photo of tops of milk bottles

Are humans still evolving?

Are we still subject to natural selection?

The minuscule doors of medieval houses suggest that people were shorter then than they are now. We do seem to be getting taller – but that’s due to better diet rather than any evolutionary change.

With most people now surviving to reproductive age (at least in rich countries), have selective pressures been completely eliminated?

Direct evidence would be changes in the frequency of particular alleles over time. As evolution is usually a slow process, it is difficult to see it taking place directly. There is some evidence that selection for resistance to HIV is altering the make-up of populations in Africa. Selection is acting on the major histocompatibility complex, a large set of genes involved in defence against infections.

But we can also use indirect methods. One is to compare our genomes with those of our relatives, such as chimpanzees, and to find examples of genes under positive selection. Another approach is to map the geographic distribution of particular alleles. Sometimes alleles can be seen gradually spreading outwards from a source. For example, an allele that increases women’s fertility very slightly seems to be spreading southwards from northern Europe.

One of the most striking examples of recent human evolution is the emergence of lactose tolerance. Our ancestors could not digest lactose, the main sugar in milk, in adulthood because the gene encoding a lactose-digesting enzyme, lactase, is switched off in childhood. Genetic changes leading to lactase production in adulthood have occurred independently on several different occasions in different parts of the world, including Europe and Africa.

Lactase persistence alleles have spread widely because they provide a selective advantage in cultures generating milk through agriculture. Even so, lactose intolerance remains common in many parts of the world where milk is not so important in people’s diets. So despite our best efforts, it seems we are still subject to the forces of evolution.

Lead image:

Guy Montag/Flickr CC BY

References

Questions for discussion

  • Do you think humans are still evolving? How?

Further reading

About this resource

This resource was first published in ‘Evolution’ in January 2007 and reviewed and updated in December 2014.

Topics:
Genetics and genomics, Ecology and environment, History
Issue:
Evolution
Education levels:
16–19, Continuing professional development