To what extent have humans evolved since becoming homosapien?

[abskebabs]

Since my recent thread on a related subject, I cannot help but wonder the extent and nature to which as a species we may have "evolved", adapting to different environments and lifestyles since becoming homo-sapiens. In all honesty, I am not much better than an educated layman at biology, especially so evolutionary biology, so I was hoping I could get some input on these kinds of questions from people in the forum.

 

My understanding from my school education was that biodiversity is present in human beings, though has never been significant enough, coupled with the fact that human populations have never been isolated enough from each other to allow for sub-species to emerge. Is this assessment correct, or does it require some revision, and on what grounds?

 

Also, is it reasonable to suppose we have had selective pressures acting on us in the first place, especially in recent times(by that I mean the last 50000 years or so), with the development of a division of labour, trade and agrarian societies and civilizations. My view again, from my general education was that we were largely able to escape the environmental selective pressures prevalent to other organsms, hence stopping or inhibiting evolution by definition. Is such a view naive, or close to the mark?

[Ophiolite]

My view again, from my general education was that we were largely able to escape the environmental selective pressures prevalent to other organsms, hence stopping or inhibiting evolution by definition.

Do we live in an environment?

Yes.

Is this environment different from the one we used to live in?

Yes.

Will this create evolutionary pressures?

Yes.

 

Examples:

Some humans living at high altitude for many generations have evolved to handle the lower oxygen levels.

 

Some humans have evolved the capacity to continue drinking milk into adulthood.

 

Some humans with characteristics that would have been damaging/fatal in a different environment are able to survive, prosper and reproduce. This certainly alters the distribution of alleles in the population, which by definition is evolution.

[abskebabs]

Do we live in an environment?

Yes.

Is this environment different from the one we used to live in?

Yes.

Will this create evolutionary pressures?

Yes.

 

Examples:

Some humans living at high altitude for many generations have evolved to handle the lower oxygen levels.

 

Some humans have evolved the capacity to continue drinking milk into adulthood.

 

Some humans with characteristics that would have been damaging/fatal in a different environment are able to survive, prosper and reproduce. This certainly alters the distribution of alleles in the population, which by definition is evolution.

 

I see, certainly you make a clear case with the analogy provided concerning humans living at high altitude. So you're conclusion would be even now we are subject to evolutionary pressures?

 

I only have doubts because I can see certain technological and societal developments as perhaps having allowed us to escape evolution along a certain path. For instance, the invention of clothes allowing us to escape developing a kind of fur for habitation in cold climes. Additionally, recent technological developments allowing for the treatment of genetically based diseases, maintaining populations that would otherwise have not survived.

 

I see the basis of you're argument, we still live in an environment, and so in some sense it must "select" who makes it to the next generation. Would you say the development of civilization has at least "shifted the goal posts" in terms of the selective pressures applied to humans?

[Ophiolite]

So you're conclusion would be even now we are subject to evolutionary pressures?

Certainly. There is no way of avoiding it, all we can do is to modify it. (In this regard I ignore the possibility of wholesale genetic engineering.)

 

 

For instance, the invention of clothes allowing us to escape developing a kind of fur for habitation in cold climes.

Therefore mutations that lead to us being less suited to handling cold conditions will not be selected against and, if associated with a beneficial trait, could become dominant in the population.

 

There is no disputing that the development of civilisation has changed the direction(s) in which we are evolving, but it has not and cannot change the fact that we continue to do so.

[granpa]

I wonder if our ancestors had some kind of caste system? I wonder what effect such a system would have if it existed long enough

 

A quick glance at various caste systems gives:

rulers

soldiers

 

priests

scholars, teachers

 

professionals

workers, farmers, herdsmen

 

slaves, untouchables, butchers

Edited June 14, 2009 by granpa

[Mokele]

We often forget humanity's oldest and most potent enemy - disease. Over the centuries, we've adapted in the face of a never-ending swarm of pathogens, and this is dramatically evidenced by what happens when long-separate cultures interact and pass germs (as happened with the Native Americans and Europeans).

[Ophiolite]

We often forget humanity's oldest and most potent enemy - disease. Over the centuries, we've adapted in the face of a never-ending swarm of pathogens, and this is dramatically evidenced by what happens when long-separate cultures interact and pass germs (as happened with the Native Americans and Europeans).

Correct me if I am mistaken, but your example is about what the immune systems were able to deal with, based upon prior exposure, and had nothing to do with genotype.

[D H]

Correct me if I am mistaken, but your example is about what the immune systems were able to deal with, based upon prior exposure, and had nothing to do with genotype.

How about sickle-cell anemia, which genetically confers resistance to malaria, and the CCR5-Δ32 mutation, which genetically confers resistance to smallpox and HIV?

[Ophiolite]

I was not aware of the one giving smallpox resistance. However, my understanding was that the devastation of native American populations following European contact was a direct consequence of lack of exposure amongst the natives, not large scale geentic resistance on the part of the Europeans.

 

I am not disputing the occurence of mutations that afford some measure of protection against diseases, I am questioning the examples offered by Mokele.

[Mokele]

However, my understanding was that the devastation of native American populations following European contact was a direct consequence of lack of exposure amongst the natives, not large scale geentic resistance on the part of the Europeans.

 

It's both. The CCR5 deletion mutation gives full or partial resistance to some strains of HIV also gives resistance to Black Death and smallpox, and is found commonly in European populations, but almost vanishingly rarely in other groups (Link). This would mean that a hypothetical 'first contact' between cultures would involve a population of Native Americans with no resistance (acquired or inherited) with a biased sample of Europeans (those with enough inherited and/or acquired immunity to survive childhood and remain healthy enough to sail).

 

In a sense, you're correct that it's lack of exposure, but both on the individual timescale and on an evolutionary one. Without the disease, a population will acquire neither individual nor population-level resistance, while with the disease, a population can potentially show both.

[Sisyphus]

All that's needed for selection to occur is for different genes to be correlated for any reason with different average numbers of viable offspring. (And even without that, there would still be drift.) Civilization has obviously changed our environment a great deal and therefore changed the course of evolution, but it certainly hasn't stopped it.

[abskebabs]

All that's needed for selection to occur is for different genes to be correlated for any reason with different average numbers of viable offspring. (And even without that, there would still be drift.) Civilization has obviously changed our environment a great deal and therefore changed the course of evolution, but it certainly hasn't stopped it.

 

I guess over time, assuming our species lasts long enough, this may produce an interesting feedback mechanism between our societal development and our evolutionary process. What do you think?

[D H]

A google search on this topic gives this book: The 10,000 Year Explosion: How Civilization Accelerated Human Evolution by Gregory Cochran and Henry Harpending. You can read excerpts at both Amazon http://www.amazon.com/000-Year-Explosion-Civilization-Accelerated/dp/0465002218 and at Google books http://books.google.com/books?id=VrpUh0rRYvsC.

 

The authors' web site: http://the10000yearexplosion.com/

 

A blog: http://scienceblogs.com/gnxp/2009/01/the_10000_year_explosion_how_c.php

 

 

I don't know how this hypothesis is viewed amongst the evolutionary biologists and anthropologists.

[Sisyphus]

I guess over time, assuming our species lasts long enough, this may produce an interesting feedback mechanism between our societal development and our evolutionary process. What do you think?

 

I think that's inevitable, yeah. Ours seems like it would have to be an extreme example, but I think the "feedback mechanism" is universal. Every species becomes a part of its own environment, thus making the environment different from what caused it to evolve to that point in the first place, etc. We humans have obviously radically changed our own environment in a very short period of time (and everybody else's environment, too - the rise of human civilization is a global mass extinction event), and what's going to happen in the long term is anyone's guess.