Tom Sawyer

As daft as the title of this post sounds, my question involves natural genetic mutation in humans.

If I remember correctly, homo sapiens evolved about 10,000 years ago as a species. Although that isn't a whole lot of time, evolutionarily speaking, are modern humans fundamentally different from the humans then or are we still pretty much the same? Also, is there any evidence that any kind of genetic drift or anything is occuring now in our species?

In lab experiments, we can make natural selection of new traits occur fairly quickly by changing environmental variables, but humans, no matter what environment they live in or how harsh it is, remain the same.

Can anyone give me some answers on this?

nogods4me

remain the same? how so? look at the varieties of skin pigmentation, hair color, eye color, height,weight,build.

Camaban

Remind me: Australian Aborigines (who got here 50k years ago) are Homo sapiens, aren't they? (just found the actual number, 200k years)

And as for genetic drift, etc, compare a pygmie with a Dutchman sometime

the Human will to survive is incredible. any change, we adapt those things around us (skins into clothing, etc) to survive.

Basically, our bodies don't need to change much, just what uses we put things to.

Quetzal

Hi peteyh: Although there are a fair number of paleontologists and anthropologists on this board that could give you a better answer, I'd like to point out that your timeline seems to be off a bit. IIRC, the earliest H. sapiens are dated to about 200,000 ya, with "modern" H. sapiens showing up around 50,000 ya (Cro Magnon).

While Cro Magnon is slightly different in morphology than it's earlier versions, they were pretty much identical to what you would see today. The further back you go, the more differences appear. The earliest H.s. had a somewhat smaller brain-to-body mass ratio than moderns, and were smaller in build than their Homo neanderthalensis neighbors.

Yeah, there are a fair number of population-specific genetic changes that can be traced to certain geographical areas - such as sickle-cell, lactose intolerance, some cold weather adaptations, etc. In fact, H.s. is pretty diverse, genetically. (More diverse than say, chimps - even taking into consideration significant lack of gene flow/isolation between different tribes). Whether you can say it's occurring now, I don't know.

That's not entirely accurate. There are genetic differences, as I noted. However, if you're talking about speciation, 1) there hasn't been enough time, and 2) we're no longer isolated enough (the "range" of H.s. is global - the widest of any species on the planet), and 3) cultural adaptation/selection in many cases is either substantially slowing or even halting the effects of natural selection on most of the species. Once we tamed fire and developed agriculture and animal husbandry, we sort of took ourselves out of the pure NS environment.

The short answer. Hopefully someone will provide more detailed response.

Peez

In order to answer the question, we need to define just what a "human" is. What are the limits to being "human"? The species Homo sapiens has been around for about 300,000 years. All the evidence shows that we are pretty much the same, though not identical. Genetic drift is undoubtedly occurring in our species right now. In a laboratory, we can expose a population to extremely strong selection. It is the selection pressure, not the environment per se, that results in evolution. The selection that is used in laboratory experiments may be thousands of times stronger than almost anything found in nature. Not only that, but the laboratory populations in question are isolated, whereas human populations in different environments are not generally isolated. Despite this, differences have evolved in different human populations (e.g. dark vs light skin). Aditionally, humans have the intelligence to adapt to environments technologically, which is much faster.

Of course, much evolution can occur with being obvious. For example, it is hard to study the evolution of blood proteins from stone fossils.

In short, there is no reason to expect that humans should be evolving rapidly, but we do have evidence that humans have evolved. Done. Bear in mind that adaptive evolution is not expected to proceed all the time. Genetic drift is (more or less), and is the basis for the "molecular clock".

Peez

MrDarwin

I would suggest that drastic evolutionary change--meaning either speciation, or the origin of something like a new genus--requires certain events that Homo sapiens hasn't encountered in the last hundred thousand years or so. Among these are:

1. near-extinction of a population due to climate change, epidemics, new predators, or rare events like asteroid impacts (i.e., producing genetic bottlenecks in populations that are geographically isolated from each other);

2. establishment of a geographically far-flung population (which amounts to about the same as #1, except that the parent population may remain stable--examples are island colonization events);

3. exploitation of a new environment or ecological niche (often hand-in-hand with #2);

4. significantly beneficial mutations.

#4 is probably the rarest event of all, but may result in the largest changes, like the origin of tetrapods from fish, birds from dinosaurs, or cetaceans from 4-footed land mammals--although even these drastic events are turning out to have occurred rather gradually, in stages documented by the fossil record. In the long term, #1-3 probably played a major role in the origins of these groups.

GeoTheo

I think humans are evolving. The population demographics are changing. The white population of Europe and the United States is declining. If it weren't for imigration the US would have negative growth. If everybody had only one kid, the human race would soon die out. As it is, people in educated industrialized nations don't have enough children to replace themselves. People in third world contries have lots of kids. There is a direct correlation with the number of children and the highest level of education of the mother. Generally educated women bare fewer kids.
At the same time medicine in the third world is getting better so there is less infant mortality.
I think other factors affect the human gene pool also. More and more people in the U.S. are sentenced to prison. I believe this has the effect of removing certian people from the gene pool.
I think this will have the effect of lowering testosterone levels in the population.
There is a correlation between violent crime and drug use and high testosterone.
I have also wondered if warfare has a genetic effect on populations. Huge numbers of males were removed from the gene pool in Europe during WWII
Natural selection is in effect in the human population. Just think about this: Do you have any direct ancestors that died before they reached adulthood?

Peez

I concur, but I hope you don't mind if I critique the following points. Such events certainly provide an opportunity for evolution by genetic drift, but depending on whether or not there are lasting environmental changes, and whether or not one accepts punctuated equilibrium, this might not be that important in terms of substantial adaptive evolution. I do not understand this one. Depending on the population genetics model, such large populations may tend to resist adaptive evolution (even without punk eek). I suppose that a large population might be more likely to produce small isolated populations, is that what you meant? I would vote this as the most important factor by far. It may be that a lack of appropriate mutations sometimes limits evolution, but this is prone to misunderstanding. I have often thought that a population that has been evolving in a more or less unchanging environment for many thousands of generations has probably had at least a few mutations that would allow evolution in just about any direction. Thus, the reason that few new beneficial mutations are observed in living populations is that if the gene was beneficial we likely already have it. Thus, we find ourselves at an evolutionary equilibrium: evolution of brain size may have stopped because a bigger brain than the one we have is a bad idea, not because the genes that might provide a bigger brain are not available. There are also constraints, factors that prevent certain paths of evolution (e.g. no mutation is going to make an elephant fly like a bird, just due to the physics of the problem). Just how important constraints are, and how many populations are in evolutionary equilibrium, is still being researched. I suspect that major evolutionary change is due to a major change in the environment, leading to different selective pressures. For example, tetrapods evolved from fish due to their occupying a drastically different habitat: land. It is not clear to me that population size would necessarily be important.

Thoughts?
Peez

Tom Sawyer

Thanks, everyone. Those answers were very informative.

I'd also like to give a general kudos to everyone on this board. I've learned more science in my past few months here than all through my school years. Keep up the good work.

Peez

I agree, though when talking about humans one tends to encounter resistance in discussing it this way. That being said, it is important to make it clear that this does not in any way support racist drivel at all (I know that you did not say anything remotely racist, GeoTheo, I just wanted to be clear). One important point to make here is that only heritable traits (characteristics with at least some genetic basis) can evolved this way. Thus, education cannot evolve, though perhaps some genetic factor which lends itself to education might (if it existed). If there is, one would first have to establish that this higher testosterone level is heritable, and that people with higher testosterone levels tend to reproduce less than others. I don't know what the figures are, but I believe that most casualties in WWII were civilian, so perhaps almost as many women died as well (plus, although the loss of life was terrible, in population biology terms it was not high given the world population: about 60 million out of about 2.3 billion, or about 2.6%). Also, many of those who died had already reproduced, but certainly the massive mortality during that period was a chance for evolution to occur in some populations. The question is: were some alleles (genes) more likely to survive than others? Even if there were such alleles, the period of high mortality was relatively short, so likely had little effect in the long term (except, perhaps, in those unfortunate groups singled out for genocide, whose gene pools may have been altered substantially).

Peez