I’m struggling to understand how evolution would still be at work in humans. I understand evolution to work through mutations in genes. The useful mutations increase the fitness of an organism, providing a reproductive advantage, and propagate, while mutations that decrease fitness die out.
Humans have no natural predators anymore and modern healthcare(especially in the developed world) ensures that very few people die of disease before they reproduce. My question then is, through what mechanism does evolution act on (the modern, developed world) human population?
Any trait/gene/mutation that makes us give birth (successfully) more now will take hold over any that don’t. There is nothing different now than before.
Referring to evolution as “working through” anything is pretty near meaningless. Evolution is a process. To the extent that it can be said to “work through” anything, it works through individual organisms.
Mutations are simply one of many sources of diversity within organisms, and a relatively minor one at that. They certainly are not what evolution “works through”.
While that is broadly true, it’s a tiny, tiny part of what evolution is and how it works. For example, you have totally ignored gene interactions, which account for about 98% the “reproductive advantage” that drives evolutionary change. Put simply, statistically you are not distinct from your parents or siblings because of any mutations. You are distinct because of the suite of genes that you inherited and the way that they affect one another. In comparison mutations are trivial in terms of your evolutionary fitness.
We certaily do. We don’t have very many, but that has been true since before our species existed. Predation has simply never been a major driver of human evolution.
You are overlooking the two major points and focussing on the trivial third point.
Reproductive success is relative, not absolute. An organism isn’t competing against other species. It;s primarily competing against its own species. While the population remains at or near carrying capacity, evolutionary pressure is exerted by relative success, not absolute.
Reproductive success is measured by the number of surviving descendants at time t, not by the number of lives births.
Consider an example: the situation 1, 000 or 10, 000 years ago. The most successful men in the world on average produced 8 great grandchildren. The least successful produced, on average, 8 great grandchildren. This is quite easily simply by noting that no lineages were any more inclined to die out than any other, not do do any lineages dominate all family trees. Because disease was rampant, society was unstable and so forth, there was no trait that would guarantee reproductive success. So the relative reproductive advantage of any trait was almost impossible to differentiate from the background.
Today, in contrast, the most successful people, on average, produce 60 or more great grandchildren. And by that I mean certain religious sects that promote large families, deadbeat dads with dozens of illegitimate offspring and so forth. Because all the factors that you listed pretty much ensures the survival and reproduction of all offspring, the relative advantage of some strategies is now an order of magnitude greater than that of alternative strategies.
So clearly evolutionary pressure is at least as high today as it has ever been. In fact it is probably higher than it has ever been.
By exactly the same mechanism as it has always worked in all species throughout the history of the world: differential reproductive rates. So long as some individuals produce more offspring than others as a result of inheritable traits evolution will be occurring apace.
The only way to “stop” evolution is to ensure that every individual produces precisely as many descendants as every other individual. If you haven’t done that then you have not in any sense stopped evolution.
Note that evolution does not lead inexorably to an ideal or even necessarily “better” organisms unless you define better to mean those that have more offspring. So consider some genetic shortfallings like poor vision. Since we have now had glasses for some time, there is not as much selective pressure for good natural vision as thee was before, so the incidence of genetically-caused poor eyesight is presumably greater.
There is similarly less pressure to remove tendencies for diabetes, hemophilia, etc. while the ability to fight smallpox, mumps, measles, polio, etc. is probably also reducing in frequency.
Thanks for noting some of the mechanisms that the evolutionary process follows. While I’m still a little fuzzy on some of the mechanisms you’ve posted, one thing you note seems to be in common with my understanding - Reproductive success is what determines whether a change in an individual organism will persist or propagate and is thus a major part of the evolutionary process. Am I correct?
Now you state that reproductive success is relative, and that I’ve ignored that. I hadn’t. I was, in fact, operating on the unspoken assumption that almost all families in the developed world have between one to two children, and almost all these children survive, thus relative differences are very few. I’m possibly mistaken about this.
Your point,
seems to say that in today’s age the only ‘pressure’ so to speak, comes from people who have lots of kids, and that is, given the way modern societies operate, the most successful strategy around. (in evolutionary terms, and for the time being)
You definitely are. While the average might be 2.5 kids or something, there’s a substantial standard deviation on that number. I know a family who has adopted six children from a 21-year-old, meth-addicted, sometimes-prostitute who is a poster case for why the government should be able to sentence you to mandatory sterilization. Rant aside, this woman is barely into her best reproductive years and she’s already three times ahead of the average.
If elements of her problem are genetic (high fertility, propensity for addiction and poor decision-making, say) then it’s likely that her kids will also out-reproduce the norm. In 100 years, these folks could be up to their 6th generation and out number “normal” folk by 50,000 to 16… and they’ll have the added benefit that the foster/adoption system will have assigned people to raise the kids for them.
That’s…depressing. As an aside, I wasn’t able to find standard deviations for any of the fertility or household size measures. Do they not get reported at all?
I think the reality is somewhere between “normal” natural selection and no evolution.
Of course there is still selection going on; certain personality characteristics are probably associated with having more children.
But evolution typically makes organisms better adapted to the tasks that they spend their time doing: hunting and avoiding predators, building nests etc – as these things are essential to survival and reproduction.
For humans in the developed world there isn’t much that is essential to our survival and reproduction. So there isn’t much selective pressure to make us better at the things that we spend our time doing. We’re not becoming any better suited to our environment.
But of course the whole thing is moot anyway. We’re rapidly changing our environment. Society and technology is moving much faster than evolution could possibly keep up with, even in “ideal” conditions.
However you need to be clear what you mean when you say “reproductive success”. It isn’t a measure of the number of offspring. It’s a measure of the number of descendants at arbitrary time t relative to other members of the same species. An organism can produce 10, 000 offspring and be a hopeless failure reproductively and it can produce one offspring and be an incomparable success, and vice versa.
You are very mistaken. All you need to do to confirm that is look at the difference in fertility rates between groupings a crude as races: White 10/1000, Black 15/1000, Hispanic 20/1000. When you see a discrepancy of 25% even in such crude and large groupings it’s clear that almost all families are not the same.
Just as importantly, even if every single family in the western world had either 2 or 3 children, and one family had 20, that by itself would be more than enough to drive evolutionary change. In fact under those circumstances the change would be even faster than what we see today. The abberant family would dominate the entire planet in the blink of the eye, geologically speaking.
That is almost certainly correct. Not only “have more children” but “have more children and abandon them”, since that immediately frees the individual up for more reproductive activity. IOW at the moment success depend on transforming humans from the ultimate K-strategists into r-strategists.
However this has only been true for the blink of an eye, and of course it isn’t sustainable forth entire species since it relies on the “r”s essentially parasitising the “K”s. Mutual cannibalism isn’t a viable option for any species.
Nonetheless, there are huge differences in reproductive rates between individual humans, and so long as that remains true evolution will continue, regardless of what the actual drivers are.
If and only if there is a genetic basis for addiction, poor decision-making, and high fertility. While there is apparently some genetic risk factor tied to addiction it is not absolute - in that case, biology is not destiny. Drug addicts can be born to non-addictive people, and there are people born to addicts who nonetheless avoid becoming such themselves later in life.
Poor-decision making is even less tied to inheritance. Environment - education, good parenting, and so forth - seems to have a far greater effect on that than genes do. Sure, if you’re born into a dysfunctional family that never insists on school attendance and which has no good examples to follow you’ve “inherited” bad decision making, but those are environmental problems, not genetic.
High fertility may or may not be genetic in origin. A good environment during childhood combined with a lack of inhibitions brought on by drug addiction could account for much of that. Normal humans are actually pretty fertile - even in ancient times means were sought to limit the number of babies produced in many societies. It does no good to pop out a kid every year if down the lie most of them starve to death before reproducing.
As noted, it’s not a matter of how many births, but do you have descendants. To some degree, it’s not even a matter of “how many?” but that the lineage survives long term. People who pour a lot of resources into a few children might or might not, over time, have greater lineage survival than those producing a lot of children but putting less into each one. That, and lineages do not endure in isolation. Low-number/high resource per kid people do marry folks using the opposite strategy from time to time, and vice versa (of course).
Finally, although the modern environment does contain few easily seen predators, and outright starvation is no longer much of a factor at least in the first and second worlds, there are still pressures on people. For example, new diseases arise, and some old ones - such a flu - now travel much more rapidly than before. Also, there are many, many chemicals now common in our environment that weren’t before, and many of them toxic. Any genetic advantage in processing or resisting the bad effects may, in fact, affect future fertility. With more and more people delaying child birth that adds a difference form of pressure to humanity - when most women produced the majority of children between, say, 15 and 35 various things that reduced fertility past 30 had little impact. In places where more and more women shift childbearing to after age 30 that does change the picture and leads to a much different situation that could well affect the averages of certain genes in the population.
The thing is, the changes induced in the above paragraph are not readily visible to the naked eye. A woman who is sterile by 30 due to genetic factors looks no different to the eye than a woman who retains natural fertility into her 40’s - but if both delay reproduction to after 25 (never mind 30) the number of descendents each leaves behind, even in today’s world, may be very different.
An organism’s environment is wherever it lives. Better suited means more reproductively successful and nothing else. So long as evolution through natural selection is is occurring then a species is, by definition, becoming better suited to it’s environment.
Unless you are arguing that there are no longer any heritable traits whatsoever that increase reproductive success, then your above statement is utterly incorrect.
No, of course I’m not saying that, and I’m surprised at your reply as you seem to be ignoring things that I said. I said that selection is still happening.
And I’m not making the mistake of believing evolution is about “progress”.
The point was this: most animals spend all their time either doing things essential to their survival or reproduction, or resting. So over time they may evolve physiological changes to make them better at doing that stuff.
Meanwhile, like most people in the developed world, virtually all of my time is spent expending energy on things that aren’t essential to my survival or reproduction. There’s little selective pressure to become better at these things.
So while we of course can say that humans are still evolving, we should be aware that some of the implications of natural selection don’t apply to us. Evolution of humans going forward is likely to be very different to other animals and even human evolution up to this point.
As for the statement being “utterly incorrect”, note that I was not speaking from an evolutionary perspective in that line. Our very existence implies we are well-suited to our environment, in that sense.
I was purely making a personal value judgement. To me, being better suited to my environment would be being better at the things that I spend my time doing, not being better at not bothering to buy condoms.
The above discussions have covered all the basics…
In Western first-world countries we have seen a dramatic demographic shift. Economic circumstances are such that we are below replacement levels. Only immigration helps prevent the population from actually shrinking; once mortality catches up with demographics and all the baby boomers start dying off. (Of most of the families I know, few grandparents have 4 grandchildren, let alone 8 great-grandchildren for the ones at that age… It’s all collapsed in the last 2 generations.)
There’s the obvious backward eveolution pressures as mentioned. Strength, good eyesight, disease resistance, lack of chronic conditions like diabetes, asthma, etc. - these are no longer evolutionary advantages. Of course, the main question is - are they in some way genetic? Perhaps we are selecting for the “foolme once” deadbeat dad type of male?
The other problem is that the economic conditions make it such that the “winners” don’t have children, and the “losers” do in our economic rat race. Whether its deadbeat dads or crack addicts, or more prosaically, the welfare/minimum wage poor vs. high achievers; the richer people stop at 0,1, or 2 kids and the poor don’t (usually!!! Our old friend, statistics!). So in the long run, we are selecting for underachiever. This all depends on whether, again, there is a genetic component to this situation. Latest research on intelligence is all over the map and generally designed to serve agendas, but figure that intelligence is 50% earned and 50% inherited, and intelligence plays a decent role in whether you flip burgers or flip real estate, then we are in the western world, selecting for stupid.
OTOH, such pressures are 100% different in the developing world where much of our immigrants come from, so no surprise if their kids are the bright ones. As for the evolutionary pressures in a semi-developed country like China, or a wild-west bad dream like Russia, who knows?
And of course, it’s only been since, let’s say, about the 1920’s - so at most 4 or 5 generations; how much evolving can happen with relatively minor pressure over such a short time? The pressures on reproduction in the computer age may be completely different than in the industrial age. The Freakonomics author made the point that a huge number of crack babies and unwanted children, this generation’s criminal element, may have disappeared due to the availability of abortion over the last few decades. OTOH, birth control “oops” does not according to his stats select for those genes. Women have the number of children they plan to have, an birth control failure just means they have them earlier.
I’m pretty sure there still are evolutionary pressures today. For example, changes in diet, which have in the past caused changes; for example, cooking made it easier to chew food, so our teeth and jaws shrank, as well as easier to digest, leading to a smaller digestive system and, along with increased meat consumption and foods rendered non-toxic by cooking, enabling larger brains (many modern foods made with with simple processed starches and sugars are probably even easier to digest).
Many people are also much less active today than their ancestors were (even people who exercise daily for an hour or two, which is different from working all day long just to survive), so this may lead to a reduction in muscle mass over time and possibly, a reduction in the urge to eat/amount eaten, eventually leading to less obesity.
I’m not quite sure what **Mijin **means with that particular quote, but we are the only species in the history of earth that has been aware of genetics or evolution, and that’s a game changer. I think that’s what her next sentence was going after.
If we wanted, we could artificially create selective pressure. Or artificially preserve traits that natural selection would otherwise remove (which leads to a semantic argument, I realize. If we decide that really big earlobes are where it’s at, even though they don’t provide any advantage, and in fact occasionally lead to fatal earlobe infections, then one could still make the argument that big earlobes are natural selection at work. One could also make the argument it’s an artificial pressure).
I’m aware I’m responding to a fur-real scientist, and I’m not trying to front, or nothin’. Doesn’t awareness of evolution move the game up to a meta-level, though?
Simply being aware of the game doesn’t mean we can remove ourselves from it. We can add some “house rules”, but we’re still playing the same game as every other species.
Creating or modifying pressures doesn’t change the mechanisms driving our evolution, however. Whether those pressures derive from internal or external sources doesn’t really matter in an evolutionary sense. Even a sustained and determined eugenics effort would only succeed in changing the selective pressures - natural selection would still be occurring alongside any artificial selection (just as it does with species we’ve domesticated); variations, heritability, and differential success as a result would still be the rule.
I’m not a fur-real scientist, actually. Just an interested amateur.
And as I said above, awareness of the game can give (and has given) us awareness of the rules, but we still can’t get out of the game. We can tweak the rules, but the underlying mechanisms which drive evolution will still be there, regardless of how much tweaking we do. Changing the selective pressures will not change the way evolution works, or whether natural selection will continue to function. All we’ll have done is change the selective trends.
But, beyond that, not all humans are subjected to the same pressures at all times. Many humans in “the West” don’t tend to have to battle starvation and malaria and brain-eating ameobas and man-eating tigers to the extent that other human populations may have to. Thus, even if we (“the West”) are able to suppress some pressures and accentuate others, that doesn’t mean that the average genotype or phenotype for the species will necessarily change in a way that is best fit to our particular environment.
My point in all of this is that there is little we humans can do that will make us exempt from evolution via natural selection. It’s a process, and it doesn’t go away just because we change our environment. And, unless we make universal changes such that all humans exist in the same environmental circumstances, anything that can be said about one population’s selective pressures will not necessarily apply to all human populations, thus one cannot infer anything about the overall future of Homo sapiens based on what’s happening here and now.
I would suggest the game-changer is that we can select whether or not to reproduce, and even after the fact, selectively abort undesirable traits. We can test for certain bad genes and prevent them from being passed on.
However, yes, there are certain evolutionary selection processes we cannot escape. You can also argue that certain traits - i.e. being smart enough to cross the street safely - are also selected for by our modern environment. Child care where the children are confined is less of an issue in a situation where the biggest danger outside your door is wandering goats.
Also, keep in mind we are talkin differential reproduction as the main driver to evolution. Susceptibility to cancers after your child-bearing years, for example, is not a significant evolutionary presure.
No, my point was actually trying to summarise the stuff I’d already said.
Let me try again, from scratch.
Often in discussions of present-day human evolution, someone demonstrates how selection is still at work, and then concludes “so nothing’s changed”, “we’re still evolving” etc.
I think that is misleading.
If we see an organism consistently expending energy on an activity, it’s a pretty safe bet that it contributes to their survival or reproduction (or the survival or reproduction of the group). Alternatively if it’s something redundant or harmful, we’d expect it to get selected out over time. This rule of thumb won’t work in studying modern humans.
Likewise, changes to a species’ habitat will often (not always) lead to changes in the species. Humans however, tend to work around such things with technology and/or knowledge.
Both of these exceptions are pretty much unique to humans.
Now, these “rules of thumb” aren’t actually part of the ToE. Which is why I picked my words carefully – I said implications of natural selection.
As for the evolutionary pressures in a semi-developed country like China, or a wild-west bad dream like Russia, who knows?