Human evolution "at the crossroads"

8 minute read

MSNBC has posted a new entry in its series on "future evolution," this one covering possible scenarios for the evolution of our species in the future. This article is a concoction of wide-eyed speculation and slightly cautionary unconnected facts.

The basic story of the article is the fairly predictable idea that humans are going to look more similar to each other in the future:

At least for modern-day humans, the forces that lead to species spin-offs have been largely held in abeyance: Populations are increasingly in contact with each other, leading to greater gene-mixing. Humans are no longer threatened by predators their own size, and medicine cancels out inherited infirmities ranging from hemophilia to nearsightedness.


All of this is conventional wisdom, but I wonder how much of it is actually true. The effect of medical technology certainly does tend to cancel the selective impact of certain medical conditions, but that can hardly be said to reduce human genetic variability--instead it probably increases it. Likewise, the threat of predation has little to do with population differentiation, unless some of us have had to run a lot faster to escape from predators than others (aside: my voice recognition software inserted "creditors" instead of "predators," which of course demolishes my point).

The main fact supporting their idea of greater genetic uniformity in the future is the idea that populations are mixing with each other. By any measure, there are many times more people moving between large human populations today then would be necessary to make them much more uniform in the future than they are now. The rate of migration between populations necessary to support the current level of genetic difference is only one or two individuals per generation. Today we see many millions of people moving among large populations in every generation. Given this large scale human movement, many populations likely will become much more similar to each other.

But I wouldn't be so sure that this hasn't been the case in the past also. One or two people moving between populations every generation is not very many. If there many times that many people moving between populations today, it seems likely that the and there were all so many times as many moving between populations in the past. Some of the current genetic differentiation of populations is likely due to local selection in different places. That local selection may have changed in today's populations--it may even have disappeared. But we really don't know whether some of these factors remain, or whether new ones have arisen.

The prediction that human populations will become more similar depends on the assumption that selection has become everywhere uniform. But there could be very powerful selection on human populations right now that nevertheless has such slight effects in any one generation that we can't measure it. A selective advantage of less than one percent increased fitness in every generation can completely transform a population within a few thousand years. Yet such a small advantage would require the observation of reproduction in thousands of individuals to measure accurately.

The point is a simple one: we can't know what's going to happen in the feature because we can't measure what's happening now. Not only does our uncertainty depend on unexpected events that we can't predict, it also depends upon unobserved phenomena that are happening right now.

Can we say that humans won't speciate in the future? I think we can say this only to the extent that we believe that we haven't speciated in the past. If human nature really tends to extend our reproductive horizons across the boundaries of populations, as I think it does, then it certainly would seem unlikely that these horizons would be greatly reduced in the future.

On the results of a human speciation, the article says this:

Even in the event of a post-human split-off, evolutionary theory dictates that one species would eventually subjugate, assimilate or eliminate their competitors for the top job in the global ecosystem. Just ask the Neanderthals.

Of course there is no reason to believe that the competitive exclusion principle need operate in a cultural system like that in which humans are embedded. There is no conceptual barrier to accepting different species of humans coexisting. Nor is there necessarily a practical barrier. Although I'm not a member of this camp, there are many anthropologists to believe that humans coexisted until very recently with different species occupying different environments or even the same environments at the same times.

Even so, culture is a powerful force determining human behavior, so that the imposition of extreme cultural isolation upon a group, coupled with our likely future technological capacities, might lead to the rise of reproductive isolation. Consider an extreme religious sect with strong rules against intermarriage with other groups and access to the techniques of genetic engineering. How easy would be for this group to enforce its policy of isolation by including genomic elements in its members that would make reproduction with other humans impossible? Today this is an unknown answer, but it is unlikely to remain unknown for long. It could be that such a "speciation" would be reversible, if the genomic elements preventing reproduction could be removed. Or it could be permanent, with additional engineered elements serving as a sort of religious library of encoded information in the genomes of the sect's members. Who will be the first human to have the full text of a religious document inserted by genetic engineering into his or her genome? That person may have already been born.

Capturing our genetic legacy

Much of the article is concerned with the possibility that humans will increasingly incorporate robotic parts, becoming cyber-humans. This has little to do with human evolution per se, but it does include this interesting quote:

"When you talk to people in the know, they think cybernetics will become biology," [University of Washington paleontologist Peter Ward] said. "So you're right back to biology, and the easiest way to make changes is by manipulating genomes."


Really this gets down to the basic issue of whether and how humans will control their evolutionary future. If we continue to allow the independent assortment of genes as a random process, there will always be a random component to our offspring. But if people can pick which specific alleles they want to be expressed in their offspring, and can have those choices error-corrected to make sure that mutations don't occur during the reproductive process, then randomness is potentially gone. Certainly people want their offspring to be like them in general, but does this mean that you want your offspring to have all of your qualities? Today, those of us with biological offspring accept the fact that each of them will get half our genes--hopefully the better half, but possibly the worse half. Yet even today this is far from universal. Many people with giving hearts adopted raise children biologically unrelated to them. Others manage their infertility with the use of donor eggs or sperm. Parenting is not a statistical relationship, nor should it be. If the question is, "How many genes out of 20,000 must you share with your offspring in order to love them as a parent should?" then the answer is already zero.

On this issue we can safely say that our population is already prepared for the concept of introducing unrelated alleles into the conception of individual children. Assorting the alleles are already in a parent to choose one or more qualities of the offspring is barely genetic manipulation. What's really happening is the preservation of the genetic material chosen by the parent into the next generation. The intent need not be solely functional. A parent might choose to transmit a single noncoding genetic region to all of his or her offspring, like a bar code indicating the family crest. We could call it "assisted genealogy."

From the standpoint of introducing a permanent genetic changes in the populations, this kind of procedure--stacking the deck of statistical change--certainly is evolution. Indeed, it is merely an extreme case of meiotic drive. But in this case, the drive would often be in favor of healthy alleles against disease-associated alleles. If it were possible, humans would be exerting powerful purifying selection against some of their own alleles. The effect would be to increase the representation of some of their other alleles in future generations, ultimately by reducing the genetic variation in human populations related to reproduction.

At the same time, choosing the alleles of your offspring has the potential of making the diversity of human genomes as great as the diversity of human cultures. For some, this would have the positive effect of reinforcing cultural heritage. For others, it would be merely another venue to exercise bad taste. Lest you think that people will always choose what is best for their children, consider some of the extraordinarily bad names that people choose for them. One of the advantages of not messing with nature is that nature regularly outperforms human judgment. Will we in the future see the birth of children with highly exaggerated features of one kind or another? Will we see professional athletes selling snippets of their genetic code to parents hoping for the next Joe Montana or Babe Ruth?

From a legal standpoint, this last question raises an interesting issue. Presently under U.S. law, individuals have no rights over their own genetic code. In particular, companies and other individuals may use your genetic code or material for any purpose, even to the extent of obtaining patents for the exclusive use of your genetic code. But if the genome becomes a record that parents can use to codify information within their offspring, by deliberately incorporating certain genetic sequences, then the genome would be operating more like a book than a machine. In particular, the genome more and more appears to be software rather than hardware. As such, it may be subject to copyright. Can you assert copyright on year-end genome? An athlete or scientist wanting to sell parts of his or her genetic sequence to prospective parents certainly would hope so.

A prediction for the future: our genomes increasingly confirm the maxim that every person is a work of art.