As a species, humans have populated almost every corner of the earth. We have developed technologies and cultures which shape the world we live in.
The idea of ‘natural selection’ or ‘survival of the fittest’ seems to make sense in Stone Age times when we were fighting over scraps of meat, but does it still apply now?
We asked 12 experts whether humans are still evolving. The expert consensus is unanimously ‘yes’, however scientists say we might have the wrong idea of what evolution actually is.
Evolution is not the same as natural selection
Evolution is often used interchangeable with the phrases ‘survival of the fittest’ or ‘natural selection’. Actually, these are not quite the same thing.
‘Evolution’ simply means the gradual change of a population over time.
‘Natural selection’ is a mechanism by which evolution can occur. Our Stone Age ancestors who were faster runners avoided being trampled by mammoths and were more likely to have children. That is ‘natural selection’.
Overtime, the human population became faster at running. That’s evolution.
Evolution can happen without natural selection
That makes sense for Stone Age humans, but what about nowadays? We don’t need to outrun mammoths, we have medicines for when we’re sick and we can go to the shops to get food.
Natural selection needs a ‘selection pressure’ (e.g. dangerous trampling mammoths), so if we don’t have these anymore, does this mean we stop evolving?
Even with no selection pressures, experts say evolution still occurs by other mechanisms.
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.g. genes that help us run faster), other changes in our DNA might have no obvious effect on us. ‘Neutral’ variations can also spread through a population by a different mechanism called ‘genetic drift’.
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.
Genetic drift doesn’t need any selection pressures, and it is still happening today.
Natural selection is still happening in humans
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.
In European countries we can thank one specific gene variation for our lactase persistence, which is called ‘-13910*T’. 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.
This is an example of…
Read More News: Are Humans Still Evolving? Scientists Weigh In
