Has human evolution stopped?

Cecil's Columns/Staff Reports
1

Link to column.

I’ve often wondered if humans could be bred as we breed dogs, given enough time of course and the requisite absolute dictatorship. In time could we have as many varieties of humans with as many different shapes as dogs? I read an sf novel once (The Dragon Masters by Jack Vance) in which men bred captive aliens and the aliens bred captive humans resulting in a fearsome array of altered men and aliens who were used as weapons of war against their own kind.

I thought the story pure fantasy at the time. Now I’m not so sure. If dogs and other creatures can be forcibly evolved why not humans?

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Well … if we assume evolution selects for “accumulation of resources” … then people over seven foot tall are being very strongly selected … check out salaries in professional basketball …

3

Dogs have an unusually plastic phenotype and also have been domesticated for something like 30,000 years. Compare this to the cat, perhaps 4000 years, and unusually resistant to phenotype manipulation. All we’ve managed to do with the cat is change its fur and its head shapes. That’s about it.

It’s possible to change animals fairly quickly by inbreeding mutations which could never survive on their own. In order to do that you need to cull all offspring which do not conform to parameters from the breeding pool. For humans, that would require zoo-like living conditions.

Our breeding experiences with animals so far – dogs excepted – would lead me to tentatively conclude that it is fairly easy to breed animals for changes in body type, such a increased or decreased size, deformed bones (dwarfism, brachycephalism), and simple mutations such as, in sheep, the genes which cause wool to be retained instead of shed seasonally. Also pigmentation.

Other than that, it is surprisingly difficult to produce ‘improvement’ in domestic species. That’s why it is a popular hobby (breeding animals for ‘show’) and an ongoing challenge for the farming industry. Breeding for only one quality tends to negatively affect other qualities.

Breeding humans for distortion’s sake would be possible, if absolutely immoral. Breeding humans for super-human powers doesn’t seem probable at all.

4

What you’re describing with dogs is usually called artificial selection - deliberately breeding for chosen characteristics. This can obviously proceed much more rapidly that natural selection. In the wild, a trait might give a fitness advantage (loosely, expected number of offspring) of a few percent. But artificial breeder looking for a trait obviously impose a selective pressure of 100%.

Now, strong selective pressure tends to reduce genetic diversity in the population - obviously so, because only a small proportion of the population are passing on their genes to the next generation. In the wild, where selection is much slower, over hundreds or thousands of generations, natural DNA mutations will tend to regenerate the genetic diversity. But artificial selection is much too fast for this to occur.

So, for example: if you try to breed dogs for large size, initially you can proceed very rapidly, but you soon reach a limit, because you have used up the standing variation - the preexisting genetic diversity in the population. If every dog is now genetically identical, no amount of selective pressure will do anything.

So, to do fantastic stuff with humans will require something that looks very different from either natural evolution or artificial selection in dogs. It can’t be done just by selective breeding, it must be done by active genetic manipulation. So the question is not so much “what can evolution do”, it is “what can biotechnology and bioengineering do”.

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If evolution is defined as “adaptation to environment through a process of natural selection”, then, yes. Humans no longer adapt to their environment. They adapt the environment to them.

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I’ve mentioned before, we already do this, the best and brightest and most beautiful always mate first and more often. And I always use the example of the Kardashians. They are phenomenally successful, and yes, I know, they are to an extent gaming the system – redefining what is best, brightest, and most successful. But that’s the point, the natural selection of advantageous traits isn’t interested in your definition of evolution/devolution, it was always all about just barely getting ahead any way you can.

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I’d say the flaw in your assessment is that having more children is not the first thing every “phenomenally successful” human tries to do, if anything I think the stats show that more successful people tend to defer having families, and don’t have larger families; while on the flipside we have social welfare systems that means the kids of the “phenomenally unsuccessful” still survive.

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A future filled with Kardashians? Stop the planet, I want to get off!

9

Incorrect.

The problem is that people don’t fully consider what the term “environment” encompasses. It’s not just hot/cold, sun/shade, and so forth. It’s also toxins, diet, disease, and so forth.

As just one example: the ability to continue to digest lactose into adulthood is a relatively recent mutation that became widespread after certain human groups domesticated cattle and started using their milk for food.

Another one: the sickle cell trait, which became common because having one gene for this gives you improved resistance to malaria, and it continues to be perpetruated due to malaria still being a serious and widespread disease.

Another one that is a double-whammy: “thrifty genes” that enable more efficient food storage for people in environments subjected to food shortages but that also make diabetes more likely when food is more plentiful and steady in supply. On the flip side, other groups that lose these genes when they acquire and abundant and steady food supply that makes for less efficient food storage (perhaps the energy is used elsewhere, for growth or reproduction or something) but also reduced chance of diabetes in such an environment. People with hunter-gatherers as their immediate ancestors tend to have “thrifty genes”, people whose ancestors have had agriculture for long periods tend to have the other version. These are both in response to the local environment.

I have no doubt that we are currently undergoing selection for resistance to various new chemicals and toxins that were previously either extremely rare or entirely non-existent in our environment thanks to the chemical wonders of the past century and a half.

Immunity/resistance to some diseases is known to have a genetic component, and humans have been impacted by the Black Death, smallpox, measles, malaria (already mentioned), and there are gene-based variations in resistance to HIV as well (from delayed illness to complete immunity). Some of these will become more or less common as such diseases spread, retreat, or are entirely eliminated.

That’s just the natural selection we are still undergoing.

Assuming some sort of controlling entity (aliens, human despot, whatever) using just current human diversity we could probably be breed for a considerable range of heights (probably around 4 feet up to 7 or so), variations of pigmentation from extremely pale to very dark, different textures and straight/curly hair variations, different eye colors, musculature ranging from lean/endurance to stout/burst strength (a mutation already exists that gives a person significant more muscle than the average), ear/ear/nose shape, and probably a bunch more.

We might also be bred for longevity - there is already some evidence that families that go generations of reproducing later than average not only tend to retain their fertility to a later age, but also tend to live longer with the reverse - those that go generations reproducing early tending to die slightly earlier - also having some evidence. If either a natural cause, societal pressure, or alien overlord intensifies selection to favor the late-breeding folks then humans will, after many generations, tend to reproduce later and life and live longer… but since that trait also seems coupled with slightly lower overall fertility that would be incompatible with a situation with high mortality among the young (which tended to be the case for a lot of human history).

Likewise, ANY trait that has a genetic component can be increased or decreased by selective pressure, either natural or artificial. That could be intelligence, dexterity, language ability, all sorts of things… many of which we probably were selected for in the past, hence our intelligence, dexterity, language ability… The only hitch is that in biological systems trade-offs are the norm. A trait beneficial in one environment (genes that promote iron intake, making anemia less likely) can be detrimental in another (iron overload when a person eats an iron-rich diet can damage major organs and kill the person relatively young).

That’s just the tip of the iceberg. We still have pressures on us as a species, they’re just not as obvious as a tiger leaping out of the bushes to eat us.

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It’s the difference between r and K selection.

While humans overall are K strategists (lots of investment in few offspring) within the range of human possibility there are still people who are more K than others.

There is STILL a higher death and disability rate among the poor, who tend to reproduce earlier and more often. By human standards they’re “r strategists”. They have more children, put fewer resources into each one, but hope at least one of them will “pay off”.

But, keep in mind that in most human societies the poor have at least some chance of getting on top, from the Roman emperor that was the grandson of slaves to the American meme of the self-made man. There’s enough churning between the lower and upper ranks of societies that no, we are not going to wind up a species of poor/morons/criminals/degenerates/whatever.

Besides which - if the poor are able to produce more children, which then produce more children, by living on the “dole”, requiring less effort on their part, then regardless of how you personally feel they actually ARE more successful in a Darwinian sense than the super-wealthy who reproduce less. They have found a niche and are exploiting it. They are no more wrong or evil or less moral for finding a way to exploit their environment than are the wealthy who find a way to extract more resources from society than the average person.

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Human evolution hasn’t stopped and will never stop, but I suspect it has seriously slowed down. We can modify our environment more than it modifies us.

To give an example, picture what cavemen were like, over a hundred thousand years ago, before the invention of clothes (whenever that occurred). Such people could not have lived in the subarctic. However people have lived in the subarctic for tens of thousands of years - after the invention of (warm) clothing and footwear, shelters, and weapons to take down the animals whose resources can be used to create said warm clothing. (In many areas, this was paired with evolution; lactose intolerance would be a problem up north if you didn’t want to get rickets. Less sunlight meant you got less vitamin D, and milk is a good source of vitamin D. Less important today, since you could order vitamin D pills on the internet. Or hunt animals that you know have a lot of vitamin D.)

Our environment changes, but we change ourselves faster. If climate change caused food production to increase on one continent and decrease on another continent, new commercial and shipping arrangements will crop up faster than genetic changes that impact our metabolism.

From what I’ve read, welfare recipients have on average the same number of children as other people, so it’s hard to say they’re more successful from a reproductive perspective. However, they’re not less successful.

As for breeding humans like dogs, that’s an interesting question. I don’t think we would see such drastic changes, but possibly we would see better results than domestic hamsters, which have very little genetic variability (supposedly all from four hamsters found in one burrow). There’s still a lot of variation in color and even size among domestic hamsters. (For that matter, there’s a lot of variation in color and size among humans. And hair. And dentition. And eye color.)

12

To some extent, but there’s more to it than that. It’s quite clear that Bill Gates has ample resources (and ample sperm) to support several thousand children. And how do you account for wealthy people who choose to have no children at all? Humans now have far more power and resources than we had in the ancestral environment, so the tools that evolution used to manipulate our behavior toward fecundity are no longer so effective.

And, although you make some good points, I don’t agree with your blanket dismissal of the notion that evolution (really we’re talking specifically about natural selection) has stopped. I think in part it’s a question of semantics. Natural selection is to some degree a tautology - that which copies itself more becomes, well, more numerous - so of course it will always occur. But the fundamental insight of natural selection is not that it occurs, but that it explains apparent design. What may certainly be true is that human ability to modify ourselves and our environment has become so powerful that evolution by natural selection is no longer a significant factor in biological design change.

13

Yes, this.

I think the answer that humans are still evolving is technically right in a pedantic sense but misleading in most contexts (given the reasons why people ask this question and what they generally think evolution means).
Human evolution has slowed to a crawl thanks to increases in healthcare, food production and general quality of life for all. Meanwhile human society and technology is changing at breakneck speeds and will only accelerate going forwards.

That’s why I think it’s usually clearer to say something like: Technically we’re still evolving, but we’re changing our environment so quickly as to make it an irrelevance.

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Took issue with one statement, that humans may be evolving resistance to HIV. Highly unlikely in one generation. Maybe if it had infected and killed a large portion of the human population. Its more likely the virus has evolved into a less virulent form. The strains of HIV that keep people alive longer to spread the virus would become more common than those strains that make people sick and dead in a short time. Over a much shorter period of time, a “kinder” virus would be the dominant strain.

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A Troublesome Inheritance by Nicholas Wade is a recent book on this subject. The book repeatedly uses the phrase “human evolution is recent, copious and regional”.

The book discusses recent genetic findings in relation to cultural differences among human societies.

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I didn’t say one generation - it would take many.

Also, the genetic resistance to HIV is already in place in some individuals. One variation may have survived in Europe due to granting greater resistance to the plague, and it just happens to also work to give resistance to HIV as well.

And yes, the virus may be evolving into a less virulent form, there’s no reason both phenomena can’t be happening at once.

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I’m firmly on the side of continuing human evolution. The mechanism for evolutionary change is mutations, and this is still happening. Every once in a great while, and individual human will have a beneficial mutation. I don’t know of anything that is stopping this. It does take far more time for this beneficial mutation to spread through the gene pool, however time is one thing we have in abundance. The 200,000 years that Homo sapiens (or H. s. sapiens if you wish) have been here is but a snap of the fingers in evolutionary terms.

Humans have also seemed to already evolved to exploit the wide variety of ecological niches. They’re like a plague upon the face of the Earth and exist in rather large numbers on all the landmasses. Humans even have a continuous habitation in space. I would put forth the conjecture that this is inhibiting the Homo genus from further speciation. The current human DNA allows exploiting tropical rain forest and sub-arctic tundra equally well. There doesn’t seem to be any selection pressure on what could be argued as the single most adaptive species in existence. Although we can find many genera of world-wide distribution, it is quite rare to find a single species thus and of course no other species has come to so thoroughly dominate every square foot of land like humans have done.

This has brought the Homo genus to the brink. Typically, a genus will have some radiation and more diversity so that if any single species should die off completely, the genus itself will continue. If anything (and evidence is extremely slight), the Homo genus is contracting. It’s down to not only a single species, but one with an amazingly homogeneous gene pool. All it takes is one mutation in one pathogen and … poof … Homo sp. is added to the dust bin of evolutionary failures …

18

But this is exactly what I’m talking about. Ignoring human technology, industry and communication to draw dubious “we’re nothing special” conclusions.

Yes 200,000 years is a snap of the fingers in evolutionary terms, but you know what’s many orders of magnitude shorter than that? A human generation. And within that kind of timespan the world has changed in myriad ways, with just a single example being a revolution in our understanding and ability to sequence and manipulate organisms’ genomes.

In terms of pathogens, just this year we had an stunningly fast journey from detection to vaccine for the new strain of zika. And a flu vaccine that may protect against multiple strains. And this is with little money / urgency in the field relative to other pharma.

How can we assume that these and subsequent technologies won’t radically change the playing field by the year 2100, or 2500? Let alone 400,000.

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Gregory Cochran and Henry Harpending also make the case that human evolution has sped up in their book The 10,000 Year Explosion: How Civilization Accelerated Human Evolution, though I haven’t read it.

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Mijin has just written something like what I was about to post, so to go further - the key is the exponential growth of technology. Unless we have some kind of apocalyptic civilization-disrupting event that takes us back to the Middle Ages, within 1000 years we’re going to have AIs that are orders of magnitude smarter than us that probably take technology into a hyper-exponential phase, and if we haven’t uploaded our minds to in silico consciousness and abandoned biology altogether, at the very least we will be physically transformed, some combination of bioengineering and integrated synthetic elements… who the hell knows, but I think the chance that we still make babies through sex and straightforward inheritance of randomly recombined parental DNA without massive levels of manipulation and bioengineering is zero. The glacially slow mechanisms of natural selection that got us to the technological tipping point will be completely irrelevant.