will be an invaluable supplementary text for courses in vertebrate biology, theory of evolution, genetics, and physical anthropology. It is especially important with the emergence of alternative explanations of human development, under the rubric of creationism and doctrines of intelligent design.

/pdf/sexual-selection-and-the-descent-of-man-1871-1971-446kq7o7lj.pdf

Sexual selection and the descent of man, 1871-1971

ilbstract. Autocorrelation is a very general statistical property of ecological variables observed across geographic space; its most common forms are patches and gradients. Spatial autocorrelation. which comes either from the physical forcing of environmental variables or from community processes, presents a problem for statistical testing because autocorrelated data violate the assumption of independence of most standard statistical procedures. The paper discusses first how autocorrelation in ecological variables can be described and measured. with emphasis on mapping techniques. Then. proper statistical testing in the presence of autocorrelation is briefly discussed. Finally. ways are presented of explicitly introducing spatial structures into ecological models. Two approaches are proposed: in the raw-data approach, the spatial structure takes the form of a polynomial of the x and .v geographic coordinates of the sampling stations; in the matrix approach. the spatial structure is introduced in the form of a geographic distance matrix among locations. These two approaches are compared in the concluding section. A table provides a list of computer programs available for spatial analysis.

https://www.jstor.org/stable/pdfplus/1939924.pdf

Spatial Autocorrelation: Trouble or New Paradigm?

/pdf/evolution-at-two-levels-in-humans-and-chimpanzees-4j80qi0jr2.pdf

Evolution at two levels in humans and chimpanzees

Adaptive radiation has been defined as the evolutionary divergence of members of a phyletic line into different niches or adaptive zones (Mayr, 1963:633). Although it has been customary to think of adaptive radiation solely in terms of species or races, a growing body of evidence indicates that some degree of radiation occurs also within populations, as individuals come to occupy different subniches or adaptive subzones, subdividing and, perhaps, expanding the total niche or zone utilized by the population. Probably all species show some degree of ecological variation, either polymorphic or continuous. But this phenomenon is being studied in only a few groups of organisms, notably in Drosophila, in which chromosomal polymorphism has been interpreted as a. means of adaptation of populations to heterogeneous environments (Dobzhansky, * 1961, 1963, 1965). Theoretical bases for research on ecological variation in animal populations have been provided by Ludwig (1950), Levene (1953)) da Cunha and Dobzhansky (1954), Dempster (1955), Li (1955), Carson (1959), and Levins (1962, 1963). In birds, as in other vertebrates, the sexes usually differ in size if not also in proportions of body parts, including those used in feeding (Amadon, 1959) ; and, especially where the degree of sexual dimorphism, which is a form of polymorphism (Ford, 1961: 12), is marked, it seems probable that the morphological divergence has ecological significance in adapting the sexes to different subniches. However, there is only an occasional reference in the literature to sexual dimorphism in relation to niche utilization (e.g., Pitelka, 1950; Rand, 19.52), and, in general, the whole problem of ecological variation in populations has been neglected by vertebrate ecologists. The primary purpose of this report is to present evidence of an adaptive function of sexual dimorphism in size in woodpeckers by relating degrees of morphological dimorphism and sexual divergence in foraging behavior in two melanerpine species, the strongly dimorphic Hispaniolan Woodpecker (Centurus striatus) of Haiti and the Dominican Republic and the moderately dimorphic Golden-fronted Woodpecker (Ce&zmus awifrons) of continental North and Central America. In addition, the paper surveys other evidence that sexual dimorphism in birds is related to differential niche utilization. Finally, some evolutionary aspects of sexual dimorphism and ecological variation are considered.

/pdf/sexual-dimorphism-and-differential-niche-utilization-in-2q4rzlfv70.pdf

Sexual Dimorphism and Differential Niche Utilization in Birds

Blood samples from northern elephant seals (Mirounga angustirostris), representing five breeding colonies in California and Mexico, were surveyed electrophoretically for protein variation reflecting underlying genetic differences. No polymorphisms were found among 21 proteins encoded by 24 loci. This uniform homozygosity may be a consequence of fixation of alleles brought about by the decimation of this species by sealers in the last century.

https://science.sciencemag.org/content/sci/184/4139/908.full.pdf

Elephant Seals: Genetic Variation and Near Extinction

Attempts to understand evolutionary processes in cave organisms have been largely limited to speculation on the causes of loss of photoreceptor organs and pigmentation, increase in size and complexity of tactile sensory structures, and certain modifications in physiology (see review in Barr, 1968). Little is known of the population genetics of cave organisms or of the genetic changes accompanying the transformation of epigean (surface-dwelling) forms to troglobites (obligate cavernicoles). Yet genetic information is essential to the confident development of theories of troglobite evolution. For this reason, we have compared the genic character and degree of variability in troglobitic and epigean populations of the characid fish Astyanax mexicanus in Mexico. Students of cave biology have generally accepted the thesis that the ancestors of many troglobites entered caves as troglophiles (facultative cavernicoles) before the end of the Pleistocene, and became isolated with the local extinction of surface populations as a result of climatic changes associated with glaciation (Barr, 1968). If this is true, many troglobites have been living

Evolutionary genetics of cave-dwelling fishes of the genus astyanax.

Conspicuous adaptive differentiation in color and size has occurred in the house sparrow (Passer domesticus) in North America and the Hawaiian Islands since its introduction in the middle of the 19th century. Patterns of geographic variation in North America parallel those shown by native polytypic species, in conformity with Gloger's and Bergmann's ecogeographic rules. Racial differentiation of house sparrow populations may require no more than 50 years.

https://science.sciencemag.org/content/sci/144/3618/548.full.pdf

House Sparrows: Rapid Evolution of Races in North America

To many early evolutionists, particularly those of the mutationist school, the existence of evolutionarily stable forms ("living fossils" or phylogenetic "relics") posed a difficult problem, and, even among contemporary biologists, the feeling that "a long-standing stability of organization seems antithetical to the concept of evolution" may persist (Volpe, 1967:140). In the early part of this century, it was popularly believed that stable or slowly evolving (bradytelic) lines lacked the genetic variation necessary for more rapid evolution as a result of having abnormally low mutation rates; as Mayr (1963) puts it, a lack of variation in time and space was interpreted as a reflection of genotypic stability. Largely because of the influence of Simpson (1944), Stebbins (1944), Schmalhausen (1949), and Dobzhansky (1951), the mutationists' interpretation of bradytely has now been all but abandoned by evolutionists in favor of the view that the principal factors controlling rates of evolution are to be found in the organism-environment relationship. Additionally, Mayr (1963 :304) has suggested that phenotypic "uniformity in space and time is due to a highly perfected 'buffering system,' in other words, to genetic homeostasis." The ecological hypothesis is well expressed in Simpson's (1944:141) conclusions that "the final and probably the most fundamental factor in the relationship is that bradytelic groups are so well adapted to a particular, continuously available environment that almost any mutation occurring in them must be disadvantageous" and that "bradytely results from the equilibrium of large breeding populations of animals specifically adapted to a continuously available environment that is relatively invariable . . . ." Yet, as Mayr (1963) notes, there is no evidence to refute (or to support) the hypothesis that bradytely results from loss of mutability. The recent development of electrophoretic techniques for demonstrating allelic variation at loci controlling enzymes and other proteins in natural populations (Hubby and Lewontin, 1966; Lewontin and Hubby, 1966) permits a test of the mutationists' thesis. The purpose of this study is to compare degrees of protein polymorphism and underlying genic heterozygosity in a classic phylogenetic "relic," the horseshoe or king crab (Limulus polyphemus), and in several representatives of horotelic lines (those evolving at standard rates) for which data are already available. Evidence of a level of genetic variation in Limulus similar to that in horotelic forms will support the modern ecological and homeostatic interpretations of bradytely. But if the mutationists' thesis is valid, Limulus should show an unusually low degree of polymorphism at its genetic loci. Limulus polyphemus is one of five living species of the Subclass Xiphosura, a group of marine arthropods usually placed with the Subclass Eurypterida (extinct giant water scorpions) in the Class Merostomata of the Subphylum Chelicerata. Following a period of adaptive radiation in the early and middle Paleozoic, the Merostomata became much less prominent after the Permian. Several Mesozoic forms are known in the Family Mesolimulidae, but by the Tertiary the fossil record is all but absent. There are presently three living genera, all belonging to the Family Limulidae, only one of which, Tachypleus, is known from the fossil record (Stormer,

Robert K. Selander

Papers

Sexual Dimorphism and Differential Niche Utilization in Birds

Elephant Seals: Genetic Variation and Near Extinction

Evolutionary genetics of cave-dwelling fishes of the genus astyanax.

House Sparrows: Rapid Evolution of Races in North America

Genetic variation in the horseshoe crab (limulus polyphemus), a phylogenetic "relic".