Summary
Highlights
Evolution is defined as a change in the allelic frequency of a population over generations, explaining biodiversity. It's divided into microevolution (changes within a species) and macroevolution (speciation). Examples include dog breeds, selective plant breeding, and Darwin's finches. These mechanisms are crucial for understanding Biological Anthropology.
Mutation is the first mechanism, providing the raw material for evolution. Novel genetic changes allow natural selection to act. Beneficial mutations increase fitness and reproductive success, becoming common, while detrimental ones are weeded out. Mutations can cause small or large changes.
The ARHGAP11B gene, a human-specific duplication of ARHGAP11A, played a significant role in enlarging the neocortex. A specific C-to-G base substitution in ARHGAP11B led to a 47 amino acid sequence that triggers extra brain stem cells, demonstrating how mutations can have a profound impact. This gene's effect on brain size and folding has been observed in marmoset experiments.
Modern humans also exhibit beneficial mutations. Examples include the LRP5V171 mutation, increasing bone density, and the -13910*T mutation enabling lactase persistence in adulthood for many Europeans. The HbC variant of the hemoglobin gene provides significant protection against malaria, especially prevalent in Burkina Faso.
Genetic drift significantly impacted Neanderthals, leading to lower genetic diversity compared to archaic humans due to small population sizes. This resulted in the persistence of weakly detrimental alleles, akin to common inbreeding.
Gene flow, the exchange of alleles between populations, is evident in human evolution. Ancient DNA sequencing reveals extensive interbreeding between early humans, Neanderthals, and Denisovans. Modern Europeans may have up to 5% Neanderthal DNA, and Southeast Asians up to 12% Denisovan DNA. Interbreeding may have occurred for millions of years between species that diverged from the last common ancestor of humans and chimpanzees.