Are humans still evolving?

February 17, 2006 5:39 PM

Are humans still evolving?

I'm trying to settle something, and I'm curious. I'm fairly certain that human beings are still evolving, especially from many articles I've read about increased brain sizes, and such--but I've been presented with the idea that humans are 'stagnant' and not evolving.

I find this highly doubtful. I don't see why we wouldn't be. But I realize that I am not an expert enough to disprove this (or prove this, as it were).

So, anyone with a clue, or an expert (willing to go into at least a little detail)--are humans evolving?

posted by Lockeownzj00 to science & nature (34 comments total)

Yes, humans are still evolving. It's just happening really, really s-l-o-w-l-y. Think about geologic time -- every rock you see around you is moving, too. It's just happening so slowly, you can't see it.

That being said, I read recently that Tay-Sachs disease may become be a thing of the past, because of increased genetic testing. People are not passing along this gene as they used to. Is that evolution? Probably. Just not the way we normally think of it.
posted by frogan at 5:53 PM on February 17, 2006

I don't claim to be an expert on this - I took an intermediate-level class on evolutionary biology from Stephen Jay Gould, that's my qualification to answer this.

I think that if you buy into punctuated equilibrium - the idea that most evolutionary change takes place during periods of intense selection pressure, when there is a lot of dieback - then there is an argument to make that the last few millenia have not been a particularly active period for selective pressure against humans.

The proof is in population graphs; this one shows nearly exponential growth since 1950, but in fact world population growth has looked exponential for far longer than that. (You'd need a different scale to be able to see it on that graph; I can't find offhand a better graph to illustrate my point).

When population is growing exponentially, there's not much selection pressure. Directed evolution does not occur during these 'equilibrium' periods.
posted by ikkyu2 at 5:58 PM on February 17, 2006

If by "evolution", you mean are we non-stagnant, changing - then, yes, we are still subject at least to genetic drift.

If by "evolution", you mean are we subject to strong enough selection pressure to drive us in a particular direction in any reasonable stretch of time, as opposed to having found a solid niche, like sharks or crocodiles - well, thats debatable.

If by "evolution", you mean are we slowly but surely moving to become something "beyond" human - well, thats a misunderstanding of evolution - that is, evolution has no direction. (Though you can still argue more complex species tend to emerge over longer periods as a purely Random Walk analysis)
posted by vacapinta at 5:59 PM on February 17, 2006

I don't have an answer to your question, as it is something I have wondered as well. I am minoring in Anthropology and still haven't studied any research about human evolution in the present day.

I did recently read an article from the BBC which said a group of scientists measured a bunch of skulls from victims of the Black Plague and found that our cranial vaults/foreheads have increased significantly. He also said something to the effect of "500 years ago, people had more prominent features". I think the issue here is whether or not we attribute the change to evolution, or simply to better nutrition and environments.

I suspect that we must still be undergoing some sort of localized evolutionary processes. We have probably moved away from environmental pressures influencing our evolution, but I wouldn't be surprised if other mechanisms are at work such as sexual selection and the like.

IANA Anthropologist, so this is sort of just idle speculation.
posted by Paul KC at 6:02 PM on February 17, 2006

Humans were still evolving as recently as 5000 years ago, according to this. I see little reason that things should be different now than 5000 years ago. I would imagine that good candidates for genes undergoing evolution are those involved in disease - for instance if HIV continues at high prevelence I think we'll seen an increased frequency in people bearing mutations that confer resistance to HIV, such as in CCR5.

This is an active area of research. As genomics improves I expect we'll learn a lot more about recent human evolution.
posted by pombe at 6:06 PM on February 17, 2006

You're right: there's no good reason why we wouldn't still be, but here's an example of something significant that happened (evolutionarily) recently if that helps your argument:

This post on Accidental Hedonist today mentions that a mutation is responsible for switching off lactose intolerance in Eurasians, and one estimate for when it happened is ~6000 years ago. The Wikipedia (yeah, I know...) concurs.
posted by Opposite George at 6:16 PM on February 17, 2006

Sure. Indeed the Y chromosome is (slowly) falling apart, leading to "dire" predictions of the eventual extinction of males. ;)
posted by orthogonality at 6:31 PM on February 17, 2006

No, we're just getting more intelligently designed.
posted by BitterOldPunk at 6:35 PM on February 17, 2006

The core principle of evolution (natural selection) is not "the best survive", it's "the worst don't".

We've moved the bar up a LOT for natural selection. People with traits that wouldn't have survived long enough to breed even 50 years ago, now have a decent chance of doing so. Rather than being wiped out, those traits remain in the pool.
posted by Caviar at 6:40 PM on February 17, 2006

Well, on one hand, we're almost certainly still evolving. Even if you buy punctuated equilibrium, and feel that we're currently in an equilibrium period, we're not in equilibrium everywhere. Malaria still kills over a million a year in Africa. There may be genetic drift in areas affected by malaria, but not in the genes that provide resistance to it; they're still being selected for.

Furthermore, civilization's fondness for wars has a tendency to kill off males more quickly than females; I certainly haven't seen research on this, but I'd expect that to provide pressure for more females to be born (and before anyone cites Dawkins' arguments for why the male/female ratio will always be equal, that's exactly what I'm talking about... selection will encourage the number of child-bearing males and females to be equal).

On the other hand, while natural selection is still occurring, it does seem likely that on the scale of the whole species, its currently having a negligible effect on gene frequencies, even compared to the normal speed of evolution. Because individuals don't die very much, it would seem that to the extent it does occur, its working on reproduction rates.
posted by gsteff at 6:50 PM on February 17, 2006

The truest answer you're going to get is that we certainly are "evolving", but that artificial selection pressures are driving the change far more than the natural ones.

To understand part of why this is, you need to truly grasp that for the most part natural selection pertains to the survivability of offspring. Because of this, there is little selective pressure post-reproductive age, which provides one example of how contemporary humans are atypical. Viability and fecundity are very different things now in humans because of our technology.

With all due respect to Ikkyu2, who certainly is far more knowledgable on a great many things than me, certainly including biology, Gould when he died was not a professional authority on evolutionary biology, he was a paleontologist whose evolutionary expertise was out-of-date. There are people who are legitimately professionals in the field of evolutionary biologist. Punctuated equilibrium is, at best, a minority viewpoint among evolutionists and, worse, Gould's ideas about group selection are widely disregarded. If you want to begin to understand the current framework in which evolutionary theory works, then you can begin with George C. Williams's seminal 1969 work, "Adaptation and Natural Selection". Gould quite specifically fought against the adaptationist point of view—the view which is today easily dominant and elucidated quite well in Williams's book.
posted by Ethereal Bligh at 7:04 PM on February 17, 2006

But wouldn't the decadence of the body only leave the mind to evolve? I mean, articles like the one Paul KC mentioned (Was it the Damned Interesting one?) tend to prove to me that our brains are getting larger.

Homo sapien --> homo sapien sapien --> homo super saiyan?
posted by Lockeownzj00 at 7:13 PM on February 17, 2006

No-one leaps to talk about sexual selection? :)

I imagine that the traits that are desirable in a mate are constantly changing. Eg I would think that the availablity of education and a midde class in a modern developed nation makes an asthmatic brainiac a much more desirable commodity than 1000 years ago in the peasantry.

Plump women used to be considered generally more physically desirable, thin women now have that place in most areas.

So the overall demographics of who is mating with who changes with the various fluctuations of society, and the result is changes in the relative proportions of traits in the populace. Which is evolution.

Or maybe nothing has changed because thin women became more desirable at exactly the same rate that asthmatic brainiacs did :-)
posted by -harlequin- at 7:13 PM on February 17, 2006

Gould taught us adaptionism, gradualism, Lamarckianism, and all the other relevant, duelling concepts, contextualizing them historically. Along with Dick Lewontin, he also taught us about phyletics and tradtional cladistics, and the revolution in genetically-influenced cladistics. He was prolific as hell, too, both in the peer-reviewed literature and his books for both educated lay readers and the trade.

It was a great class and left me delighted and amazed at the depth of Gould's knowledge and understanding of evolutionary biology. All due respect to Bligh, whose contributions to MeFi I've appreciated muchly, but shitcanning Gould as an out-of-date paleontologist doesn't fly. Controversial, I'd buy; no consensus on his most prominent theories, sure; irrelevant, not so much.
posted by ikkyu2 at 7:13 PM on February 17, 2006

In terms of physical changes, supposedly human facial architecture is becoming more gracile, quite rapidly.

There was an article in Science last year (8 July 2005) called, appropriately enough, "Are Humans Still Evolving?" It's behind the subscription wall now, but there's a summary and discussion here.
posted by Sonny Jim at 7:14 PM on February 17, 2006

My personal feeling is that without selection pressures we're not evolving. Yes, there is a lot of sexual selection going on, but pretty much everyone is reproducing.
posted by delmoi at 8:09 PM on February 17, 2006

Sexual selection has been arguably very strong in humans—some argue, I believe (though don't rely upon me), that it had long been the dominant selective pressure. Clearly it continues to be important, but I didn't want to confuse the issue. But what delmoi said, too.
posted by Ethereal Bligh at 8:19 PM on February 17, 2006

i just want to point out that the state of civilization many of us have lived in for thousands of years could in and of itself be a selection pressure ... people who are innately more obediant to others may have an advantage ... people who aren't as likely to go on a rampage over something may have an advantage ... and people who are better able to drive 75 mph without smashing themselves into a tree might have an advantage

civilization is a challenging and different environment than the ones that our distant ancestors were used to ... over 5,000 years, isn't it possible that this has caused some selection in us? ... not a lot, but some?
posted by pyramid termite at 8:37 PM on February 17, 2006

artificial selection pressures are driving the change far more than the natural ones.

I agree, though the analysis thereof are likely very, very complex. There is still selection taking place, but bear in mind that without a high mortality rate and with lengthening lifespans, the normal operations of evolution are quite interrupted. A poor Bangladeshi who lives to age 30 and has 6 children, starting at age 18, is more evolutionarily "successful" than a Bill Gates, who is worth more than 40% of the US combined, yet has only 2 biological children of his own.

You don't have to live long to breed, and you don't have to be happy or powerful to breed. And breeding is the measure of success in evolution. Are we evolving? Sure. Are the rich and educated and successful out-competing the poor and disenfranchised? Don't count on it. Talk to a demographer to see where demographics are going. And then you'll get a sense of what genepools are going to be more salient in the future.

I will say that all socialist/populist programs in society (much as I believe in them) fly in the face of evolutionary history. A species who bends over backward to make sure that its paraplegic members can live normal lives is unheard of. Most of evolution has operated in a dog-eat-dog environment. Even things like taking care of elders is a huge shift.

It's much more complex than "are we still evolving." The answer is "yes, but in completely different ways than before."
posted by scarabic at 9:10 PM on February 17, 2006

Scarabic, your big-breeders-big-winners perspective assumes that with mere reproduction comes power and resources. The brutally frank reality of the world is that having six babies in a situation without sufficient access to resources is actually a drain on survivability. I'm not denying that the number of kids may play a role in distinguishing two families with equal economic and social power, but American 2-child home versus Bangladeshi 6-child home is more reliant on economic and social factors. In the short run and in the long run, access to power and resources plays a larger role in "fitness" than you suggest.
posted by squirrel at 10:19 PM on February 17, 2006

Evolution by means of natural selection happens at any given time on any living species. Unless individuals of a species are immortal, they will die and something will thus cause them to die. If some individuals are less prone to die from that cause, their genes will be passed down at a greater rate than those genes of the individuals who died. As long as humans are being killed by things that might have a genetic component (cancer, heart trouble, diabetes, high blood pressure, susceptibility to a particular disease, lowered immune response, etc.) those who have some genetic predisposition against death by one of those means will outlive those who lack this predisposition. Until we have a cure for all these diseases we will continue to evolve. It's never going to end.
posted by pwb503 at 11:03 PM on February 17, 2006

My friend with no wisdom teeth insists its because he's more highly evolved. Doubtful, but i just thought i'd throw those two cents into the ring.
posted by Kololo at 12:17 AM on February 18, 2006

Mmmm... I see your point, squirrel. I kind of assumed that most folks would start with that point of view, and my comments were meant to qualify it, not negate it. I think that most demographers would be happy to show you that while certain populations are accumulating power and weath, others are gathering huge demographic momentum. Both matter, to some extent.

But in the end I come down in favor of demographic strength, not economic or social power. Way back to the beginning, evolutionary success is defined as producing the greatest number of viable offspring. My point is that the bar for "viable" is very low by human standards. Just live long enough to breed and make sure your offspring do too. Perhaps many folks and their offspring will live in an oppressed state, while othersw have access to technology, wealth, and power. But does all that privelege really bestow an advantage in producing more viable offspring? Developed nations tend to breed less, actually.

The ecosphere of our planet is dominated by mostly pretty poor populations. As China industrializes this will become clearer and clearer. Those who had 18 kids 50 years ago will have a massive advantage over those who has a single child 5 years ago when the ecosystem experiences a disaster (which it always does, eventually).
posted by scarabic at 12:24 AM on February 18, 2006

I really think that pwb503s basic assertion is wrong. Selection against death only happens when death negatively affects fecundity. Yes, there are some auxilliary routes by which there is an indirect selection against death without regard to reproduction, but those are mostly speculative and most likely of little importance relative to the conventional selection pressures we're discussing here.

The single most important thing that most people fail to understand about evolution was implicitly stated by scarabic earlier. Evolution is not a teleological process. It is not a refinement heading to perfection. It is not even a process directed toward "better" in any sense other than reproductive success. One way I like to explain this is that there's a big noise component in the metaphorical signal that is a selection pressure in evolution, a great many "better" successful mutations, as we would think of them, are below the noise threshold. A guy once insisted to me that there is a selection pressure against male nipples and, eventually, they'd disappear. This is very wrong-headed.

Indeed, a very, very interesting argument Williams makes in the beginning of his book concerns the debunking of a pernicious form of teleology in evolutionary theory. He points out that it (was) commonly thought that evolutionary "advancement" was a progression from simple to increasing complexity. But he asks: how are you defining complexity? From one perspective, the life cycle of a caterpillar is astonishingly complex. To seriously think about evolution, I believe that it's necessary to ruthlessly attack one's (natural) predisposition to a teleological description of natural processes and the the tendency to assume anthropocentric value judgments. In the popular imagination, "better" or "worse" used in the context of a narrowly defined reproductive success with regard to evolution has come to mean "better" or "worse" in some absolute, Platonic sense.

I think a good counter-argument to scarabic's point is to look at what we're discussing in evolutionarily-relevant time spans (which are possibly shorter than we have believed, I've noticed from some new studies I've heard about). In the long-term, selection may ultimately favor the rich and powerful in a world that simply cannot support the poor and weak. In the interim, before that barrier is hit, scarabic may be right.
posted by Ethereal Bligh at 12:59 AM on February 18, 2006

Great post, Ethereal. I agree. But what is the explanation for larger brains? Even if it's not 'better,' it would seem humans are becoming more intelligent. What of that?
posted by Lockeownzj00 at 9:43 AM on February 18, 2006

Most people misunderstand evolution (even people who believe in and promote it). Yes, humans are evolving. Humans -- like all animals -- will continue to evolve forever (or until they are extinct or engineered into some sort of machine that is incapable of change).

For the most simplistic sort of evolution, all you need is multiple generations (check) and mutation (check). Let's say that my wife and I have "identical" quadruplets. They won't really be exactly identical. Each will be a unique mutation.

We get our genes from our parents, but we don't get carbon copies of their genes. We get "damaged" (imperfect) copies. There are several reasons why the copies are inexact -- one of which is due to cosmic radiation.

Our genes get hit by random cosmic rays and mutate. So each of our "identical" kids are actually a little different from each other -- and also different from us. Most of these differences will be SO minute that we won't notice them. But as the quads start to have children (with their own mutations) and their children have children (and so on) the differences will compound and -- after a STAGGERINGLY LONG TIME -- you may see a very different kind of person (different from me or my wife) emerge.

As all these mutants get born, some will be (through random luck of the draw) better able to survive than others. Mutations do NOT generally work on the following grand scale, but imagine one of our quads was born with only one leg, one was born with two legs and one was born with four legs. The four-legged one might be able to outrun the two-legged one (and definitely the one-legged one), which might give it an advantage.

If they're all racing towards a hot chick (and the hot chick doesn't care about the number of legs someone has), the four-legged guy will get to her first, mate with her, and pass his four-legged genes to their offspring. The two-legged one will eventually get to her, and he'll have a CHANCE of mating with her, but not as great a chance as his four-legged brother. So he MIGHT pass on his genes. Alas, one-legged Sam will just fall over. He'll never get to the hot chick, so his particular mutation will die with him.

(On the other hand, if the enviroment happens to favor one-legged guys, the outcome will be very different!)

So each child gets RANDOM advantages/disadvantages which make him more/less attractive to mates and more/less able to survive long enough to produce offspring. This is how evolution works.

Some people (here and elsewhere) make a distinction between natural and artificial changes, but I'm not sure how meaningful this is. We're part of nature, so whatever we do is natural. In the end, the environment is changing (due to "natural" change or our "unnatural" tampering) and each of us is randomly (or biologically) engineered to fit into it for better or worse. Some of us are reproducing without being selected by a mate (i.e. cloning), but there still IS a selection mechanism (i.e. I have more money than you do, so I can afford to be cloned).

One way to visualize all this is via letters of the alphabet. Imagine a Mom and Dad that look like this:

Mom: hello
Dad: cakes

Each letter is one gene. A child of theirs might have DNA like this:

Kid: halls

Notice that each letter comes from a different parent:

Mom: h(e)ll(o)
Dad: (c)a(k)(e)s
Kid: halls

The child has inherited the letters that aren't in parenthesis.

Actually, the child would inherit ALL the letters from each parent, but some would be active (dominant) and some inactive (recessive)

Mom: hello
Dad: cakes
Kid: h(c)a(e)l(k)l(e)s(o)

In the kid's child's DNA, some of the inactive genes might be active (and, of course, the kid's child will get half of his genes from the kid's spouse).

If we add in mutation, the kid will get some letters (capitals here) from neither parent. There will be random change:

Mom: hello
Dad: cakes
Kid: halQs

Let's say the "environment" is a novel. If the child's DNA can be understood as part of a sentence in the novel, it will have a better chance of reproducing (being used in other novels):

"Yesterday I ate some halQs and then went to bed."

This kid is a goner. But another possible child of "hello" and "cakes" is "calls," and still another -- with mutation -- is "haNls." That isn't a word, but if I wrote...

"I want to hold your haNls in mine."

...it might just survive extinction. And, in a subsequent generation, mutation (or letters gained via a spouse) might lead to haNDs.

If you want to explore "letter evolution," check out this toy I made years ago.
posted by grumblebee at 11:29 AM on February 18, 2006

Are humans still evolving?

Don't think of evolution as a mystical process. Modern industrial warfare, including genocide, forced famine and atomic bombs killed millions and millions of people all in this century. That's evolution. Birth rates are falling rapidly in the developed world. That's evolution. unparalleled sex selective abortions are occurring in India and China. That's evolution. An era of unparalleled mass migration is mixing thousands of ancient populations. That's evolution.

In short, yes, gene frequencies are shifting every generation, and in different patterns all over the world - humans are constantly changing.

But getting down to the hard evidence, a very important recent genetics paper showed that there has been major, major human evolution in the last 50,000 years (a blink of the eye in evolutionary time). I'll quote the New Scientist report:

This analysis suggested that around 1800 genes, or roughly 7% of the total in the human genome, have changed under the influence of natural selection within the past 50,000 years. A second analysis using a second SNP database gave similar results. That is roughly the same proportion of genes that were altered in maize when humans domesticated it from its wild ancestors.

Moyzis speculates that we may have similarly “domesticated” ourselves with the emergence of modern civilization.

“One of the major things that has happened in the last 50,000 years is the development of culture,” he says. “By so radically and rapidly changing our environment through our culture, we've put new kinds of selection [pressures] on ourselves.”

Also for important selection even in the last decade or so, see my comment on what we've done with Tay-Sachs and Downs.

Also search the MeFi archives for 'evolution', there have been a number of posts on this topic in the last couple of years.
posted by dgaicun at 2:07 PM on February 18, 2006

That's evolution.

To clarify all those listed events were based on non-random patterns of birth and death for millions of people. It's inconceivable that they didn't leave genetic changes in their path. It's not really possible to "stop evolving" - even if environments were completely stable and the species was completely panmictic (one population), nonfunctional mutations would build up differentiating the population identity through time (even the modern coelacanth is different from the ancient coelacanth). But humans are spread out into many different populations, and have experienced all kinds of different crazy environmental pressures through time and across space. So both logically and empirically we can say with confidence that humans never 'stopped evolving'.
posted by dgaicun at 2:28 PM on February 18, 2006

If anyone's still reading: What are your thoughts on the argument that we 'can't know which animals are sentient or not?'

I put forth that humans are completely unique in their thought processes--another challenges that there's no way of truly knowing.

I'm almost 100% positive I'm right, but I don't have the brain-scans of animals and disserations to prove it. Still, thoughts on this? Any sheer logical reasons why no other animal can think the same way?
posted by Lockeownzj00 at 3:01 PM on February 18, 2006

There is one very obvious way that humans are evolving and I am surprised nobody has mentioned it thus far. This is a classic example of natural selection.

We are rapidly becoming more Arabic, Negro and Hispanic. Successful materialistic Caucasians don't reproduce as quickly. Human evolution is determined much more by reproduction prolificness, than social and cultural advantages of physiological differences. You have to have offspring if your genetic advantages are to be propagated.
posted by DirtyCreature at 3:13 PM on February 18, 2006

Another layman's observation: I think that if we continue to drive in our own vehicles for the next 100 years, the people of the future will become very good drivers. The predominent way that people in modern society don't survive long enough to breed is through terrible driving decisions.
posted by sleslie at 4:01 PM on February 18, 2006

I think that if we continue to drive in our own vehicles for the next 100 years, the people of the future will become very good drivers.

100 years is too short. Not enough generations to weed out bad-driver genes.
posted by grumblebee at 7:23 PM on February 18, 2006

I agree with delmoi: My personal feeling is that without selection pressures we're not evolving. Yes, there is a lot of sexual selection going on, but pretty much everyone is reproducing.

A requirement for evolution is overproduction of offspring, with selection pressure causing selection. Another (missing) factor is isolation.
posted by neuron at 8:36 PM on February 19, 2006

I don't think overproduction of offspring is really a 'requirement' for evolution. Isolation, meanwhile, is mostly important for speciation, which I hope we don't have to deal with.

Sexual selection is a huge factor in evolution. It's not an accident that so many species have sexual reproduction. While not fully understood, it may act to speed adaptation and preemptively eliminate harmful mutations.
posted by breath at 3:54 PM on June 21, 2006