There has been a suggestion that human evolution may have slowed or stopped because of advances in medical technology.
It seems to me that humans are probably evolving faster than ever. For one thing, widespread access to abortions and birth control means that many people who would have reproduced in the past can choose not to reproduce. Or to reproduce less.
On the other hand, with improved vaccination and pediactrics, many people who would have had few surving children in the past are having lots of kids who can go on to have lots of kids.
How could these factors not have a huge impact on human evolution?
To a large extent, we humans create our own environment. Mostly we do that without thinking how it shapes us as a species, but soon we’ll be able to make significant changes to our DNA. Talk about punctuating the equilibrium!!
How does a species stop evolving? The only way I could envision such a thing would be an asexual species in a static environment with 0% transcription errors.
Wouldn’t the only way to test your hypothesis be to compare the rate in the shift of alleles over time? So unless someone did such studies over several generations this is all conjecture.
I think a fact which will have a large effect in the next several hundred to thousand years is that in the modern age it’s easy to find a sexual partner from almost any corner of the globe. There are too many diasporas and and migrations to count. As a fun example, there are more Lebanese in South America than in Lebanon.
I have to applaud this. It seems nearly every time I see some model which strikes my fancy enough to where I look her up it seems she has some exotic parents, like an Arab mother and a Chinese father or some such.
I agree that a full stop is unlikely. But a huge slow-down seems conceivable to me.
From a mathematical point of view, it seems plausible that a species could reach a local maximum, and hover around that point for a long time.
Sure, but common sense counts for a lot. As I said, there have been big changes to our environment that obviously have a big effect on human reproduction. How could that not affect our evolution in a big way?
Sure that too. I’m reluctant to get into it because people are so sensitive to racial issues, but it seems like it’s potentially a lot easier now than in the past for people from different groups to get together and have children. And the mixing is not random.
Evolution occurs when random mutations prove beneficial to survival, giving individuals in a population a leg up on the competition for reproducing. (at least as I understand it in simplified form).
How would this work in a human population? There really is no more ‘survival of the fittest’ for humans. Of course this has only been true for a very short period of time on an evolutionary time scale. Not enough time to affect anything, but what if we can keep it up for 500K years.
Really though, I think the whole point is moot. Soon (on an evolutionary scale) we will be able to manipulate our own DNA. We’ll be able to do in a generation what would take nature thousands or millions of years, or might even naturally impossible.
Either that or we’ll wipe ourselves out, making the whole point still moot.
I don’t think this is exactly right. It’s not so much “survival” as “ability to pass one’s genes on to the next generation” For example, a gene mutation that let you live to 80 instead of 70 but also made you sterile would be unlikely to spread through the population.
On the other hand, a gene mutation that makes you more visible to predators but also makes you more sexually attractive to the appropriate members of your species would be much more likely to spread throughout the population.
(Also, I would argue that in a situation where a pre-existing allele becomes more common due to some advantage it offers, this is evolution too. )
In any case, what matters is “selection pressure.” And what matters to selection pressure is a differential in reproduction – which is not necessarily a differential in survival.
In the case of modern humans, there are huge differentials in reproduction. And those differentials are not random. So it seems to me there’s a ton of selection pressure.
But there is plenty of “reproduction by the fittest”
If we kept it up for 500k years, the whole world would be Orthodox Jews with women who are extremely fertile between the ages of 15 and 50 and who bear a lot of twins and triplets.
I agree that’s a possibility. Personally, I’m skeptical for 2 reasons: First, in order to learn how to manipulate DNA, we would probably have to tolerate a lot of screwups. I don’t think that people are prepared to accept the results of those sorts of mistakes. Certainly not in the West.
More importantly, I think it’s likely that we will have more direct methods of accomplishing the same ends. For example, there’s no need to give your child the genes for being tall if advanced medical techniques can accomplish the same thing. Which is likely to be easier: Giving a person a beautiful face through genetic manipulation or plastic surgery?
One reason a species can evolve is group separation, such that some boundary (e.g., the Himalayas are a form of geographic separation) keeps populations apart long enough for selection pressure to differentiate them. It would seem that human evolution on that particular front is likely to stop.
Whether the group is split up or not, it’s still going to evolve. Separation just allows it to evolve in two different ways. The total amount of change from A to B and A to C is still going to be the same on average.
We have surpassed evolution. We are, for all practical purposes, precisely the same species as we were three thousand years ago, there isn’t enough time for evolution to do its thing. Evolution made us what we were, we made us who we are.
The fact that we’re still the same species doesn’t mean we aren’t continuing to accumulate genetic changes and evolve. Three thousand years isn’t much time for changes to be observed.
I bet that some alleles have become a lot more common in the last 3000 years as humanity has adapted to an agricultural and then a more urban environment. Yes, this is conjecture. But it really does stand to reason.
I would guess that mankind has changed genetically more between 1000 BC and today than between 4000 BC and 1000 BC.
I have to interject here with some comments about evolution of species.
First point: species evolve, not individuals.
Second point: very few traits are controlled by single genes with purely dominant/recessive genes.
Third point: changes in genotype do not always cause change in phenotype.
Fourth point: ‘survival of the fittest’ is part of an economic theory that pre-dates Darwin’s Theory of Natural Selection.
Darwin’s Finches and Mendel’s Pea plants are used to teach about genetics and evolution because they are neat and simple. Things are more complicated than in these two models.
An adaptive change in phenotype arising from a combinations of genes with alleles that exhibit incomplete dominance will not always be passed on to offspring.
An adaptive change that is passed on to off-spring may prove mal-adaptive in an even slightly different environment; since human are social animals, this refers to cutural or physical environments.
Even if a trait is passed on to off-spring, and proves adaptive to the individual, it could disappear because it is so destructive to the community.
Tedious and Childish Example Follows:
Imagine a phenotypical variation for greater body size. This is good for getting more food; you can throw the spear harder and further, you can reach the fruit in the upper branches. Chicks think this is cool and you get lots of action. Guys think you are cool because you kill so many mammoth. Definitely an adaptive change. What happens?
Nothing for three or four generations, because you are carrying two copies of a recessive allele.
The greater-body-size alleles are dominant, you have lots of babies, your babies are big, they have lots of babies, and the immediate environment can not support your nutritional needs. The society crumbles, everyone dies, and this little pocket of the greater-body-size alleles are lost.
The women are too small to birth the greater-body-size infants. Half the women die, the other half won’t go near you, and the only action you get is with the mammoths. Same result to the alleles.
It just seems to me that people often focus too much on mutation rather than simple variation within a population, one consequence of which is to make the evolutionary process seem more like magic than it might.
Of course, but the point is that more evolution did not happen - If you manage to “save” members of population A and then wait a million years, population Afuture will probably be a different species than population Apast.
Haha. But seriously, I think that that “survival of the fittest” is potentially misleading in more than one way. Among other things, it seems to attach a value judgment to the selection process, which I think is a mistake. Because what society values in not necessarily what Darwin values.
For example, suppose that there are 2 alleles: One makes you feel like dropping out of school; getting pregnant; and becoming a single mom with lots of kids so you can collect welfare. The other allele makes you want to stay in school and forego having children until and unless you are married and have a decent career.
Which set of behaviors does society value more? Which allele is more likely to increase in frequency?
The rate of modification from natural genetic drift doesn’t change much.
As the human species becomes able to direct genetic change and no longer depend on natural genetic drift, rates (and types) of modification will change substantially.
Descent is the second part of the equation. In the past, descent (successful reproduction of the organism’s genetic material) has been a combination of fitness for a particular set of existng circumstances, and luck (that the existing circumstances which promoted the successful modification are stable).
To an increasingly major extent the human species also modifies the “descent” part of the equation. We are able to control whether or not we want to reproduce at all, for instance, even if the genes we contain are highly successful modifications. We can also control and direct the external circumstances which would otherwise affect descent. A human may no longer need to be smarter faster or stronger to have a reproductive advantage, for example.
Where all this will take us and whether the net evolution of our species will be faster or slower is a crapshoot. I foresee a fairly proximate future where there is a broad division of humans who have bought into eugenics and have relatively “advanced” descendents, and a second group with “natural” but less capable offspring.
Unless the Big Comet or AGW gets us first and resets the clock for a bit…
