Is Modern Evolution Hampered by Rapidly Changing Selection Pressures?

[DaveC426913]

The general consensus I think is that evolution is still occurring in modern times but just being driven by different factors than geography, climate, predation, etc.

But doesn't the process require time as well?

Flora and fauna (including humans) evolve characteristics because of multi-generational reinforcement selectively preferring that trait, cauing it to increase in frequency in the population.

But if the selection drivers change with every generation, or even many times per generation then how does the process result in any long-term accumulation of changes?


For example: we might have evolved an upright posture as we moved from forest to savanna. This would have been reinforced over many, many generations because the same drivers are in place over all those generations.

But in the modern world (and not just the human world) things are changing so fast that the next generation might be facing a whole new set of challenges. As a dumb example, a generation ago, success (and thus breeding) might be facilitated by a head for number-crunching, but now calculators render mental number-crunching a non-advantage, so our
children will choose mates differently.

Even though selection is occurring, it's not occurring over time, so there's no consistency. It's kind of like a heart in fibrillation - it's still beating, it's just pulling in every direction at once, and so gets nowhere.

 

[mgb_phys]

The general consensus I think is that evolution is still occurring in modern times but just being driven by different factors than geography, climate, predation, etc.

Whats different?

Flora and fauna (including humans) evolve characteristics because of multi-generational reinforcement selectively preferring that trait, cauing it to increase in frequency in the population.

But if the selection drivers change with every generation, or even many times per generation then how does the process result in any long-term accumulation of changes?

If the drivers are too steep and change too quickly the species dies out - tough.
Otherwise - evolution doesn't just drive a single change like textbooks examples of a giraffes neck, it is runnign multiple changes in parallel - some of them might win.

Rapidly changing enviroments are good for evolution.
If you have a stable environment you get slow change, your coat might be 0.1% thicker than great-grandads but the advantages is so small that it gets swamped by accidents
But if there is an ice age coming and your 0.1% better coat makes you 1% more likely to live then it suddenly has much larger selection pressure. The punctuated equilibrium school of evolution believe that rapidly changing circumstances are the only time evolution really makes any headway.

 

[DaveC426913]

Whats different?

Well,for example, we are no longer geographically isolated. Climates are changing on scales of decades rather than centuries (for example, forests being turned into grasslands).

If the drivers are too steep and change too quickly the species dies out - tough.

Yes but these changes aren't necessarily driving them to extinction, simply causing them to have different mating (or lethality) criteria for each generation.

Otherwise - evolution doesn't just drive a single change like textbooks examples of a giraffes neck, it is runnign multiple changes in parallel - some of them might win.

Yes. This much I concur. Hundreds of changes can all occur independent of each other. But I don't think that addresses the issue, since those hundreds of changes have still been driven throughout multiple generations of reinforcement.

Rapidly changing enviroments are good for evolution.
If you have a stable environment you get slow change, your coat might be 0.1% thicker than great-grandads but the advantages is so small that it gets swamped by accidents
But if there is an ice age coming and your 0.1% better coat makes you 1% more likely to live then it suddenly has much larger selection pressure.

Right, but if the ice age has gone by the time your kin mature, then that trait is no advantage anymore. Thicker coats will not be bred in.

The punctuated equilibrium school of evolution believe that rapidly changing circumstances are the only time evolution really makes any headway.

Yeah, I agree with punctuated equilibrium theory. But, like with the heart, if you speed it up too much, it seems it would stop working at all. As the frequency of changes appoaches the generational rate, inheritability would seem to become useless.

How can a particular change gain a foothold in population frequency if the very next generation does not have that change as a selection criteria?


...


Well, I guess intelligence (i.e. the ability to adapt to rapidly changing circumstances) would certainly be strongly selected for...

Hm. Yeah, I guess that's what punctuated equilibrium is all about isn't it? That in time of great change, it's the generalists who have the best odds and the specialists who die off.

So, we are evolving, but we're evolving traits that make us highly resourceful (such as brains), rather than special (such as long necks).

 

[mgb_phys]

So, we are evolving, but we're evolving traits that make us highly resourceful (such as brains), rather than special (such as long necks).

No we are evolving to be immune to contraceptive pills.
Remember we don't evolve to be BETTER, our genes evolve to make more copies of that gene.

 

[DaveC426913]

No we are evolving to be immune to contraceptive pills.
Remember we don't evolve to be BETTER, our genes evolve to make more copies of that gene.

Well then I guess we're also evolving to be Pro-Lifers...

 

[DaveC426913]

just stumbled acorss this on Digg:

Evolution stops here: Future Man will look the same, says scientist
http://www.dailymail.co.uk/sciencet...ion-stops-Future-Man-look-says-scientist.html

 

[Monique]

"But in a modern world of central heating and plenty of food, the same mutation is far less likely to give a child any advantage."

First of all, the article assumes a world where everyone has plenty of food and where all ethnic classes have mixed. We are far from that state, so there is still a lot of room for change. Second of all, he does not speak of deleterious mutations. How about the disadvantageous mutations that are not selected out? (for example blind people that can see again and deaf people that can hear again with modern technologies)

I also think that the world is a place big enough to allow for genetic drift. Humans tend to form tight social groups, even with the onset of globalization, I don't think we will abandon this soon.

"Professor Jones argues that mutation is also slowing down because of a drop in the number of older fathers, whose sperm deteriorates and contains more genetic 'mistakes'."

How about females? There is an increase in the age at which women decide to have children, strongly associated with that is the increase of genetic defects.

 

[DaveC426913]

I also think that the world is a place big enough to allow for genetic drift. Humans tend to form tight social groups, even with the onset of globalization, I don't think we will abandon this soon.

But it would require strong separation over many, many, many generations. Unlikely.

And how would people react as they became aware of these drifts? I doubt any enclave would be willing to forego the benefits enjoyed by other enclaves.

"Professor Jones argues that mutation is also slowing down because of a drop in the number of older fathers, whose sperm deteriorates and contains more genetic 'mistakes'."

How about females? There is an increase in the age at which women decide to have children, strongly associated with that is the increase of genetic defects.

I wonder why he says older fathers are on the decline ? Far as I'm aware (my wife is in the fertility industry) both men and women parents are aging.

 

[mgb_phys]

I wonder why he says older fathers are on the decline ? Far as I'm aware (my wife is in the fertility industry) both men and women parents are aging.

In western countries, older parents are richer, richer people have fewer children.
A few people waiting until they make partner before having 1 or 2 kids doesn't have a lot of effect on the population.

 

[Dale]

From an evolutionary standpoint one of the most valuable traits a modern species can have is to be tasty to humans.

 

[jim mcnamara]

In western countries, older parents are richer, richer people have fewer children.
A few people waiting until they make partner before having 1 or 2 kids doesn't have a lot of effect on the population.

Fecundity - females are in charge of human generation time. The longer the generation time the slower the popluation growth rate becomes.

For example, China could have had the 'one child' policy be something like 'have two kids anytime when Mom is past age 28' and the net effect on population growth would have been nearly the same as having one child at age 17. Of course it would have been hard to enforce. It's easier to count to one in any event.

 

[Moonbear]

I also think that the world is a place big enough to allow for genetic drift. Humans tend to form tight social groups, even with the onset of globalization, I don't think we will abandon this soon.
...

How about females? There is an increase in the age at which women decide to have children, strongly associated with that is the increase of genetic defects.

I attended a symposium last week on epigenetics, and was intrigued to find they are not just temporary effects that last only a generation or two, but once they have happened over a few generations (I think it was 4 generations of fruit flies in the one study), they somehow stabilize and result in long-term phenotypic changes. The mechanism by which they stabilize wasn't discussed in the symposium, and I don't know if anything is known about that. But, even if you remove the environmental factors that were altering methylation of a gene, after a few generations, that would persist.