The Animal World & Natural Selection

Watch any television program on wildlife and one inevitably hears this commentary: “the fe/male [lion] seeks to mate with the strongest fe/male so as: (a) to pass on his/her genes” or, (b) “to ensure that his/her offspring have maximum advantage in the wild.” This implied deliberation on the part of animals baffles me. What is the commentator really saying?

While this biologic selectivity makes sense to animals capable of higher-order cognitive functions and who may possess a rudimentary grasp of genetics, I find it difficult to believe that non-human animals have even an intuitive understanding of the consequences of their mating with a presumably inferior mate. (Though I will readily concede the social aspect.) Also, what understanding might such animals have of the consequences of their not producing offspring at all? (And what might those consequences be?)

Can a male or female animal really know that procreating with a somewhat biologically “inferior” mate will diminish the prospects of his/her offspring succeeding in the wild—or that another potential mate might produce somewhat better traits? Again, this would imply sophisticated cognition that seems well beyond the non-human realm. Or, is it more the case that stronger, fitter animals acquire higher social prominence, and that potential mates are instead attracted to this social prominence (and the advantages it confers), which ultimately—but not deliberately—leads to superior offspring? My understanding of the animal world (forgive the term) is that the males are sexually “promiscuous,” which leads me to conclude that perhaps the real driving force in the male mind is one of sexual gratification. But how to explain the female?

To what extent do you think this genetic selectivity applies to human behavior today compared to, say, 25,000 years ago? And how is that biological advantage generally measured—intelligence, physical size, fitness, wealth, emotional stability, build, altruism, morality? (Obviously demands re: these traits varies from person to person.) Generally speaking, can we assume chronic alcoholic, severely diabetic, psychotic or morbidly obese persons have a strong biological imperative to pass on their genes? Why would nature be interested in this? Or is it mainly about sex—that we want to mate with the most attractive and socially prominent—and the consequence ain’t exactly well planned? Lots of circular reasoning here.

Long? Yes. Dumb? Obviously. This is waaaay outside my field, folks. Don’t go completely berserk, but a little razzing will probably make you stand a little taller, so what the hell.



Exactly what you thought. All species have some ways of deciding whom they want to mate with, and these attractions have to do with genetic traits which a parent would want in their offspring. All animals do this. Even humans do this. It’s not vanity (exclusively at any rate) that humans find certain traits to be good in a prospective mate.


What gives you the idea that some of these animals are not capable of “higher thought,” and even if they aren’t, why does doing calculus make a species any better at deciding who they want to have kids with? That’s the only instinct at work here, you know. Who gets my seed, whose seed do I want. And every species has a criteria they want to meet. We’re lucky, actually. Even ugly people get laid occassionally. For many animal groups, the same cannot be said.


Maybe not in so many terms.

However, a female ram will mate with the male ram who just kicked everyone elses ass with their head-banging. Why? Because they just know that it is far more likely that a strong male will get her a strong child to help propegate their species than ifshe takes the pitiful ram whose horns fell off.

Genetics shows us she hedged her bets, but with an inate ability to make this correlation, she didn’t need DNA testing to figure it out.

And I just picked one species and one trait out of a hat. You can take the fish that picks the brightest and most colorful fish as a mate, or any species, really.

I think humans are the only species who will fuck anything, really.

Ultimately, it seems to me you are putting a lot more into the ability to find an attraction in a mate than you need to. As the song goes, birds do it, bees do it…

Yer pal,

OK surfer, why don’t you pose an easily decided question for a debate next time, like ‘does God exist’ or something.
But seriously this isn’t a dumb question, it just seems kind of mixed up between the ideas of evolution/natural selection which have absolutely nothing to do with choice, purpose or thought, and the whole mother nature thing which implies direction.

He’s trying to say, rather poorly, that there is an instinctive response in the female to choose the male whose genetic fitness is highest. This is certainly no more conscious in animals than it is in humans. I’ve never found myself looking at an attractive girl and saying “Hubba hubba, that’s one great set of chromosomes’. We are genetically pre-programmed to find certain traits attractive, and these traits are usually closely matched to reproductive fitness.

I have seen virtually no evidence that humans understand the consequences. We just devote most of our attention to the most attractive potential mate and the less attractive fall into second place. Animals do the same.

There is no evidence that animals have any understanding of the consequences of not having young that I have seen. Animals probably don’t have sex to have young as some humans do, they have sex to have sex. Offspring are a by-product. They choose their sexual partners based on attractiveness with no thought that this attractiveness corresponds to reproductive fitness. As for the consequences of not having young, this can vary from no consequences at all for some species, to death for others (certain polecats die if the don’t fall pregnant) to an increased lifespan for others (some male marsupials expend so much energy fighting, displaying and mating that they die of exhaustion within days of copulation).
From a species viewpoint the consequences of any individual not having young will be a dilution of the gene pool.

Probably not. But this is irrelevant. If you are attracted to someone then you are attracted to them. The attraction is programmed in because it correlates very strongly to reproductive fitness. You don’t actually think about it, and neither do animals. In the same way that if you were to meet two potential mates at the same time you would devote more energy to the one you found most attractive, so an animal faced with the same choice will do the same thing. It’s not a case of ‘procreating with a biologically superior mate’, just a case of putting the moves on the redhead instead of the blonde.

Only if you assume choice rather than simple attraction. If you just think of it as ‘animal magnetism’ at work it suddenly makes much more sense.

This is possibly part of the explanation, but there are many other factors at play. Certainly social prominence is important in some species, in others it is purely and simply fighting ability and in still others display capability. In most animals it is a combination of all these and physical fitness and health, disease resistance ability, food gathering capability and intelligence. Potential mates are attracted to all of these in varying degree depending on their innate programming.

Basically the promiscuous male thing is true, but there are huge numbers of animals of all types that form monogamous pairs, or where it is the female that is promiscuous. The sexual gratification thing is true of all animals, whether male or female.

To the same degree if not more so. The pressure is for women to be smaller, prettier, thinner, younger looking and generally give the appearance of being more like a very young woman able to reproduce for many years to come. The pressure is on men to be bigger, stronger, taller, richer, more muscular and generally able to provide for and protect offspring and mate. If popular media images are anything to go by this genetic selectivity is accelarating, not decreasing. Very little attention is devoted to intelligence, altruism, ethics or other more cerebral characteristics in popular media for either men or women. Apparently far less than was so historically. So I’d have to conclude that genetic selectivity is very, very important to humans.

And how is that biological advantage generally measured—intelligence, physical size, fitness, wealth, emotional stability, build, altruism, morality? (Obviously demands re: these traits varies from person to person.)

For women it appears to be measured in number of child-bearing years remaining: appearing as young as possible while still being post-pubescent. For men it appears to be measured in capacity to provide and defend: being large, healthy and wealthy. Morality etc. seems to be of less and less importance as time passes. Of course you’re quite right that this varies between individuals, but popular literature etc. probably gives a general view of social values.

Of course they would. All animals have a desire to pass on their genes, and almost all humans have some desire for children. Just because you have a ‘defect’ doesn’t prevent this. Nature isn’t interested in this one way or the other. Nature isn’t a thinking force, it is an abstract concept, as is evolution. As for what the evolutionary advantage might be, that is a two-part answer.
Firstly there is no easy way to prevent an organism from reproducing once it has a trait that may inhibit surviveability, genes just don’t work that way, so the question is actually moot.
Secondly who is to say that any of the traits you list above aren’t actually of survival value under some circumstances. Given their prevalence in most societies I would have to say that they do confer some survival advantage some of the time, we just aren’t sure what… The classic example of this type of detrimental survival trait is sickle cell anaemia. This genetic disease causes red blood cells to collapse when they are placed under stress. This impairs their ability to transport oxygen and so could be considered a liability to those who possess it. If there were a some sort of genetic feedback whereby those who carried negative traits were prevented from breeding, as you suggest above, then all those with this trait would be rendered sterile. However the sickle cell gene also causes blood cells to collapse when infected with the malaria parasite, killing the parasite and preventing serious infection. Since malaria kills more people in some areas than lack of oxygen the trait becomes beneficial overall and is passed on. It is possible that alcoholism, diabetes etc. may all have similar survival advantages.

Nope, that’s about it. It feels good so we do it. It is a little circular, but only because it’s an example of a positive feedback loop.
Allow me to illustrate it this way.
Women have developed wider hips in order to facilitate childbirth owing to our upright posture. Wider hips conferred a survival advantage on a woman’s offspring, therefore wide hips have become sexually attractive. A survival trait has become attractive because it was a survival trait, and all those who found it attractive selected ‘better’ mates, and had more young who also found the trait attractive etc. I’m sure that at the same time wide hips were developing some proto-human was getting into a foot fetish as well, but selecting a mate based entirely on her feet didn’t do much for his survival chances, and so his line died out.

Oh, and Satan. Humans aren’t the only animals that will ‘fuck’ anything. The males of most species of mammal will have sex with any available female. The females tend to be a little choosier, but this may be simply because for most animals sex = offspring. Humans don’t have to worry about this so much.

Natural Selection is VERY complicated. Among, say, the higher mammals, a number of things come into play (and I’m certain to miss some). Your idea on social prominence is well-founded. Also, the less desirable traits are the ones that hinder survival, so the healthiest animals are more likely to mate. Some animals select for traits such as colour of plumage or prominence of some feature, whether these matter or not. It may even be possible that animals who are successful in, say, hunting gets associated with food, and that this is selected for. I read about a bird species, the males of which compete for mates by buildng the best nest possible. You name it, animals select for it. Consciously? Probably not in the human understanding. But if a cat can associate the sound of a can opener with food, then why can’t a lion select a strong body with mateworthiness?

On selection in humanity… It may be argued from a number of perspectives. There is tremendous variety, for certain. Some select for social status and physical attributes, others select for personality, others claim to select for personaltity, others mate late out of fear of loneliness, others never mate.
Alongside the classical answers, let me suggest that the outcome of human selection may (in part, of course) be psycologically determined. A human with high confidence will be more socially successful (in general, and within limits), and be more easily selected for. A human with poor confidence might sequester her/himself from society, by bieng a recluse, a ‘loner’, whatever, and even ask him/herself ‘Do I deserve to be selected for?’ and similar questions. This may seem an extreme case, but how many people have had trouble getting dates because of their isolated social position, shyness, or lack of confidence?

This second (human) debate is much more difficult to resolve, considering the wide range of physical, psycological and social phenotypes among humans.

It is difficult to make accurate generalizations about human society (especially since observations are best made from within it!).

Since all the good evolutionary points have been made already, but I still have these two cents here, I’ll toss in a minor issue. The OP states

There’s a confusion between higher-order cognitive functions and the ability to act in a beneficial or “intelligent” manner. Natural selection has “designed” organisms that make good mate choices by weeding out those that make poor choices. The ability to make a good choice is present as an instinct or a desire, rather than a conscious thought. It’s very likely that humans are also responding to instincts or desires, and the conscious “choices” are just rationalizations that our minds make up to explain our desires to ourselves. But my point is, the intelligence is innate – it exists implicitly in the design of a machine built to make good mate choices, which is different than it existing in the mind of an organism.

An analogy. There’s a lot of calculus involved in the ability to predict the path of a baseball that I’ve thrown to you. However, you consciously don’t have to know a lick of calc to put your hand in the right place. And, there probably isn’t a module in your brain where some cells are furiously solving equations. You ARE solving a calculus problem, but not in any way your conscious mind would recognize.

Anthropomorphizing, saying an organism (or natural selection) “wants” something, is a convenient shorthand for talking about these complex ideas. But it easily produces the confusion that you experienced watching your nature show.

I would dispute this as well, at least in that your brain where cells are furiously solving equations. The brain may very well be constructed to give calc results from visual motion stimulus.

There are many circuits which are constructed from op amps and a few resisors which solve second order differential equations. The circuits aren’t complicated, its the understanding behind them which are.

I got nuthin on the evolution/natural selection debate.

Point taken.

I shouldn’t have made it sound like there is no calculation going on. Clearly your brain is solving the problem of where the ball is going to be. I was just trying to emphasize that the solution isn’t being arrived at in the same way we’d solve it consciously.

As you point out, the understanding is the complicated part, and that understanding isn’t really present in how our brains solve the equations. Or it is, but only implicitly, which is once again my original point that I’ve now beaten into the dust.

Um, what were we debating again?

No discussion of this type would be complete without a link to this Onion article:

All animals have traits that they look for in a mate. They are always in some way designed to help make a better offspring.

Well, I would wonder what about homosexuals? What are they attracted to in a mate and why?

Actually, a test of this kind might provide evidence either way as to whether homosexuality is indeed genetic or choice.

In testing heterosexual human beings, the things that most people find attractive in a mate - things such as youth, being proportionate (both height-to-weight and in other ways as well), in good physical shape - seem to me to be the same things that gays are (as a whole) attracted to.

(Please don’t come in here taking offense and saying you like old fat people. I’m sure you do, really. Hell, my fiancee does! :wink: We’re all different. I’m talking about averages and trends, not the be-all end-all.)

I would be interested in seeing the same tests that I’ve seen given to straight males and females to determine what things most attracted people and applying the same test to homosexuals and seeing if there’s a difference.

My hypothesis would be, there isn’t a difference, and I would say this based upon my own unscientific observations. And I would say that this is the case because ecen though homosexuals (and in most cases, heterosexuals, for that matter) are not having sex to procreate, but for pleasure. However, the same drives kick in in all of us because we’re all wired the same way that sex = procreation subconsciously.

If this were true, I would surmize that homosexuality is even more likely than we think now to have some kind of genetic link because if they are viewing the same things attractive in a mate as straight folks are (just looking for the same gender instead of a different gender), it shows that their sexuality is not as different from heterosexual people as some people would think.

Please don’t think I am gay-bashing here. Those who know me well I think would know that ain’t me. But I wonder if a similar study has ever taken place and what the results were?

Yer pal,

Well, Satan I hope that those were all the serious answers the OP was going to get, because I can feel a hijack coming on.
I’d be highly surprised if homosexuals and heterosexuals didn’t find basically the same things attractive in potential mates, since as you surmise it probably stems from the same instinct.
I’m just not sure what this would contribute to the genetics/environment issue. Either way homosexuality stems from the same root cause (heterosexual sex), and is a modification of the original process. Whether that modification is due to genetic or environmental factors is not going to effect the root cause and hence can’t predictably effect factors selected by that cause, ie what is found to be sexually attractive. Therefore we can’t infer genetic or environmental control.

Two ideas in this thread I’d like to comment on:

First, it is pretty much universally accepted now that evolution takes place via punctuated equilibria.

Second, given modern medical care, etc., it doesn’t seem likely that humans are gonna evolve any more. We’re removing all the pressure. :wally (don’t know what else we could ethically do, but still …)

Now there’s a topic for debate Tygerbryght!
I don’t know how you can suggest that modern medicine is going to prevent humans evolving any more. Even if we could cure all defects completely using medicine, the stronger, richer, more attractive people are still going to be able to command the better mates. This is all the selective pressure evolution needs to continue full pelt.
Added to this medical resources are not distributed anywhere near equally. Given this medical science is probably speeding up human evolution, since the strongest, smartest and most attractive not only survive and breed, they make more money and are able to become even fitter, stronger and more attractive, and so are able to make more moeny and so on. A trait that would have had only a slight advantage 50 years ago can now be magnified 1000 fold. Consider as an example a succesful con-man genetically blessed with the gift-of-the-gab, but no oil painting. 100 years ago he sold snake oil nad made a comfortable living. Now he sells real estate, makes $10,000, gets plastic surgery, becomes more attractive and appears more trustworthy, makes more money and hires a personal trainer with a steroid supply, becomes bigger and stronger, is even more attractive and able to care for himself and selects the best mate around, or simply becomes incredibly promiscuous and produces numerous illegitimate children. Without the initial genetic advantage all would have been lost. Now the genetic advantage is multiplied.
No, you can’t stop evolution until you remove absolutely all interspecific and intraspecific competition. You can only do the former by lobotomising people, completely controlling all emotions and reactions and breeding people from randomly selected sperm/ova deposited in a central vault. You can only achieve the latter by compleetly eliminating all organisms that in any way negatively impact on human health or happiness, and that basically means sterilising the entire planet.

I was sure I’d posted a response to Gaspode, but I don’t see it…

What does it matter how much you spend to make yourself more attractive, if you have one child, or no children? :confused:

The people who will be represented in the gene pool of the future are those who (a) have kids, but especially (b) the most kids. Further, we got lotsa people nowadays who aren’t merely surviving some genetic disease which would have killed them off young; now they are themselves reproducing. Please don’t think I’m advocating the concepts of eugenics that were advocated from the late 19th century through the early 20th. I merely want people like Gaspode to recognize the effects of these events.

It’s overstated, and some of the concepts have been disproven, but I suggest you look for a science fiction collection that has either Kornbluth’s “Marching Morons” or his “The Little Black Bag” in it. Food for thought, as it were.

Or, you could start reading the editorials in Analog magazine.

It matters because if your attractiveness allows you to have that child to the fittest mate that child will have a higher survival probability than if you were unattractive. Therefore evolutionary forces are still at work and will be until such time as we can eliminate death completely from all humans under child-bearing age and ensure that all people have exactly the same number of children.

By saying that medical science has ended evolution you imply that all people have the same number of children, and that there are no wars, diseases, crimes, accidents or famines to ever kill off any of the human population.
Until this is so evolution will march onwards and can only be accelarated by medical interference within a capitalist system.

Whether this is a good or bad thing is irrelevenat. What direction this evolution takes, whether forwards to a glorious future populated by supermen, forwards to a world of moronic cripples or forwards to a world populated by two human species is irrelevant. It will go forwards.


I partly disagree. I do support your statement that evolutionary forces are still at work; however, evolution tends to occur most rapidly when an isolated population is subjected to severe environmental stresses (punctuated equilibria).

As things stand now, at least in our culture, almost every child survives to adulthood. Even many severely handicapped children (for example, kids with Down’s Syndrome, cystic fibrosis, various musculoskeletal abnormalities) have an excellent chance of survival. Also, since survival isn’t based entirely on physical fitness anymore, many kids that would have died in infancy have a good chance of surviving to have kids of their own.

As an example, my son has severe birth defects but he’s extremely intelligent. Modern medicine has given him the chance to actually walk (just started walking a couple of months ago at age 7- we’re so very, very proud!) but he’ll never be an athlete. In fact, he’ll probably always have at least one leg brace and crutches. Nevertheless, he’s so scarily smart that he will certainly be successful in whatever field he chooses. He also has such a great sense of humor and magnetic personality that I’m sure he’ll have a choice of mates someday. (I’m not just saying this because I’m his mom, either.) If he’d been born a hundred years ago, he’d have died in infancy, but he will almost surely live to pass on his genes.

You and your mate don’t have to be particularly fit or wealthy (in fact, you can be complete social and genetic losers) but any offspring you have will almost surely survive. Not much evolutionary pressure going on.

Wealthy people tend to have fewer children; poor people tend to have more. Still, the differences between the rich and the poor (unless you’re a firm believer in The Bell Curve) are mainly social, not genetic differences.

Furthermore, with billions of people in the world, few populations are genetically isolated now. More than ever before, human populations are mixing, sharing genes. This, combined with high survival rates, almost puts evolution at a standstill.

Now, if we were to experience a catastrophic plague or nuclear war, evolution would spring back into action.

I disagree. The nearing revolution in genetic engineering will artificially accelerate the “natural” evolutionary processes–and distort it, of course–by millions of times. Biologic/genetic changes that may have taken untold millennia to occur will be achieved almost instantly. We cannot even begin to imagine what shape these changes will take–kids with 600 IQs, superhuman strength, and 200-year lifespans???–but they are our destiny.

Holly, I’m having trouble agreeing with almost any this.

Firstly punctuated equilibrium is at best a theory, and not one that is by any means universally supported. It is applied largely to the rate of speciation in an attempt to explain fossil records and makes no assumptions about the rate of evolution, which is surprisingly constant and based mostly on generation span, not on environmental factors.
Even if it were a fact there is no way of measuring whether it works faster amongst any given population under any given circumstance. We can only imply this by what we see now and there are numerous examples of where apecies diversity is highest in highly stable zones
I suspect in addition to this that you are confusing the current theory amongst ecologists that speciation occurs most rapidly at ecotones, with the rate of evolution. Speciation is largely untied to evolutionary rate. Speciation is the rate at which new species arise, and this can result from one mutation, evolutionary rate is a general measure of the overall change in genetics in a population and many mutations can occur without creating a new species. Within freely interbreeding populations a gene can rapidly become widespread, leading to an evolution of the whole species but without creating a new species.
Yes most children in western society survive. A high survival rate amongst offspring does not in any way slow down evolution, it simply alters the survival advantages inferred by certain genes and moves pressure through generations. The only way you could stop or even particularly slow evolution would be to ensure that no individual ever died before childbirth and that every individual had the same number of offspring.
At one time many men with physical disabilities would have died. These days they will give birth to children themselves. However if a depression strikes and the only work available, even for five years, is manual labour that they are incapable of doing then they are at an economic disadvantage. If a disease then strikes that requires money to treat they will suddenly find their children at a reproductive disadvantage. Many people with genetic handicaps can give birth to children, but they cannot attract as wide a range of mates as if they did not have those handicaps. A person with asthma may no longer have a higher chance of dieing before giving birth (though we still do) but most asthmatics will find it hard to attract girls who are only attracted to track and field stars. This may sound like a trivial thing, but that inability to choose ‘any’ mate may lead to children with even more genetic handicaps, which will inturn limit there ability to choose mates and so on. Once any pressure is placed on a population such as a new disease or famine these individuals will succumb more frequently. All that keeping people alive does from an evolutionary viewpoint is push the pressure further down the line. Like any closed system so long as the pressure exists it will impede flow as soon as the flow alters. Physical fitness may no longer confer as large a survival advantage its true, but this just means that other genes are more important.
Just because your young survive doesn’t mean that all the future generations will. ‘Social and genetic losers’ will find their genes selected against in the lifetimes of their grandchildren and great grandchildren if not today. The first new epidemic like Spanish ‘flu, the first social upheaval like a depression or revolution, the first environmental glitch like a drought or earthquake and suddenly the genetic choices of the last hundred generations suddenly become just as important as ever. Until we can eliminate wars, earthquakes and disease then we will not slow evolution even one iota. All we do is create bottlenecks. Even in the absence of any external stimulus there will still be evolutionary pressure between sperm that will derive the process in one direction or the other.
The degree of mixing of populations is largely irrelevant form an evolutionary standpoint. If a gene confers an advantage it will survive, if not it will die out. The gene doesn’t care whether it survives in a black man or a white man. I should add to this that if you put the user name ‘Collounsbury’ and the word ‘race’ into the SDMB search function you will find several threads proving that there is no evidence that human populations were ever genetically isolated and considerable evidence for constant genetic mixing throughout human history.
Evolution continues apace in humans so long as we remain mortals with free will over family size.


This makes sense to me. In places where there isn’t an unusual amount of selective pressure, people will tend to diversify. Once a plague or famine hits, though, anyone carrying less-than-ideal genes will be winnowed out.

I didn’t mean to make it sound like I thought human populations were absolutely isolated in the past, though I’d suppose certain populations were nearly isolated, for example, in Hawaii, Australia, etc… I understand that populations have always mixed, but I maintain the the rate of such mixing has increased.

Yes, but because genetic engineering is artificial, it won’t necessarily confer survival benefits. For example, we could engineer a population of healthy, strong, intelligent people. However, if a plague strikes and the non-engineered people carry a gene that helps them survive it, the engineered people might not have the advantage. If we could predict what natural or social disasters will occur and when, this scenario would be different.

Is it very important to be able to choose ‘any’ mate, or is it just necessary to be able to choose a fit mate? How large must the pool of prospective mates be? By this, I mean that in the past, it was common for people to be restricted to a relatively small pool of prospective mates. If you lived in a small farming community or tribe, you might find a dozen eligible mates. Now, many of us live in places where the pool is much larger or at least have access to more potential mates. This increases the odds of less-than-physically-perfect people to find a fit mate.

I don’t claim to be an expert on any of this, and I defer to your judgement. :slight_smile:

I believe that Gaspode was using the word constant in the sense of continuous, not in the sense of “at the same rate”.

In re reduced gene flows, Australia of course is something of a valid example, Hawaii representing a recent colonization (relatively speaking) is not. Check out some of the links in the otherwise depressing race threads.

(Parenthetically has an excellent resoruces and search function re precisely this topic, which I have made great use of in order to track down the latest literature. If you have a yen for examining this --and apologies in advance if you are already acquainted with it-- its a real gold mine. Of course my problem is the connections currently available to me suck --even though I ahhh ‘wrangled’ access to a university server for home use.)

Genetic revolution:
To Gaspode and Holly. I think that we need to examine differential access. I’m not sure even in the medium term what effects will be. Certainly in re, for example, agricultural engineering we face some important concerns in this area. (And thus my paycheck…) Ultimate results on a genetically significant timescale?

(Otherwise glad to see an informed discussion.)

It’s not people I;m referring to, its species in general. People don’t seem to fit any particular pattern. My point behind saying that genetic diversity is often highest in the most stable ecosystems is that constant and violent stress is not needed for evolution to continue full speed.
The reason you suggest is probably incorrect, since it would tend to lead to a decrease in diversity, simply because after a very small number of catastrophes all individuals in an interbreeding population would be carrying the same genes. What actually seems to occur is that with little catastrophic pressure almost all genes contribute some survival advantage. They are all favoured at some stage within an individuals life span or it’s offspring’s, so some genes are favoured in summer, some in spring, some in the rain etc, and very minor selection pressures begin driving evolutionary change. Even in tropical climes a gene that provides protection from ice for example will confer some small survival advantage occasionally and can be selected for if it doesn’t get swamped by a more vital gene for starvation mitigation.

It may well have done. Even given this however the rate of mixing will not effect evolution, only the rate of speciation. Mixing simply allows a favoured gene to spread through the whole population rather than producing a new species.

I couldn’t agree more. My point was simply that evolution is continuing apace and hasn’t been slowed by science or medicine. Whether the current direction is going to confer survival benefits to all individuals is irrelevant The direction of the evolutionary process is always completely unpredictable and many genes will be exterminated. Natural selection won’t pre-adapt all people to new catastrophes like diseases, it can only adapt them to existing stressors. That’s how the process works.

What is important is being able to choose the fittest mate. Anything less and the individual lowers the reproductive fitness of its offspring and decreases its chances of passing on its genes. Therefore any limitation in the range of mates available contributes to a lessening of survival potential. This may be trivial, but in stable environments it is these trivial advantages that drive evolutionary change.

For optimum survival of an individuals genes the pool must be as large as possible. All potential mates must be included I the pool.

There’s little doubt that almost everyone in medieval Europe married. This is probably the case in every human society. Less than perfect (whatever that means) people have always found mates. The point is that a less than perfect person will find a less than perfect mate and have a greater chance of producing less than perfect children. For example I am a mild asthmatic. No major health problems, I’m emotionally stable and functionally intelligent, I don’t require medication for the condition and don’t even have any major health issues due to being asthmatic (I’m a competitive distance runner, play a variety of sports etc). However if my ideal woman were only attracted to sprinters then I’m stuffed because of a genetic handicap. So I’d have to select the ‘next best’. Similarly the woman who bears my children, given a choice between myself, and an exact copy of myself who wasn’t asthmatic would probably be inclined to select against me. The difference from a genetic viewpoint may be small, but in a stable environment such as we have created the tiny selective pressures against me and my children will be all that will drive the process. Maybe they won’t achieve quite as well at school due to being asthmatic. This leads to them being less attractive to a mate and so on. These pressures build along the line, and when a famine hits my descendants will have less money than the descendants of my hypothetical double who didn’t have asthma. My descendants will starve first and the lack of choice in ‘prime’ mates will suddenly take its toll.