While molecular evolutionists may be fascinated by the features and history of a particular gene or DNA segment, evolutionary anthropologists are often more interested in the activities and history of groups of people. We may want to know, for instance, when and where humans have migrated, how much exchange between groups has taken place, and how population sizes have changed. Population genetic theory provides the hope that through analyses of genetic data we will gain insight into the history of populations. Genetic data from extant human populations are now accruing at a remarkable rate. We might, therefore, expect to have answers in hand. There remains, however, a wide gap between the available theory and data; too often we fail to draw firm conclusions because our interpretation of analytic results requires that we make myriad assumptions about our data. In any one instance, these assumptions might include estimates of mutation rate, mutational mechanism, population sizes, the role that natural selection has played, and the rate of migration among groups. Often these assumptions are implicit, invisible to most. How, then, are we to make any progress?
Evolutionary Anthropology 21
Glossary
Admixture-formation of a new population through contributions from two or more other, divergent populations.
Allele-a particular genetic variant. An individual has two alleles, one inherited from each parent, at each autosomal locus. These two alleles may or may not differ from one another.
Autosome-any chromosome other than a sex chromosome. Humans have two copies of each of 22 different autosomes.
Base-in DNA, one of the four units, adenine (A), guanine (G), thymine (T), or cytosine (C), that combine with a sugar and phosphate backbone to form a nucleotide chain.
Classical markers-the first set of polymorphisms surveyed in human populations. Includes blood groups, protein and enzyme polymorphisms, and immunologically important loci.
Coalescence-the most recent common ancestor of two or more current alleles at a locus. When one considers the process of divergence in reverse, a divergence between alleles then becomes a coalescence. Consideration of this reverse process has lead to powerful theory for making inferences about the history of alleles at a locus. Coding region-any segment of the genome that codes for a protein. Only a fraction of the more than 3 billion base pair human genome thus codes.
Convergent evolution-the process whereby a similar allele evolves independently in two species or populations.
Crossing over-the process in which, during meiosis, a pair of chromosomes exchange genetic material.
Diploid-Having two sets of genes and two sets of chromosomes, one from each parent. Humans are diploid in that the nuclei of their cells contain two copies of each autosome.
Divergence-extent of genetic difference between two alleles, individuals, or populations.
Fitness-the average number of offspring produced by individuals having a particular genotype relative to the number produced by individuals with other genotypes.
Gametes-haploid reproductive cells that combine during fertilization to form the zygotes (sperm in males and eggs in females).
Gene-sequence of nucleotides coding for part or all of a protein.
Gene flow-the movement of alleles into a population or among populations through migration and interbreeding.
Gene geneaology-relationship among a set of alleles at a locus; also called a gene tree.
Genetic drift-random changes in allele frequencies in a population over time. The extent of such change in each generation depends on the size of the population.
Genetic linkage-the tendency for two alleles at two different loci to be inherited together. The primary reason for genetic linkage is physical linkage: If two loci are near each other on a chromosome, a father, for instance, will usually transmit to his offspring the two alleles he received from his mother or the two alleles he received from his father (Fig. ).
Genotype-the set of two alleles, one from each parent, that an individual inherits at a locus.
Haploid-having one set of genes and one set of chromosomes. The NRPY and mitochondrial DNA are essentially haploid genetic systems.
Haplotype-the alleles at more than one locus that an individual inherited from one parent. These alleles are found on the same chromosome.
Heterozygosity-proportion of individuals in a population that are heterozygous or the proportion expected to be heterozygous given the allele frequencies.
Linkage disequilibrium-the tendency of two alleles at each of two loci to be associated with each other on chromosomes (as for alleles a and b in Fig. ).
Locus-a locality within a genome; often refers to a gene, but