Humans are curious about their origins. Children ask, “Where did I come from?” Teens wonder whether they were switched at birth. Seniors dig into genealogy on websites that attract thousands of users. People of all ages read about extinct humans in the news and in best-selling books. Celebrities discuss their DNA ancestry tests on television and recommend websites where viewers can buy them, too.
Commercial ancestry tests and the research tests used by anthropologists and population geneticists employ similar techniques, comparing test and reference samples to look for patterns of genetic similarities and differences. For example, Ancestry Informative Markers (AIMs) are sets of genetic variants that are known to differ in frequency between specific human populations. Markers derived from mitochondrial DNA (mtDNA, passed from mother to child) and the Y-chromosome (passed from father to son) are used to trace lineages.
Population genetics is a statistical science, measuring and revising estimates of genetic variation with new data. An individual person’s DNA test results can answer meaningful questions only when they are compared with results from populations (e.g., “could I have ancestors from the Middle East?”) or other individuals (e.g., “could I be related to this person with the same last name?”). Personal ancestry test results that are inconsistent or lack meaningful context can leave users confused and disappointed. To help address these issues, the American Society of Human Genetics has called for the development of “scientifically based, ethically sound, and socially attentive guidelines” for ancestry testing.
As genotyping technology gets faster and cheaper, companies and researchers alike are able to test more people using larger sets of markers, such as genome-wide panels of single nucleotide polymorphisms (SNPs). The results enrich a growing knowledge base on human evolution, migration, and genetic variation in modern populations.
A new article in Nature Reviews Genetics summarizes the challenges and implications of research that last year produced the first three genome sequences from extinct hominins. Genome-wide data from these ancient individuals and from contemporary human populations support the theory that modern humans descend from a single group that migrated from Africa and later inter-bred with two groups of now-extinct relatives, the Neanderthals and Denisovans. All non-Africans carry traces of Neanderthal DNA.
Human migration patterns can be inferred from genetic admixture, which results from inter-breeding of genetically distinct populations. Observed patterns at the population level reflect the results of thousands of instances of sexual reproduction, which shuffles the genetic deck between generations. Recombination between inherited parental chromosomes during meiosis creates germ cells with a mixture of segments from each one. When sperm and egg combine, a new remix is born.
Recombination does not occur at random throughout the genome but is more likely at “hotspots.” New research published last week provides the most complete recombination maps yet developed for African-American populations. These maps will be useful not only to population geneticists but to epidemiologists searching for associations with health and disease.
In an eloquent multi-part video essay titled “Everything is a Remix,” New York-based filmmaker Kirby Ferguson draws on examples from music, film, and scientific discovery to argue that the essence of creativity is the remix: copy, transform, combine. The same process generates new variations on the human genome, creating individuals who are genetically unique, yet descended from the common ancestors of everyone alive today.