Debunking myths on genetics and DNA

Saturday, November 8, 2014

Are we really evolving into super-humans?


I came across an article on the Popular Science website, which, turns out, is the excerpt of a new book on evolution by Science Guy Bill Nye. From the reviews I gather that Bill Nye is an excellent writer and, being also an entertainer, he knows how to not only expose well but also infuse some good humor to what he says. That's all fantastic. But while the article starts off with some rigor, his conclusion had me roll my eyes. Because, even though he does include some speculations that he himself labels the "science fiction future of human evolution" (which of course I agree is always fun to do), by the end of the article he's doing science fiction without calling it science fiction. So I'd like to take the chance to discuss what I did not like of the excerpt from his book.

Nye starts off asks the following question:
Is there a Homo superius just around the next corner, waiting to take our place?
This is the part of the excerpt that I contest:
We cannot step away from evolution. Our genomes are always collecting mutations, and we are always making mate selections. Are humans preferentially mating with other humans who are tall? Blonde or not blonde? Are smart people actually producing significantly smarter offspring, who end up making more money and ever so slowly outcompeting other families? [. . .] I'm looking out for big changes that come from good old-fashioned Darwinian natural selection. What trait would give a future human baby such an edge that she or he will grow up to produce some amazing new kid that can do something that stands out and will attract a similarly worthy partner with whom to mate? 
I understand Nye wants to make an impact on people who love science and in particular those who don't have a technical background to understand the nuisances of a scientific theory but still appreciate the importance of scientific rigor. The purpose of his book is to make people think, "This is cool. I totally get evolution." At the same time, I do believe that anyone attempting to popularize such a debated topic should go the extra length to make sure everything he/she says is rigorous, because if it isn't, it becomes easy target for those people who, instead, want to contradict it.

My points in particular are:

1) In his book he gives examples to illustrate evolution in action that are beautiful and clear and make valid points on how evolution works. But those changes have taken tens, sometimes hundred thousands of years to take place. Yes, you can draw the same examples from viruses and bacteria, but again those organisms evolve on a much faster clock than we do. So, you can't just blatantly extrapolate those examples and speculate, based on those, what will happen in the next few decades or centuries to the human species. There aren't "big changes that come from good old-fashioned Darwinian natural selection" on the time scale he's looking at. Nothing really changes on a scale of 100 years -- that's roughly only 4 generations. On the other hand, there are other things that are changing scarily fast and will hugely impact our lives in the next 100 years: climate, for example. Food and water are likely to get scarcer. And given how fast those are changing compared to how evolution works, the sad reality is that there is no adaptation that can save us this time. If the climate were changing on a scale of tens of thousands of years we could predict a new adaptation to the rising temperatures. But on this scale? Our only hope is technology and our own good will to fix things we've badly broken.

2) Intelligence. First of all, intelligence doesn't make us any more resistant to any pathogens and in particular not to the antibiotic resistant ones. The last Ebola strain that jumped from bats to humans did not ask the target person his or her IQ before infecting them. Intelligence might prompt you to vaccinate yourself and your kids, but so long as the vast majority of the people still believe in vaccines we have herd immunity protecting even the non-vaccinated people. On the other hand, there are many social constraints that put a cap on how "intelligent" the human species can be. Social events are valued more than isolated hours of working/studying/researching, and if you look back at the lives of people who've made a difference in science, literature or medicine (just to name a few), you'll see a common pattern: they were pretty unsociable. They chose their one passion over spending time with family and friends. Those are isolated cases because again, as a species, we have social constraints that only a few outliers escape.

3) "We are always making mate selections," says Bill Nye.
No, we aren't. Single individuals make mating choices under geographical and socio-economic constraints. We, as a species, make no choice. Even though cultural and socio-economic constraints are pretty stable, interbreeding has always happened and it's not going to stop now that geographical mobility has greatly increased compared to 200 years ago. When you look at the individual level you see choices. When you zoom out and look at the species level it's all random. And of course mutations appear randomly, but those who do reach fixation through this process they do so because of random drift, not because of mating choices, especially in today's globalized world.

Rather than mating choices, we need to look at geography, as Coop et al. have done in a paper in PLoS Genetics:
It seems likely that selection in humans is generally not divergent enough to generate large frequency differences at individual loci between population pairs that are either recently separated, or regularly exchange migrants. Furthermore, populations may be too mobile, or their identities too fluid, to experience very localized pressures consistently over the several thousand years that may be required for large allele frequency changes [3].
Does that mean that selection is no longer happening?

Selection and adaptation are of course still happening, but under very particular conditions. Nye does mention a few in his article: the Spanish Flu and the Black Death. Those events inferred a selective sweep on the human genome. But you can't just mention those and forget what happens in between those selective sweeps because that actually covers the majority of our evolutionary history. Most of the mutations found in our DNA have reached fixation through random drift, yet you never hear people say that. So many evolution "experts" out there go on and on on how every single gene in our DNA has been selected and perfected through evolution. This argument, not only is simply not true, but it makes evolution an easy target for the creationists because they (rightfully) say it's wrong. Random mutations, just because they are random, can be either favorable or not depending on the environmental conditions.

The mutation that causes a disease called sickle cell anemia is an interesting example: people are affected only when they carry the mutation on both gene copies. Heterozygous people, who carry the mutation only on one gene copy, are healthy. Since the disease significantly reduces the life span of affected people, under normal conditions, you would expect a deleterious mutation like that to gradually disappear from the population. So why is it still quite prevalent, especially in sub-Saharan Africa?

A study (you can read the whole post here) compared two African populations and saw that the population where the mutation was more prevalent had a lower incidence of malaria. It's only a hypothesis, but this could possibly mean that, under particular circumstances (i.e. endemic malaria), the mutation actually confers an advantage on healthy people who carry it on one gene only -- a phenomenon called heterozygote advantage. Now, this is selection in action. However, notice that the study was conducted on isolated African populations. In fact, the smaller the population, the faster selection acts. Unfortunately, in today's world there are only few pockets left of isolated human populations.

Another study I discussed a few months ago was able to find the effect of selective sweeps caused by historically documented epidemics in the genomes of the Rroma people. This population was ideal for this kind of analysis because over the centuries they remained ethnically homogeneous and only rarely intermingled outside of their group. In fact, one can retrace the migration of ancient populations looking at the people's genome, a concept pioneered by the great population geneticist Luigi Luca Cavalli Sforza.

We can definitely retrace the past, but the question is: can we really predict the future?

What would really help the debate is to hear the voices of real scientists, but real scientists get all technical and frankly what Bill Nye is saying when he envisions a super-intelligent human walking on Mars is far more appealing to the collective imagination than the concept of a handful of random mutations accumulating in our DNA. And as a science fiction writer, I get that because I do love to push the imagination. But then let's not call it science, let's call it what it really is: science fiction.

I'm writing all this not to criticize Bill Nye who's a science enthusiast working on spreading the beauty of science. And I do reckon that he has to do put a bit of this stuff in his book or else no publishing house would accept it. But they wouldn't accept it because us, the scientists, are once again failing to communicate not just the real science but the enthusiasm for (and the value of) scientific thinking.


[1] Salih NA, Hussain AA, Almugtaba IA, Elzein AM, Elhassan IM, Khalil EA, Ishag HB, Mohammed HS, Kwiatkowski D, & Ibrahim ME (2010). Loss of balancing selection in the betaS globin locus. BMC medical genetics, 11 PMID: 20128890

[2] Hafid Laayounia,1, Marije Oostingb,c,1, Pierre Luisia, Mihai Ioanab,d, Santos Alonsoe, Isis Ricaño-Poncef, Gosia Trynkaf,2, Alexandra Zhernakovaf, Theo S. Plantingab, Shih-Chin Chengb, Jos W. M. van der Meerb, Radu Poppg, Ajit Soodh, B. K. Thelmai, Cisca (2014). Convergent evolution in European and Rroma populations reveals pressure exerted by plague on Toll-like receptors PNAS DOI: 10.1073/pnas.1317723111

[3] Coop G, Pickrell JK, Novembre J, Kudaravalli S, Li J, Absher D, Myers RM, Cavalli-Sforza LL, Feldman MW, & Pritchard JK (2009). The role of geography in human adaptation. PLoS genetics, 5 (6) PMID: 19503611


  1. Great article. Very well reasoned and documented.

    The challenge when it comes to evolution is its glacial pace in regards to animals that live for decades. With artificial selection, we've been able to induce significant changes to the genome of dogs, cows, sheep, etc, but even those have taken thousands of years to get to where we have them today. Natural selection is far more laissez faire with genetic drift, sexual selection & naturally selective advantages taking hundreds of thousands to millions of years to accumulate.

    1. Thanks! More than "laissez faire", natural selection has no intention or meaning, whereas we do. :-)


Comments are moderated. Comments with spam links will be deleted and never published. So, if your intention is to leave a comment just to post a bogus link, please spare your time and mine. To all others: thank you for leaving a comment, I will respond as soon as possible.