Driving forces of human evolution
In human evolution the biological factors (hereditary variation, struggle for existence, natural selection, genetic drift, isolation) worked as in other species, as Darwin showed. They led to walking on two legs, the freeing of the hand, a larger brain and changes in the larynx and jaw. Social factors – making tools, living in groups, speech and thinking – are typical of humans: they develop quickly by cultural means (through learning) and can act much faster than changes in genes. Cooked food helped reduce the chewing apparatus; hunting and gathering needed cooperation; speech allowed experience to be passed to later generations. Selection now acts largely within culture: for example, the allele allowing adults to digest milk sugar (lactose) is common among herding peoples. All present-day people are one species, Homo sapiens; their DNA is about 99.9 per cent identical, and most of the variation (about 85 per cent) is found within a single population group. Marriages between people of different nations give healthy children. Outward traits such as skin colour and hair shape are noticeable but involve a very small part of the genome. Skin colour is an adaptation linked to sunlight: near the equator much melanin protects DNA from ultraviolet radiation, while in the north less melanin helps the synthesis of vitamin D. The traditional (older) classification divides people into the large Europoid, Mongoloid and Negroid races; modern genetics shows there are no sharply bounded biological groups among humans and that traits vary continuously. The race concept is historical, and there is no scientific basis for calling any people “higher” or “lower”; all peoples have the same biological potential and deserve respect and equal rights.
“We are one species”: a three-sided class discussion – outward traits, DNA and culture; each group gives three pieces of evidence for “Why are all peoples one species?”