Speed of Evolution in Humans

This is a factual question based on a fictional source.

I was recently reading a Star Trek novel that Implied that the Remans and Romulans evolved from the Vulcans in only two thousand years, which seems a bit improbable.

Humanity as far a I can tell has not evolved significantly in two thousand years. Admittedly average height has increased, but this is probably due to better nutrition than evolution.

So my question is how quickly could humans adapt to a different environment?

Will light skinned humans who now live in hot sunny countries have descendants that will have darker pigmentation? Similarly will darker skinned people in countries with lower levels of sunlight tend to have lighter skinned children or once we have developed a defence do we keep it?

BTW please don’t think there’s any racial or eugenics slant to my question, these were just the first examples that sprang to mind.

As an additional example assuming humans created a martian colony, how soon would we adapt to life in a lower gravity environment and what would be the likely adaptations?

Romulans and Vulcans are not separate species - they are fully inter-fertile, for example. They’re more like two races or two ethnic groups with some physical differences.

Some degree of divergence is not unreasonable in two thousand years

Define “adapt”. Humans born and raised at sea level can adapt to much of the Tibetan highlands, to the extent of being able to work, live, and reproduce. They aren’t as well adapted as native Tibetans, but they do adapt to the new environment.

There’s a variation in skin tone in any human group. So far as I know, there’s no bar on dark skinned people evolving lighter skin and vice versa. However, such genetic changes take thousands, if not tens of thousands, of years.

Humans adapt just fine to lower gravity in the sense of being able to work, being comfortable. Problems come in, in that muscle strength decreases and so does bone density. Live on Mars a couple decades and by Earth standards you’ll probably have some osteoporosis. Which may not be a problem in the lower gravity.

More problematic on Mars is the increased radiation and the dust. A more efficient DNA repair mechanism might be a good adaption. And Martian dust is exceedingly fine, it’s going to be everywhere and the particles are small enough to cause real havoc in the lungs - adaptive changes to handle small particles would be good there. Of course, the Martian atmosphere is exceedingly thin - I’m not sure terrestrial mammals have the capacity to adapt to breathing it, even after a few million years. Unless the planet is terraformed we’ll always be dependent on advanced technology to survive there.

Yes, but only if:
-Mutations arise causing some of the children to have differently-coloured skin from their parents (reasonably likely)
-Those children experience a statistically increased level of reproductive success.

Evolutionary variations involving levels of sunlight or heat aren’t going to ever occur again amongst humans. Well, not as long as we’re Earth-bound anyway. Populations are simply too mobile for them to be consistant enough a factor.

So in order for a vulcan to evolve into a 2.5m tall photophobic with fangs due to evolutionary pressure it would be necessary for being bigger and having eyes that see better in a low light environment to produce an advantage in breeding.

How many generations though would it take to evolve from an average height of say 2m to an average height of 2.5m?

Back to real humans though, my Mars question was assuming something like living in a modular construction similar to those already experimented with by NASA. The first generation would loose bone mass and their hearts would shrink, but these are just natural adaptations due to the body aclimatising (sp.) to it’s new environment. Would the offspring of the first generation settlers be adapted to this envirnment perfectly? and how many generations would pass before it was not possible for a martian sub-species of humans to be unable to physically support themselves on the earth?

No; it sounds like you’re labouring under a misconception about what evolution is - it works because the forms that are better suited to their environment typically enjoy better reproductive success than those that are less suited; over many generations, the genes of the more-suited forms come to dominate the gene pool. The adaptations don’t happen directly because of the environment; environmental pressures merely select those traits that happen and are beneficial.

Of course the other possibility is extinction - if the change in environment is severe and abrupt, nobody enjoys much reproductive success at all and the whole race dies out.

The “Adaptations” you describe are of individuals, not of a species. Someone born on a planet with low gravity would certainly develop differently than they would have on earth but there is no reason to think that that person’s child would not develop normally if sent back to earth.

As for generations from 2 to 2.5m height. We don’t even have a 2m average height now but for the sake of argument we’ll stipulate that. The number of generations could probably be calculated by by the environmental pressure to be tall and the distribution of gene markers for exceptional height in the population. What pressures are there now? Lucrative NBA contracts? That doesn’t stop short people from having kids. I doubt if there could be much pressure to evolve without artificial conditions like selective breeding and sterilization of those withou
t the right genetics. It can work remarkably fast in animal populations as long as you can identify the traits you want.

The crucial point about evolution is that it requires isolation to bring about diversity. Given the enormous international mixing which modern society makes possible, humans are currently about as diverse as they are ever going to get (barring the isolation consequent of space colonisation or something).

It’s estimated that Homo floresiensis went from roughly 2m to roughly 1m inside of 100k years. Although we don’t know for sure, I’d guess it was closer to 10k than 100k.

We really don’t know, although I can say with certainty that the first generation would not be “perfectly adapted”. We’d most likely have all kinds of technology that would make environmental adaptation unnecessary. You’d still get genetic drift, though, so eventually (on the order of 1 millions years for humans?) an isolated population would no longer be able to breed with the original population.

In the case of a Martian colony, the environment would be mostly controlled, but there’s nothing we can do easily about the gravity. Folks living on Mars would spend most of their life at a third of a g. Then, too, the very artificialness of the environment would be another effect: You wouldn’t be spending much time, at all, out in the Sun, and what time you did spend, the Sun would be a lot dimmer.

For the first generation of colonists, they would probably be getting less exercise than their Earth-bound brethren, due to the lower gravity. So, just like any human who doesn’t get much exercise, they’d probably lose bone density and muscle tone. But they could probably get it back, if they tried, with a system of heavy exercise. Likewise, you wouldn’t see much tanning, unless the colonists deliberately tried for the look using UV lamps (like in a tanning parlor on Earth). So the colonists would have paler skin, on average, than us Earthworms.

The first generation of children born on Mars would have similar effects, but probably more extreme, since they’re exposed to Martian conditions for their whole life. The lower gravity might have some significant changes to development, as well: It’s conceivable, for instance, that a kid growing up on Mars might grow considerably taller than he would have on Earth. But their genes still wouldn’t be different. If a couple of second-generation Martians (with their pale skins, weak muscles, and long, brittle bones) came back to Earth and had and raised a child here, that child would be a perfectly normal Earth-type human, with strong muscles and bones, and as much of a tan as anyone else.

All of this thus far is just individual adaptation, which is not the stuff of evolution. Where does that come in? Well, occasionally, a child is born with some mutation. Most often, the mutation has no immediately significant effects: The kid might have a different eye color, for instance. But suppose that we have a mutation which slightly changes the structure of the heart, perhaps. This mutation, please note, would be equally likely to occur on Earth or on Mars. Now, it may happen that this slightly changed heart doesn’t work very well in a full one gravity. It may not even work well at all in one g, in which case, any Earthling child with that mutation is likely to die very young before having children of their own. But it may be that this same mutation makes the heart work a little more efficiently in one-third g. So a Martian kid who had this mutation might be a little healthier. Maybe he’ll be enough healthier that he’s a little more likely to survive accidents and reach adulthood. Maybe it’ll help give him a little more athletic ability, which makes it easier for him to catch the eye of girls. And maybe he’ll marry late in life, after his peers are dying of heart attacks. In short, maybe this mutation gives him some slight edge in reproduction (of course, maybe it doesn’t: Evolution doesn’t care if you live a long and prosperous life, as long as it doesn’t affect how many kids you have).

Well, if this mutated heart does give some slight advantage in Martian gravity, then the lucky guy born with it will tend to have more decendants than his peers. And those descendants are likely to have the same sort of modified heart, and enjoy the advantages of it themselves. Gradually, the gene for the modified heart will become more and more common in the Martian gene pool, and it may happen eventually (if there’s not continual immigration of new Earth-type humans) that there are few or no Martians left who have an Earth-type heart. Meanwhile, there have been many other mutations, a few of which are also favored more on Mars than on Earth, so Martians might on average start to tend to have a different bone structure, or muscle structure, or skin composition, or the like, than their Earthly cousins. If enough of these changes occur, then the Martians would eventually become unable or unwilling to interbreed with Earth humans, and we’d have a separate species.

Generally, no. People living in more sunlight do tend to have their skin turn darker (called ‘skin tanning’). But this is a surface reaction to sunlight; it does NOT change the genetic material that they will pass on to children.

In the same way, a person blinded in an accident will produce sighted children; a soldier who loses an leg in battle will still produce 2-legged children, etc.

Changes in your body that happen after your birth do not affect the genes you pass on to your children. Believing otherwise was a hallmark of the thoroughly disproven Lamarkian genetics theory.

Evolution of a species happens when random changes in genetic material produce children who, because of this change, have a higher (or lower) advantage in reproduction or survival. Mangetout explained this pretty well.

That’s not the question which was asked.

It’s been estimated that took about 10k - 20k years for skin to evolve from dark (eg, African tone) to light (eg, European tone). But it’s also thought the original folk who left Africa for Europe and Asia were not as dark as most modern sub-Saharan Africans. They may have been more brown-toned, like the Khoi-San people of Southern African today.

That timeframe probably still holds true for evolution in the opposite direction. But that also assumes no significant technology impeding the necessity of a genetic change-- eg, sunscreen for light skinned people in the south or Vit-D suppliments for dark skinned people in the north.

It could easily be just one generation, or it might never occur. It all depends on the phenotypic spread of the population, the genetics behind the expression, the relative importance of genetic vs. environmental factors, the strength of the selctive pressures etc.

Imagine a scenario in which your species has an average height of 2m but with considerable spread, so that half the population was either over 2.5 metres or under 1.5 metres. And lets also imagine that in this species height is entirely genetic and not based at all on nutrition or othe renvironmental factors. Now if a disease goes through tommorow and selectively kills 99% of the people under 2 metres that species will have evolved from an average height of 2m to an average height of 2.5 metres overnight. It’s certainly plausible for such an evolutionary change to occur within one generation.
Alternatively imagine your species has an average height of 2m but with very little spread, such that 99% of people are between 1.95 and 2.05m and less than 0.001% of people are over 2.5m. Also imagine that the species height is, like humans, controlled largely by nutition rather than genetics. Now expose this species to a disease that kills off 10% of the people under 2m. We could keep doing this every generation forever and the species will never evolve to an average height of 2.5m. Despite a strong selective pressure for greater height the natural variation isn’t high enough and the genetic control of height isn’t suffiecntly selctable to have any effect at taht selection rate.

Note that in the second example it’s conceivable that we could get the desired increase given thousands of generations, but it’s equally plausible that we never will because height of >2.5 metres simply isn’t geneticaly dictated and therefore can’t be selected for.

I have a theory that human evolution on earth is grinding to a halt.

Evolution works due to mutations that lead to fitter beings. (Fitter in the sense that they adapt to the environment better)

Given that humans control their surroundings, there doesn’t seem to be a need for adaptation.

For example all lions look more or less identical. Humans on the other hand live long lives despite genetic diseases due to medicines, health care, etc. thus passing on defective genes that would otherwise be weeded out in the wild.

Not necessarily. A lot of evolution happens just through changing of the frequency of existing genes, or recombination of existing genes into new linkage groups. Although mutations are the raw material for evolution, new mutations are not at all necessary for significant evolution to take place.

Selection is *different * for modern humans, but it hasn’t gone away. Relaxing selection pressure can cause evolution, just the same as imposing it.

Not to other lions

That means only that, in our new environment, those genes are no longer as defective as the used to be. This is also an adaptation to environment, and a kind of evolution - not “evolution grinding to a halt.”

Most organisms control their environments. Humans aren’t in any way unique there. Some, such as termites, control their environments far more than humans are capable of. Are you suggesting that evolution has stopped for termites?

At presents something like 10% of the human populationis at risk of dying or being rendered effectively sterile from just one disease: HIV. Somehting like 80% of people are dying from ither cancer or herat disease. We may be controlling our environment but any gene that is beneficial for just one of those factors has massive potential evolutionary benefits.

The idea that the limited human control of the environment negates all selection pressures is clearly not true.

You and Larry Niven. :rolleyes:

Natural selection hasn’t quit working its wiles on us any more than it has on the domestic dog. However, our deliberate intervention has created additional, artificial pressures which act to direct selection; for instance, owing to the importance of spoken communication in modern society, we’re (presumably) gradually selecting for more verbose and witty people. Women look for “a sense of humor” in a man, and mimes don’t get laid. (At least, we hope they don’t. I’d like to think that they’re an evolutionary dead end.)

However, because we (of developed nations) are more than adequately fed, and because we have flashlights to help us see in the dark, cars to transport us great distances, et cetera, the selective pressure on most physical attributes has been attenuated. There is no reason we would, for instance, develop insanely long necks in order to reach food on high shelves (well, except for Giraffe); we simply pull out a step-ladder. Selective pressure for height by means of nutritional sustainment are thus eliminated.

We have, evolutionarially recently, undergone selective pressure based upon disease resistance, much to the lament of the aboriginal Americans. Those of us fortunately to be the descendents of those who survived the winnowing effects of smallpox and other common diseases are examples of “descent with modification”, as Chucky D would have put it. Today, however, with the pharmaceutical companies spiralling ever closer to an ability to not only stimulate the body’s natural defenses to fight infection but to tune substances to directly attack viral and bacterial invaders and contribute to the body’s hormone balance but to actually add to and bolster the evolved mechanisms for biological defense, we are coming closer to a Lamarckian definition of evolution; creating and “passing on”, either by chemical supplement or gene therapy and intentional selection/modification, acquired charactistics.

Selective pressures still play a part, of course; we are just directing those pressures to a particular end–say, being a better tool user, or a better communicator–rather than being invariably subject to whatever the natural ecosystem throws at us.

Just wait until the “breast enhancement gene therapy” comes out. Memetic sexual selection will result in a completely unwieldy form that future taxonomists will be wont to explain. “Well, maybe it had something to do with heat dissipation. Or perhaps they had to provide a high protein diet through adolescence. Possibly they were ancillary central nervous system clusters to cope with the additional complexity of the maze-like “suburban” environments they frequently habituated.”


Well, I did say it was just a theory.

Actually I was responding generally to the OP:
“So my question is how quickly could humans adapt to a different environment?”

It’s true we are evolving to artificial pressures, but given the OP’s question about Star Trek beings I assumed s/he was asking about evolving in the broad sense of the traditional manner, mamals, primates, humanoids.
In other words, towards a ‘better’ human (stronger, smarter, etc).

Given the question, I still stand by my theory.

(Theory, as in layman’s term)

Thanks for all the interesting responses, it seems that I was confusing individual adaptation with evolution.

Consider my ignorance fought (at least on this matter).

But it seems like everyone can procreate with everyone on Star Trek. There’ve been Vulcan/Human hybrids, Romulan/Human hybrids, Romulan/Klingon hybrids, Kingon/Human hybrids, etc.