I recently read an article called, “Evolution stops here: Future Man will look the same”. It was written by a David Derbyshire and it quotes a geneticist named Steve Jones from the University College London. He posits that humans have stopped evolving because we no longer interface as intimately with our environment as we once did. Now we live in houses, have central air and plenty of food. The article also says that the decrease in older fathers, leads to fewer mutations passed on to offspring—because mutations in sperm cells accrue over an individual male’s lifetime. And with increased travel and globalization, there are fewer isolated populations of people, and this may cause a decline in the randomness that evolutionary change is predicated on.
It’s possible that some of the geneticist’s original points may have been lost in the brevity of the journalistic translation. So I address the following points to the article, not necessarily to the geneticist, and to you.
Firstly, it is true that our relationship to the environment has changed dramatically in modern times. We do live in houses with central air and we do have an abundance of agriculturally grown and processed food. However, we don’t all have the HVAC technician on speed dial and we don’t all have a stockpile of twinkies, ding-dongs or ho-hos. What about contemporary non-Western societies that subsist on hunted or gathered food stuffs? And what about the poor schleps with no central air, like me? I think this article underrepresents the heterogeneity with which modern humans, from all parts of the world, interact with their environment. It is true that some hunter-gatherer populations are dwindling in the face of increased agricultural practices, but they are not gone yet.
Alternatively, Western practices such as controlled housing temperature and our new processed diet may present some novel selective pressures of their own. For example, our increasingly sedentary lifestyle and our ubiquitous consumption of processed products such as high-fructose corn syrup. These elements of our society are the new selective pressures. Childhood obesity is skyrocketing, and I cannot imagine this will not have some effect on the fitness, meaning how many viable offspring are produced, of this new generation.
There may be fewer older fathers than there were in the 18th century, but what about older mothers? In this case, our culture is evolving and is selecting for mothers who are able to have successful offspring—who are themselves reproductively fit—into their later years. True, this seems like a predominantly Western phenomenon, but women are having children later and later in life. This can lead to increased stress on the mothers body and it increases the possibility of offspring having chromosomal abnormalities, such as down-syndrome. This can’t mean nothing for our species. This may have some long term effect on our life history, and more specifically, the increment of time that females are reproductively fit. Mothers who have healthy daughters later in life may pass on the trait of being able to have successful offspring later in life. Longevity and reproductive health are, to some extent, heritable. Or perhaps mothers who have daughters later in life may pass on inability or difficulty in having successful offspring. All female babies are born with all of their eggs, perhaps the development and viability of the female fetus’ eggs is affected by the mothers health and age during gestation.
And what about artificial insemination, IVF or assisted hatching? Do we know the long term fitness effects that these novel reproductive practices may have on our species? No, I don’t believe we really do. And I say this with a gentle hand, quite simply, offspring are being born who would otherwise not be. Genes are being passed on to the next generation that would otherwise not be. What is their fitness level, how many successful offspring will they have, and what traits will they then pass on to their own offspring? So, while prezygotic selective pressure may be abated through these new medical practices, I cannot imagine that the subsequent population will not differ in its genetic and physiological landscape.
Evolution is random. Mutation and genetic drift both shape the population’s collective genome in a random manner. This author suggests that the lack of isolated human populations will halt randomness. It is true that genetic drift—or the selection of alleles from one generation to the next based on stochastic sampling—is stronger in smaller populations. But genetic drift is not absent in larger populations. Also—while it may be more rare and less random than we once thought—mutations do continually arise and lead to novel phenotypes that interact with the ever changing environment.
And what about the environment, or large scale climate change? For one thing, global warming can affect the ecological habitat of some parasites, like Plasmodium which causes malaria, and that can affect humans. Microorganisms that lead to diseases that we don’t have inexpensive widespread cures for, are key in the evolution of our species. Individuals who are resistant or less susceptible to disease, because of a random mutation, survive in the population to reproduce, others don’t. The flu virus rapidly mutates every year, so as long as viruses and bacteria are still evolving, we will be too.
The point is, adaptations to temperature, diet, reproductive robusticity or disease resistance, may still be relevant to the evolution our species. Natural selection may no longer be traditionally “natural”, but it’s still selective. And maybe more directly, “Woman Still Uncertain about Future Man” is not as sexy a headline as “Evolution stops here: Future Man will look the same”. And perhaps Future Man will fuel vehicles with Hostess snowballs and wear t-shirts that say “Only Losers Evolve”, but then again, we wont really know.