And depending on how it might be applied, culture and technology could either isolate some people from others, or it could help to renormalize them to the rest. Meredith F. Small, associate professor in the anthropology department at Cornell University, offers one perspective:. We might think that because we have culture--and with it all kinds of medical interventions and technologies--that we are immune from natural selection, but nature proceeds as usual.
Evolution is defined as a change in gene frequencies over time, which means that over generations, there will be changes in the gene pool, and humans experience those changes as much as any other organism.
Some people live and some people die, and some people pass on more genes than others. Therefore, there is a change in the human gene pool over time. Take smallpox, for an example. Years ago millions of people died from smallpox, and their genes were not passed on because many of them died before reproductive age.
The human gene pool was then missing the genes of those people. But now, since smallpox has been wiped off the planet, people who normally died of the disease now live, probably have children, and thus contribute to the human gene pool. In another example, the birth rate always goes down the more developed, and economically affluent, countries become.
Today the highest birth rates are in Latin America, Africa and Asia. Such mutations are thus more likely to be passed on to the next generation, so they increase in frequency in a population.
Gradually, these mutations and their associated traits become more common among the whole group. By looking at global studies of our DNA, we can see evidence that natural selection has recently made changes and continues to do so. Though modern healthcare frees us from many causes of death, in countries without access to good healthcare, populations are continuing to evolve.
Survivors of infectious disease outbreaks drive natural selection by giving their genetic resistance to offspring. Our DNA shows evidence for recent selection for resistance of killer diseases like Lassa fever and malaria.
Selection in response to malaria is still ongoing in regions where the disease remains common. Humans are also adapting to their environment. Mutations allowing humans to live at high altitudes have become more common in populations in Tibet, Ethiopia, and the Andes.
The spread of genetic mutations in Tibet is possibly the fastest evolutionary change in humans, occurring over the past 3, years. This rapid surge in frequency of a mutated gene that increases blood oxygen content gives locals a survival advantage in higher altitudes, resulting in more surviving children. Diet is another source for adaptations. Evidence from Inuit DNA shows a recent adaptation that allows them to thrive on their fat-rich diet of Arctic mammals.
Studies also show that natural selection favouring a mutation allowing adults to produce lactase — the enzyme that breaks down milk sugars — is why some groups of people can digest milk after weaning. Over 80 per cent of northwest Europeans can, but in parts of East Asia, where milk is much less commonly drunk, an inability to digest lactose is the norm. Like high altitude adaptation, selection to digest milk has evolved more than once in humans and may be the strongest kind of recent selection.
Natural selection needs a 'selection pressure' e. Professor Stanley Ambrose, an anthropologist from the University of Illinois, explains that "any change in the proportions of genes or gene variants over time is also considered evolution. The variants may be functionally equivalent, so evolution does not automatically equate with 'improvement'".
Whilst some genes can be affected by natural selection e. Genetic drift works by chance: some individuals might be unlucky and die for reasons which have nothing to do with their genes. Their unique gene variations will not be passed on to the next generation, and so the population will change. As much as we have made things easier for ourselves, there are still selection pressures around us, which mean that natural selection is still happening.
Like all mammals, humans lose the ability to digest milk when they stop breastfeeding. This is because we stop making an enzyme called lactase. In some countries, the population has acquired 'lactase persistence', meaning that people make lactase throughout their lives. By studying this specific gene variation in modern and ancient DNA samples, researchers suggest that it became common after humans started domesticated and milking animals.
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