What the human genetics of the past can teach us about the future

In 50 or 100 years, I think more people will have ancestry from different parts of the world. But this is only a few human generations, so I do not expect the genetic patterns that developed over thousands of years to disappear.

Also, people moving does not necessarily mean that they will have children together. Language, culture, religion and social circumstances still influence this, and will probably continue to do so.

Our research shows that people have always moved and mixed. Ancient DNA has made this particularly clear, revealing substantial population movements that we did not know about before. So I would be cautious about calling the present situation entirely unprecedented.

What has changed is how quickly people can move and how far they can travel. How this affects our genetic makeup will depend on what happens socially and politically as well.

Embryo selection and editing are different

For reproductive technologies, I see clear benefits in helping families avoid passing on serious inherited diseases. But IVF, embryo selection and germline editing are quite different things. With embryo selection, you choose among the genetic combinations that the parents can produce. With editing, you change the DNA, and these changes could then be passed on to future generations.

I am much more cautious about selecting or editing complex traits. Most traits and many diseases are influenced by many genetic variants, together with the environment. We cannot read a genome and reliably predict what a child will be like.

Also, the same variant can have several effects. Something that is beneficial in one respect might be harmful in another, or under different conditions. We still have a lot to learn about this.

Where do we draw the line?

I think we should be very cautious about allowing germline editing for reproduction because of the ethical slippery slope. We might start by allowing edits to prevent a few serious diseases, but commercial interests could push for more and more allowable edits. Where do we draw the line, and who decides what is desirable?

In the end, this could lead to “designer babies” and a separation between those who can afford genome editing and those who cannot, as in the film Gattaca. I do not think this is inevitable, but it is something we need to think about before going down this route.

There could also be pressure on parents to make these choices, and the future generations affected would have no say in the decision.

Genomic research needs broader representation

Another concern, from my work in Africa, is that we still know much less about some populations than others. Africa has more human genetic diversity than any other continent, but much of this diversity is still poorly represented in genomic research.

Predictions developed using one population cannot simply be assumed to work equally well in another. We need broader representation, with researchers and communities involved in the work and sharing in its benefits.

Our genes do not determine everything

What I would most like people to understand is that our genes influence us, but they do not determine everything about us. A genome can tell us about ancestry and some aspects of health and disease risk. It cannot tell us everything about who we are or what our future will be.

It is also important to understand that humans do not fall into distinct biological races. We can see genetic patterns related to geography and population history, but these come from a long history of shared ancestry, separation and mixing.

Why genetic diversity matters

And I would really like people to realise that genetic diversity is a good thing, as any plant or animal breeder will tell you. Genetic variation allows populations to adapt when conditions change.

Although there are billions of us today, humans have relatively little genetic diversity compared with many other large bodied mammals, including several of our closest primate relatives. Our ancestors lived in much smaller populations and went through bottlenecks where genetic diversity was lost.

Our historical “effective population size” – the population size reflected in how genetic variation is passed between generations – is therefore much smaller than our census size numbers today might suggest. Becoming billions does not immediately bring back the diversity that was lost.

Having less genetic diversity can make it harder for a population to adapt to new challenges, including infectious diseases. If people differ genetically in how susceptible they are to an infection, it is less likely to affect everyone in the same way.

Today, many people live close together and travel widely, making it easier for pathogens to spread quickly around the world.

We compensate to some extent for our low genetic diversity through technology and medicine, for example through vaccines, treatments and sanitation. But these do not remove the value of genetic diversity, which gives populations more possibilities to adapt when conditions change.

So we should treasure the little genetic diversity we have rather than fear it. Countries should celebrate the diversity in their populations rather than try to oppose or suppress it, or use it as a reason to exclude people. Our history is full of movement and mixing, and this is part of what has made us who we are today.