The Animal World & Natural Selection

[Holly]

First of all, thank you, Gaspode and Collounsbury, for being patient with my limited education in this area that I find very interesting.

Gaspode:

. What actually seems to occur is that with little catastrophic pressure almost all genes contribute some survival advantage.

But we still all carry a heavy load of “junk” DNA, don’t we?

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.

Then again, we know that many genetic “flaws” confer advantages in other areas. Sickle cell anemia comes to mind. What about manic depression? Perhaps, in the past, people with this disorder were shunned and were unlikely to reproduce. With modern treatment, many people with manic depression are able to lead normal lives. Manic depression may confer benefits such as increased creativity, charisma, etc.

Similarly, perhaps asthma confers some genetic benefit. During a time of low environmental stress and with adequate medical treatment, most asthmatics are able to lead fairly normal lives and reproduce. Thus, more “asthma” genes are spread through the gene pool. When some future environmental stress occurs, depending on the nature of the stress, asthmatics may be weeded out- or perhaps the (hypothesized) benefits of carrying asthma genes will confer a benefit that allows such people to survive at a higher rate.

My son’s condition is poorly understood, but there is a genetic component. Nobody in either my husband’s family or my own has ever had the condition, but there seems to be a variety of genes involved. Jake’s children (if he has them) will almost certainly not inherit his physical handicaps, but they may well inherit his intelligence.

So, I hypothesize that Jake won’t necessarily be in an vastly ‘inferior’ pool of prospective mates; he’ll be in a different pool. Some women prize intelligence and wealth over physical fitness; others seek the opposite. The interesting thing about humans is that our choice of mates can be based on a variety of factors, intellect and humor being just two of them.

Of course, ideally a person would be both physically and mentally superior, but I think that superiority in one area can override or at least compensate for deficiency in another.

[Gaspode]

*Originally posted by Holly *
Gaspode:

. What actually seems to occur is that with little catastrophic pressure almost all genes contribute some survival advantage.

But we still all carry a heavy load of “junk” DNA, don’t we?

Maybe, this was discussed here : http://boards.straightdope.com/sdmb/showthread.php?threadid=60259
It’s rather irrelevant though, since genes by definition code for something, and so aren’t junk.

Then again, we know that many genetic “flaws” confer advantages in other areas. Similarly, perhaps asthma confers some genetic benefit. During a time of low environmental stress and with adequate medical treatment, most asthmatics are able to lead fairly normal lives and reproduce. Thus, more “asthma” genes are spread through the gene pool. When some future environmental stress occurs, depending on the nature of the stress, asthmatics may be weeded out- or perhaps the (hypothesized) benefits of carrying asthma genes will confer a benefit that allows such people to survive at a higher rate.

We don’t need to wait. Asthma definitely confers advantages. Something like 75% of Australian swimming gold medallists were asthmatic children, most still are asthmatic. My ability to run unlimited distances is largely attributable to asthma. Constant low-level oxygen starvation increases circulatory efficiency in a number of ways, and the inability to breathe deeply forces you to learn how to regulate breathing. Makes for good endurance athletes.
You’re quite right that there are very few purely beneficial or purely detrimental genes. Something as simple as strength demonstrates this. The more muscle you have the stronger you are, this is an obvious advantage. The more muscle you have the faster you starve to death. This is an obvious disadvantage. Still others may be linked to other traits or to the forced devlopment of other traits. The devolopment of endurance through asthma is one example. Maybe Jake will be pushed to become more studious or artistic as a result of his genetics. The thing is evolution occurs due to the interplay of a range of environmental pressures, and they don’t to be catastrophic to select against certain genes, so human evolution won’t be stopped by medicine etc, it will just be diverted.
There’s no doubt that different people select mates based on different traits, and that no genetic ‘flaw’ will stop a person finding a mate. The thing is that not being able to get the mate we desire will ultimately select against us. That’s how evolutionary competition works within species. We just select our mates based general attractiveness because this is what we have evolved to recognise as good reproductive advantage. The selection process works both ways. We both select and are selected for in the mating game. The girl that rejects me because I am asthmatic (not that anyone would probably even know, but the fact that I’m not a track star means I’m selected against on this basis) may have been the ideal mate. Not being able to have that mate, even if I have children to my second choice, means that in some small way I have accepted second best and have been selected against. Of course the more rejections an individual gets the further down the genetic totem pole one’s mates sit, and the grater the chance of their being genetically imperfect. Ultimately evolution is till at work. We just don’t realise that attractiveness is simply a subconscious gauge of genetic fitness. Even if my children do not inherit my defects they will inherit their mother’s defects, and statistically she is more likely to have defects the less attractive she is.
Superiority in some areas can certainly compensate for deficiencies in others, but in the mating game the individual who is best served is one who has the ideal combination of size, strength, fitness, intelligence, wit, charm, money etc. That way no mate is ever unattainable. He can choose any mate he wishes to based on any criteria he desires and is never selected against. While this is the case evolution will continue.
Your son won’t be in a pool of ‘inferior’ mates, there’s probably no such thing. He will almost certainly though be selected against by some girls, as are most of us non-Brad-Pitt types, just as he will undoubtedly select against some girls. This in some small way lowers our survival potential if the women selecting against us are indeed the most genetically fit mates. This isn’t a good or bad thing. It just is and allows evolution to continue. If the women selecting against him, for example those whose primary gauge of attractiveness is physical fitness, are in fact the ones who’s genes will be selected against at some future stage then his genes will actually be selected for.
Natural selection rolls on. Evolution continues. Where it takes us who knows.

[msmith537]

*Originally posted by tsunamisurfer *

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?

Well, who got laid in your school more? The captain of the football team or the quiet, nerdy kid with the straight As?

[Palm_Cove]

Matt Ridley covered this subject extremely well in his book “The Red Queen - Sex and the Evolution of Human Nature”
He has written it from the perspective of a zoologist and he provides a lot of compelling examples of human behaviour and their biologocal origins.