Is Human Evolution Limited by Physical Constraints?

[Another God]

I've got myself into a debate about whether Evolution is currently occurring in Humans.

So far, with my initial thoughts on the subject, no matter how I approach the topic, I can only formulate Affirmative arguments. Can anyone think of any sort of case that can be built against the stance that humans are currently evolving just like everything else?

(Even if you need to 'select' your definitions, choose your versions of evolution, your types of selection or whatever...)
https://www.physicsforums.com/insights/what-is-evolution-a-beginners-guide/

 

[LURCH]

That is a tuff one. The best I can come up with is that the human race has reached a point where we are able to alter our environment to suit ourselves, rather than altering ourselves to suit our environment. You could try saying that once we began builing homes, furniture, machines etc. to fit us perfectly the way we are, pressure to eveolve ceased because any alteration from our current configuration would be a dissadvantage.

It makes sense if you don't look at it too closely.

 

[Phobos]

Originally posted by LURCH
It makes sense if you don't look at it too closely.

Agree. When you do examine it closely, it falls apart.

A.G. - I think one would need to seriously redefine/limit the terms of evolution in order to say it's no longer happening.

 

[iansmith]

I think evolution is still taking place but the enviromental pressure has change, mostly, in developed country. We still face disease and microbial attack. For example, some people are showing resistance to AIDS. If this resistance has a genetic basis then AIDS resistance migth be a new starting point for evolution.

Another theoritical example is that people are becoming excessevly obese. There migth be biological and social pressure for obsese people to be selected against. Therefore people with faster metabolism migth become the fitter individual. People with faster metabolism migth have a better overall health and migth be more fertile.

With human, social pressure and technology have an equal voice with mother nature when it comes to evolution wheres with animals technology (a wood stick to get ants is technology for a chimp) and social pressure have less influence.

Evolution also migth take a long time therefore we migth not see the results.

[Edit: spelling]

 

[Another God]

Originally posted by Phobos
Agree. When you do examine it closely, it falls apart.

Thats exactly the problem. I keep trying to think up angles on which a negative side can argue this...but every superficially convincing argument is crap upon inspection. And for this debate so far we ahve only decided which topic we want to do, and the teams haven't been sorted yet, so I don't know whether I will get to be on the affirmative or the negative...I'll just have to fight my way over to the affirmative and hope the other guys haven't thought about it yet, and so don't realize just how impossible the negative is to argue.

Perhaps I could argue that very very soon we will be able to engineer ourselves, and it is at this point that evolution will stop. We will deny the natural world control over our genes etc and start controlling the movement of all genes. Thus halting genetic drift and with it 'Evolution'.

 

[selfAdjoint]

Whatever our circumstances may be in the modern world, variation in our genes keeps happening, and our environment is still selecting some who leave more descendents than others. So the mechanisms of evolution are still under way, with what ultimate result we cannot say.

Many social thinkers worry that the more prosperous people get, the fewer children thay tend to have, on the average. This means that over the long run the prosperous (sometimes characterized as "intelligent") are evolutionary losers. Their descendents will be nothinmg much compared to the descendents of the still fertile poor.

I think this is worrying too soon. We don't know what the future of the human race will be. Perhaps there will be another bottleneck and only a few individuals will be the ancestors of all the future human race. Nobody can say. But evolution is surely wending its slow way through our species as we post.

 

[megashawn]

I mean, even if we have the ability to control our enviroments, this allows for less stressfull living, which would allow for more time for education, hobbies, etc. I'd say even if we've quit physically evolving, we could probably never reach a point where we quit mentally evolving. (which, I imagine is still physical evolution)


I mean, the less we have to be out working or hunting, warring or what ever, the more time we have to do, well, whatever we want.

I'd say not only are we still evolving, but we are slowly gaining control of our own evolution.

 

[mythos]

If you think about it, the only way any species could stop evolving is either

1) they stop reproducing

or

2) each member of the species produce an equal number of surviving offspring

 

[O Great One]

or

3) they only reproduce after their own "kind"

 

[LURCH]

Originally posted by Another God
Thats exactly the problem. I keep trying to think up angles on which a negative side can argue this...but every superficially convincing argument is crap upon inspection. And for this debate so far we ahve only decided which topic we want to do, and the teams haven't been sorted yet, so I don't know whether I will get to be on the affirmative or the negative...I'll just have to fight my way over to the affirmative and hope the other guys haven't thought about it yet, and so don't realize just how impossible the negative is to argue.

Perhaps I could argue that very very soon we will be able to engineer ourselves, and it is at this point that evolution will stop. We will deny the natural world control over our genes etc and start controlling the movement of all genes. Thus halting genetic drift and with it 'Evolution'.

Perhaps you could use the difficulty of measuring evolution as a wedge. Evolutionary biologists sometimes say (said, actully; you don't hear this much nowadays) that the process of human evolution is happening so gradually that it can't be measured.

Modern science is all about the measuring. We can measure angles down to a billionth of a billionth of a degree, make measurements of time and space to such fine subtlety that we can not distinguish between the two (but we can still measure them). Yet with all this precission, we cannot measure how the race has evolved since the beginning of recorded medical history. Cross-breeding and genetic drift, sure; but no evolutionary trend. Since in science no measurement = no validation, you might get some points with that one.

(does anybody swallow that load of garbage?!)

 

[Adam]

Another God

Is evolution currently happening to humans? This is easy to answer. Take a look at your parents and grandparents. Are you an exact duplicate of any of them? I doubt it. Most likely you will find that you have certain traits of each.

I would, however, suggest that we are mostly beyond one facet of evolution, that being natural selection. The "purpose" of natural selection is to create a version of any given species which is safe from the common threats of its environment. We are safe from such. There aren't many things more dangerous than humans. Perhaps it is still in action, weeding out those who are killed by various diseaes, heart attacks, et cetera. But let's face it, there's no animals nastier than us, no condition of weather or such that really bothers us.

 

[Another God]

Originally posted by Adam
Another God
I would, however, suggest that we are mostly beyond one facet of evolution, that being natural selection.

Nah, I don't think we are beyond Natural Selection at all. Sure, we have levelled out the evolutionary terrain some, we are free to move from unlikely phenotype to unlikely phenotype without as severe a punishment as some other organisms, but there is still selection in action maintaining a whole host of necessary genes. Selection in process maintaining various character traits and removing others (people who, say, uncontrollably **** on everyone they meet probably won't have many offspring). There is sexual selection. There is a form of selection for probably the first time in natural history, where a class of humans are simply "Choosing" to not have children. This is selecting against that type of genotype.

Resistence to bacterial infections, resistence to Viruses, cancer resistance are all under the scrutiny of selection. Heart 'disease' is even under selective pressure. As these diseases quickly become the largest killers in our society, our society is weeding out the people who succumb to them and creating hosts of people who don't. It's a gradual process, but it is happening.



So yeah. Here again is my problem. I can present pretty much every argument concievable For Evolution still occurring, and just about no arguments against it...

 

[Deslaar]

When I hear the quetion "Are humans evolving?" I often take it to mean evolving in a particular direction; that particular characteristics are being selected for and others are being selected against. If this is what you mean then I think that a case could be made that we are not.

If you are instead suggesting that humans are evolving in the sense that individuals are subject to selection pressure and differential reproduction then obviously we are evolving. All life is evolving in this sense even if it's at hasn't really "evolved" for millions of years eg. the coelacanth. I would say that the principle force involved in human evolution would be stabilising selection.

 

[Chemicalsuperfreak]

Originally posted by Deslaar
When I hear the quetion "Are humans evolving?" I often take it to mean evolving in a particular direction; that particular characteristics are being selected for and others are being selected against. If this is what you mean then I think that a case could be made that we are not.

If you are instead suggesting that humans are evolving in the sense that individuals are subject to selection pressure and differential reproduction then obviously we are evolving. All life is evolving in this sense even if it's at hasn't really "evolved" for millions of years eg. the coelacanth. I would say that the principle force involved in human evolution would be stabilising selection.

I think that certain populations are evolving, that is by your suggestion of being selected against. It's not some grand morphological change, but considering how many millions of Africans are contracting HIV, most will be dead, but there's got to be at least a few with natural immunities.

But I think you've got to look at something else besides selection. Travel is so easy nowadays that there are a lot more people with different national heritages. Take my Scottish/Japanese friend for instance. There's a lot of new phenotypes out there. So genetic drift is a serious consideration.

And giving how quickly humans have ****ed up the environment, antibiotics, etc. we'll have to worry about all kinds of selection real soon. Biologically speaking.

 

[Phobos]

A.G. - The best I would expect is that human evolution has recently slowed (time of 'stasis' perhaps) due to our global coverage & transportation technologies. I.E., we don't have many significant isolated populations anymore in order to affect larger differences. But I don't expect that to be a permanent condition (and they're still be small changes in the population during that time).

 

[Phobos]

Originally posted by O Great One
or

3) they only reproduce after their own "kind"

That's still evolution (so called "microevolution"). For example, if you think a single wolf "kind" was aboard the Ark, and that kind spread across the world and developed into the gray wolves, arctic wolves, timber wolves, etc...that is still a speciation event(s) that qualifies as evolution. Actually, evolution doesn't even require speciation...just statistical changes in the frequency of alleles (expressed genes) from generation to generation. Your concern, I assume, is macroevolution (from one kind to another). But I don't want to get off on a tangent here...

 

[DrChinese]

Taking the negative side:

Obviously the forces of natural selection and random mutation are still at work. But is there any "net" evolution considering mutations which die out?

Each of us has different DNA, even identical twins do not always have 100% identical DNA (considering replication errors). So what is the precise definition of human DNA?

The issue presumably is whether a new genetic mutation common to all humans could develop. And to this, I believe the answer is NO. The population of humans is too large, and even over a very long period of time I am not sure it would be possible in humans.

 

[FZ+]

The issue presumably is whether a new genetic mutation common to all humans could develop. And to this, I believe the answer is NO. The population of humans is too large, and even over a very long period of time I am not sure it would be possible in humans.

Er... does evolution even work like that? I would think a more probable scenario is that the differing conditions (one might imagine H G Well's the Time Machines's Eloi and Whateveritsnameis) would create a greater divergence within the species, and then we get competition both in genes and overtly, and so we have one dominating and decreasing the prevalence of the other. I don't really imagine that whole populations just uniformly change.

As to the question... Gee... devil's advocate. I suppose at some time you have to define a benchmark at which something is evolving or not, and you can set us as not evolving by definition. Maybe.

 

[Another God]

Well, anyway, the debate is next week and I am on the affirmative side after all.

Turns out the affirmative isn't quite so certainly guaranteed going to win as I initially though. As long as humans can control our environment forever, and sexual selection is largely driven by cultural pressures (media etc), then the only selective pressures are purifiying pressures (ie: The pressures which make us keep what we need to stay alive/function practically), which means we won't be evolving at all.

I can't imagining us maintaining absolute control over our environment though. One day, some virus will get through and strike nearly all of us down before medicine can react. A commet will get through our defences. We will colonise other planets and it will create situations we can't control. We will run out of food. We will run out of space. The Earth will flood. Bill Gates will buy out a political region, raise an army and kill all 'Jocks', thus providing a selective pressure to be a nerd... Etc

Any number of unforseen circumstances could arise, and selection will begin once again, and our massed numbers of variety will be selected against.

 

[FZ+]

Erm... there are always some form of selective pressure. Like a selective pressure nowadays to be slim (or not). And it's always useful to be smarter... sort of.

And I really don't think we have an absolute control on our environment at all...

 

[Another God]

Originally posted by FZ+
And I really don't think we have an absolute control on our environment at all...

No we don't, but we have a large enough control (or capacity to control) which allows us to remove any selective pressure before it can have an evolutionary effect... Remember, evolution usually takes quite a long time before anything can happen...we act much quicker than that.

And 'being smarter helps'...helps what? Helps you survive? Not really, anyone can survive in our society. Helps procreate? Not really...I'd say on average stupid people have tons more children than smart people...

 

[LURCH]

Originally posted by Another God


And 'being smarter helps'...helps what? Helps you survive? Not really, anyone can survive in our society. Helps procreate? Not really...I'd say on average stupid people have tons more children than smart people...

I would agree with that last observation. However, (and this is assuming intelligence is hereditary) this should result in a larger number of "stupid people" in the next generation. The tendency of one type to procreate more prolifically results in the more of that type in future generations, causing the entire species to resemble that type. So, if the whole human race gets dumber as a result, then that is evelution. Just not of a type we like to think about ("EVILution? ).

 

[Phobos]

DrChinese - Evolution is not just mutation. Consider gene flow (changes in population demographics). Right now, there are many varieties ("races") of our species. As our intermingling increases (loss of isolated tribes, improvements to global transportation, urbanization), the traits that we currently use to distinguish a "race" will likely be merged. Statistically, the overall human gene pool will be different than that of today's. I certainly agree that, due to our large & mobile population, it would be very difficult for a new mutation to take hold everywhere. It usually takes an isolated subgroup of an overall population (Mars colony?) in order for a mutation to get a foothold.

A.G. - Overall, I can agree that human evolution may have slowed due to our technology, etc., but not stopped.

As far as brains being helpful...it was a great help getting us this far (spreading across the globe). Now it's being put to a new test...internal (intraspecies) competitions now that our ecological niche is filled. Can we get along or will we kill each other? Or perhaps it will help us reach new niches...or save us from the next comet strike.

 

[DrChinese]

Originally posted by Phobos
DrChinese - Evolution is not just mutation. Consider gene flow (changes in population demographics). Right now, there are many varieties ("races") of our species. As our intermingling increases (loss of isolated tribes, improvements to global transportation, urbanization), the traits that we currently use to distinguish a "race" will likely be merged. Statistically, the overall human gene pool will be different than that of today's. I certainly agree that, due to our large & mobile population, it would be very difficult for a new mutation to take hold everywhere. It usually takes an isolated subgroup of an overall population (Mars colony?) in order for a mutation to get a foothold.

A.G. - Overall, I can agree that human evolution may have slowed due to our technology, etc., but not stopped.

You are right of course. Additional mutation does not have to occur for the human race to change its makeup. But the question is really: what DNA defines a human (or any species)? Specifically? How can future evolution be measured? Interesting questions, at a minimum.

 

[pmb]

Originally posted by Another God
I've got myself into a debate about whether Evolution is currently occurring in Humans.

So far, with my initial thoughts on the subject, no matter how I approach the topic, I can only formulate Affirmative arguments. Can anyone think of any sort of case that can be built against the stance that humans are currently evolving just like everything else?

(Even if you need to 'select' your definitions, choose your versions of evolution, your types of selection or whatever...)

How could someone conclude otherwise?

 

[Another God]

Originally posted by pmb
How could someone conclude otherwise?

By claiming that humans have controlled their environment, so that we adapt the environment to us, and there is no selective pressures adapting us to the environment.

 

[pmb]

Originally posted by Another God
By claiming that humans have controlled their environment, so that we adapt the environment to us, and there is no selective pressures adapting us to the environment.

We don't really adapt to our environment - that's not what evolution is about. The idea is that random mutations happen. The mutations which favor the propagation of these 'mutated genes' are the ones which will dominate. So we don't adapt per se.

And mutations happen all the time - most of them are caller "cancer" since some of the mutations go crazy

Pete

 

[Phobos]

Originally posted by pmb
We don't really adapt to our environment - that's not what evolution is about. The idea is that random mutations happen. The mutations which favor the propagation of these 'mutated genes' are the ones which will dominate. So we don't adapt per se.

And mutations happen all the time - most of them are caller "cancer" since some of the mutations go crazy

I think I agree with this, but I think adaptation is still a good word to use. Natural Selection acting upon the variation within a population (resulting from mutation and other things like gene flow & recombination) is a kind of adaptation. e.g., objectively, environmental conditions like climate may preferentially select for more hair/less hair (or whatever trait) already present within a species...but subjectively (in hindsight perhaps), it seems like the population is adapting to the new climate. But I suppose your point is that the variation is the source of change, not the environment. On this matter, I would note that some variations are caused by environmental conditions, such as bacteria that start swapping genes at a faster rate or that reduce DNA-repair mechanisms in times of environmental stress.

 

[Phobos]

Originally posted by Another God
By claiming that humans have controlled their environment, so that we adapt the environment to us, and there is no selective pressures adapting us to the environment.

Maybe someday we can consider this once the words "natural disaster", "disease", etc. are no longer needed in our language. We're still up to our ears in these things (especially in third-world countries where a significant fraction, if not the majority, of the human populaton lives).

 

[selfAdjoint]

Even if there were no selective pressure in modern life (which I do not believe), there would still be evolution, through Neutral Evolution. This is just drift caused by the accumulation of variances. And mutative variances are ocurring, every individual, I have read, has several of them in their genome.

You can't decide what's adaptive and what's not from looking at a life style that's only a century or so old. Our cities, and our welfare programs, won't last forever.

 

[Another God]

Originally posted by selfAdjoint
You can't decide what's adaptive and what's not from looking at a life style that's only a century or so old. Our cities, and our welfare programs, won't last forever.

That was precisely my argument as the affirmative. Well, basically anyway, except that I didn't say that drift is evolution, I agree with Dennett's thing that Evolution is Heredity, Variation and selection, and so at the moment we are building up headps and heaps of variation, with only a little slection...but the selection will come later. We can't avoid it, it wil happen eventually. Evolution is all three of those things, and just because wee can't always see all three of them, doesn't mean we don't have evolution at those times.

So atm, we are varietising.

Later, we will be being selected, and the mass of variation will be important.

 

[selfAdjoint]

You know there is some evidence of varietilization in present day human populations. I am not talking about the phenotypic "races" because true interfertility is common between them, but many couples (I once heard the number 10%) cannot have children. Much of this has to be variation (i.e. mutation) to the point of reproductive isolation. Nobody I know studies the systematics of such cases, but it would seem to be "evolution (at least variation) in action".

And of course this happens quite randomly with respect to our perceived causes and differences. That is what you would expect. Variation has no relation whatsoever to selection. To suppose otherwise is Lamarckism.

 

[Mentat]

I just found this thread, and I must say that the challenge looks even harder at this point than it did when I first read the title (and then I thought it was very close to impossible - and only added the "very close" because I don't want to be closed-minded).

Heck, even if you could stop all of genetic recombination/variation, and could ensure that there be no selective pressure ever induced on the species (and this is already pretty well impossible), you would stil have memetic replication and cultural evolution.

 

[Phobos]

Originally posted by Mentat
you would stil have memetic replication and cultural evolution.

This is different than biological (DNA) evolution, is it not?

 

[Mentat]

Originally posted by Phobos
This is different than biological (DNA) evolution, is it not?

Yeah it is. I guess it could be excluded for the purpose of a purely biological debate.