Are humans beyond evolution? No!

| 15 Comments

A common riff on the role of medical and technological advances is that they have somehow insulated humanity from evolution, or the ordinary course of evolution. This is an old canard - it goes back to the days before Darwin, and is a basic justification of eugenics programs (not just the Nazi horrors, but the more “positive” programs of encouraging the “better” kind of humans to interbreed).

It is thought that if medicine has interfered with the selective pressures we faced in the past, we will face degeneration, or be in control of our own evolution, or something, that will interfere with the “normal” course of evolution.

A [url = http://www.prospect-magazine.co.uk/[…]rticle=12713]very nice article[/url] by Gabrielle Walker in Prospect Magazine, a UK publication of The Independent, discusses this in some detail.

You’d think that after we encountered AIDS, MRSA (methicillin resistant Staphylococcus aureus), bird flu, swine flu, West Nile virus, and the host of new and altered diseases that occur to us annually, we would not be so sure. But there is more.

It is often overlooked, in part because we think of what we humans do as being not a part of Nature, but of Art (the division is as old as Greek philosophy - Art is techne in Greek), that our own cultural activities both construct a niche to which we will eventually become adapted, if it persisted long enough, and also provide new selective pressures.

For a start, there has been extensive selection against diseases that only get a purchase in urban environments in Europe. Alleles that confer resistance to bubonic plague are widespread - I wonder why? Is there any reason to think that if a disease hit us today, our allele frequencies would not change so that resistant alleles became widespread, to the point where the disease was unable to spread further, vaccines and antibiotics notwithstanding?

Moreover, there is selection against (for example) lactose-intolerance that has been applied in a very brief period, in evolutionary terms. All through Asia now, this selection pressure is being applied. You don’t need to die for selection to apply, just do slightly worse at raising children and grandchildren and greatgrandchildren, etc., than those who do not have the gene you do.

Even if we can manage to modify genes directly, this does not stop evolution. One of two things can be true, or both. The genes we use will have been “tested” elsewhere before we use them, in other humans or other organisms, in which case this is still just a spread of gene alleles through selection - the fact that scientists rather than gametes spread the genes is largely irrelevant, as what happens after those genes are introduced will be independent of the scientists anyway - they are, evolutionarily speaking, a blip on the radar.

The other is that introducing these genes individually into a complex developmental program will have massive unlooked-for effects - the Pandora Principle. Biology is replete with things that are massively interlinked - if you, for example, reactivated the fossil gene for the production of Vitamin C, it may turn out that in certain environments this caused liver failure. These things are not easily predictable, if at all. And no matter how much is predictable, some outcomes will always not be.

So have we stopped evolving? We have not! Evolution is affected by behavior, this is the principle of the Baldwin Effect. It is time to lay this mistake to rest once and for all.

Late note: A new article in Nature reviews the evolutionary relationship between humans and bugs. The press release says

Emerging infectious diseases, which have shaped the course of humanity and caused incalculable suffering and death, will continue to confront society in unpredictable ways as long as humans and microbes co-exist, write authors from the National Institute of Allergy and Infectious Diseases (NIAID) of the National Institutes of Health in a review article published in the July 8 issue of the journal Nature.

The article itself discusses the evolution of pathogens and what we can do about it.

15 Comments

Fertility selection is still very active.

How do you mean?

Well, no matter how well technology has allowed us to resist viability selection, selection on how well we can reproduce is still very active. Most people when that say that “we have stopped evolving” only think of viability selection and not fertility selection. Although modern science has techniques to address infertility, they really don’t even the playing field.

Yes indeed. And even if we attend to viability because of one set of pressures (say, if we could prevent deaths from all diseases) there would still be viability pressures of other kinds (violence, car deaths, drug deaths, etc.). Messy buggers, humans…

Look Maw! No pinky toes.

You neglected to mention the effect of chance. For instance, you and I have managed to breed (not together, of course, but with other individuals) and our genes are already represented in the next generation of humanity. Reed Cartwright has not, at least not yet, and therefore we may see a decline in the Reed-Cartwrightness of humanity, and an increase in the Wilkinsishness or Myersitude. Even in an accident-free, perfect-medicine world, we’d still see random variation in the gene pool.

I also have to object to part of the article. There’s an assumption that evolution and selection are synonymous, for example,

The reason is that without natural selection to weed out problematic mutations, humans won’t just stop evolving - we will also start accumulating defective genes.

If we did somehow magically stop selection (and as you say, we haven’t), that doesn’t mean we’d stop evolving—we’d be evolving faster, as novel alleles would not be pruned out of the population and would just accumulate.

50.000 year-old human skull look pretty much like modern ones, but I don’t think we’ve got much evidence as to how much genetic change has occurred over the same period. Is there any real evidence that cultural evolution has somehow ends biological evolution? Indeed, why would anybody think it has? Arguably the emergence of culture creates a huge selection pressure for increased brain power since it multiplies the value of intelligence. Living in cities in a cosmopolitan world and exposed to a planet-full of disease germs may also increase the selection pressure for an improved immune system.

On second thought, I object to big chunks of the article. For instance,

On balance, then, it seems that Jones is right that in the relatively narrow confines of western societies, humans are no longer evolving.

is total nonsense.

The article is useful because it covers the range of opinion - it’s reportage rather than advocacy (and yes, it is very annoying yet again to find that someone 74 years after Fisher opened his book with “Natural Selection is not Evolution” still thinks the two ideas are identical). I expect it from Steve Jones. I don’t from Alexei Kondrashov…

On the relaxation of selection (if that is, indeed, possible for all aspects of humans), in such a case we simply have a random elimination of alleles when carrying capacity is reached. But if carrying capacity is reached and there are differences in the distributions of resources, then selection will apply. In the interim, though, we might find a faster evolutionary rate, depending on where and for whom. Sudanese children are subjected to a rather different distribution of resources than Minnesotans…

Lets not forget that a significant portion of people on Earth don’t live in western opulence with ample food, clean water and medicine. There will still be selective pressure on people living in third world conditions for things like disease resistance. Claims of immunity to the HIV virus in Africa spring to mind.

Claims of immunity to the HIV virus in Africa spring to mind.

The human genome is littered with retroviral inserts. It’s likely that these derive from ancient retroviral plagues where incorporation of the viral genome into the germline of the survivors’ lineages rendered them resistant to “infection from without”. I wonder if - assuming we humans have any surviving descendants a million years hence - our descendants will have incorporated the HIV genome.

Humans certainly are still evolving, it’s just hard to see, because we have been looking at it for too brief a period. At the same time, we can look at history and such data as we do have, and figure some trends:

  • Not all populations are “evolving” in the same direction! As noted above, there are very different pressures on different continents and smaller segments.
  • It’s a rough world these days, with a variety of *heavy* selection pressures. Whole races and subraces are being wiped out, or nearly so. For example: In just 500 years, the various aboriginals native to North and South America have been smashed into a few remnant populations, and a reddish streak in various mixed-race underclasses. In fact, aboriginals in general are doing poorly. Africa as a whole is experiencing a major die-off, not entirely due to AIDS. Older diseases and climactic changes are also involved here. Asia is teetering at the edge of a similar die-off. On the other hand, the survivors should be a hardier bunch, with widespread immunity to AIDS and perhaps some other diseases. The industrial nations are getting hit with milder but broad problems related to pollution, pesticide misuse, and a developing stream of drug-resistant diseases, aggravated by poor leadership in the USA.
  • At the same time, some things don’t change. The species has gained noticably in height even since, say, Roman times. Since height is still considered desirable, there seems no reason to expect this to stop. Large breasts are likewise popular, so they will likely continue to gain “share” throughout the species. Health, fertility, and social status will remain the major draws.
  • The growing UV flux from the ozone layer will probably favor darker-skinned types, individuals with better cancer resistance, and possibly innovative traits. Global warming will likewise favor heat-adaptive sorts. (thinner build, etc.)
  • Socially-adaptive evolution will likewise continue. There are still large populations with little ability to recognize other tribes as “human”. These will continue to get clobbered by groups that can organize larger forces and projects, because they’re more willing to work with outsiders. (The story of civilization continues.…)
  • In industrialized areas, there will be (continuing) selection pressure for various technology-related traits; the cognitive abilities underlying literacy and numeracy, manual dexterity, etc. There will *also* be ongoing selection for resistance to various sorts of pollution, from heavy metals to artificial estrogens. As implied above, infectious-disease resistance will also be “coming back into fashion”.
  • The advent of somatic-cell genetic therapy will act like other medical treatments, weakening the selection pressure exerted by treatable conditions. However, when germ-line therapy comes along, that will overwhelm those medical effects, for any treatable gene. (GLT lets us actually remove the offending genes themselves, rather than the individuals bearing them!)

I’m sure others can find other points…

Methinks we are pretending to discuss a forest, but our noses are pressed against the bark of a single tree. We are bounded in a nutshell and count ourselves kings of infinite space.

Gould observed in his book The Massive Doorstop of Evolution that certain lineages tend to speciate at a high rate; others almost never. Primates fall in the “almost never” group. Furthermore, speciation is at least plausibly speculated to occur among isolated small populations on the periphery of the territory of the species, but humans are found in more of the planet’s territory than anything else (perhaps in a tie with roaches and rats we bring along?) We are not isolated geographically or genetically; humans have interbred lustily throughout all known history, and accelerating mobility has only boosted the rate. The conditions for a branching event are as poorly met by humans as can be imagined.

Maybe I’m unable to grasp the sheer pace of scientific progress, but I doubt we’ll generate any new human species (or defy the stasis of equilibrium our circumstances require) through genetic engineering and horizontal gene transfers either. We’re a LONG way from engineering “superman saltations” or whatever.

The evidence on the ground argues against the kind of genetic directional change David Harmon describes. Paleontologists “watched” with fascination the life forms abundant on the warm, damp, sea-level territory as (over 15 million years) that territory moved North, rose thousands of feet, and dried to the desert of what is now Wyoming. And did these life forms migrate genetically to the changing adaptive peaks? No, they did not. Those which could tolerate the change did so; those that could not went extinct. Neither group underwent gradual adaptive change. Granted, there were still speciation events and the newly branched species were better suited to the changing environment. But the pioneers never varied. Whatever it is that enforces the Eek part of PunkEek is immensely influential. There is no reason humans should be any exception, even if the above conditions (found planetwide and interbreed everywhere) didn’t apply.

As a Proper Darwinian, I predict that IF small colonies of humans populate habitable planets elsewhere in our local spiral arm or wherever, THEN we will see evolution with a vengeance. But PunkEek is a Goldilocks-type observation. The branching group can’t be too large (or the statis factor will rule), nor too small (and succumb to inbreeding) nor interact too freely with the main population. Conditions must be Just Right. Colonizing Mars, and then the colony losing contact with Earth for 10,000 generations, should do the trick. IF our models are accurate.

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GWW:

Hello again. I agree with you with what I hope are the usual caveats: That some humans survive, that they do so in small isolated populations, that the environments these populations inhabit are hostile but not fatally so, and that these populations remain isolated for enough generations for selection to have significant influence on them.

Frankly, this future holds little appeal for me; I think I’d prefer to be at ground zero…

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This page contains a single entry by John S. Wilkins published on July 12, 2004 7:17 PM.

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