Swim, Walk, Fly?

June 21, 2006 10:48 AM

Are Humans Evolving?

Not counting changes to humans based on improved diets and healthcare, are humans evolving in any permanent way? An example would be the loss of a useless body part.

Or would changes brought on by better diets be considered evolution - in the Darwinian sense of evolution?

posted by DieHipsterDie to science & nature (33 comments total)

This thread might be helpful.
posted by Penks at 10:51 AM on June 21, 2006

A body part wouldn't be lost to inutility, at least directly, but rather would be lost if it provided selective pressure against an individual that possessed it.
posted by handful of rain at 11:02 AM on June 21, 2006

Are humans still alive and reproducing and affected by both their genes and their environment? Of course. So yes, of course we're still evolving. It sounds like you could maybe do with reading up a bit about what evolution actually involves. I recommend the mighty Richard Dawkins' "The Selfish Gene" and "The Blind Watchmaker".
posted by Decani at 11:03 AM on June 21, 2006

No, because the gene pool is so large. We could be getting more genetically diverse, but not really 'evolving' because there isn't much pressure.
posted by delmoi at 11:05 AM on June 21, 2006

A highschool friend of mine does research in this area. Here is a description of his work. The most noticable points of current human evolution are biochemical. It seems like selection pressures on our anatomy are probably pretty stable.
posted by samw at 11:12 AM on June 21, 2006

The reason a lot of people have to get their wisdom teeth removed is because our jaws are getting smaller. Of course, with the orthodontists we've evolved, we've removed the selective pressure for individuals without those teeth.
posted by Capn at 11:13 AM on June 21, 2006

Evolution is dependent on some sort of stress that causes organisms with certain traits (be it cultural or genetic) to be more successful in its environment (success->more reproduction). There is most likely an imbalance of reproduction so there should be some amount of evolution, but it's hard to measure unless you have huge sampling or millions of years.
posted by Napierzaza at 11:22 AM on June 21, 2006

Also note that sexual selection is a big one for our society because death by disease/accident are so minimal (because of cures or treatments that make it livable). This means that what a women wants in a man becomes a deciding factor in many ways.
posted by Napierzaza at 11:23 AM on June 21, 2006

Yep. From talk.origins:
There is evidence that humans have evolved in the last several thousand years and continue to evolve.

* Analysis of variation in the human genome indicates that genes associated with brain size have evolved over approximately the last 37,000 years and 5800 years (Evans et al. 2005; Mekel-Bobrov et al. 2005).
* Sickle-cell resistance has evolved to be more prevalent in areas where malaria is more common.
* Lactose tolerance has evolved in conjunction with cultural changes in dairy consumption (Durham 1992).
* Some humans have recently acquired mutations which confer resistance to AIDS (Dean et al. 1996; Sullivan et al. 2001) and to heart disease (Long 1994; Weisgraber et al. 1983).
posted by tnai at 11:24 AM on June 21, 2006 [1 favorite]

There are plenty of places in the world where resistance to disease and malnutrition would make it more likely that individuals would survive and reproduce. If you want to talk about the developed world, then nearly everyone can survive and have children if they want to, but there's still competition for the most desirable mates which has got to influence the gene pool one way or another. Also, not to be too obvious, but any genetic components positively related to fertility or the desire to have children will inevitably be selected for over time.
posted by teleskiving at 11:35 AM on June 21, 2006

David Byrne, whilst quite obviously not an evolutionary scientist, has written some interesting things about this in his blog.
posted by handee at 11:37 AM on June 21, 2006

Thanks for the link to the Byrne blog. Interesting point - evolve to what? A race of superficial internet-addicted super-picky online daters, maybe.
posted by Artful Codger at 11:44 AM on June 21, 2006

No, because the gene pool is so large. We could be getting more genetically diverse, but not really 'evolving' because there isn't much pressure.
posted by delmoi at 11:05 AM PST on June 21

Please refrain from answering biology questions if this is the type of answer you are going to provide. There is still plenty of selection pressure on h. sapiens.
posted by Optimus Chyme at 12:16 PM on June 21, 2006

Oh, and "because the gene pool is so large" is a total non-sequitur.
posted by Optimus Chyme at 12:16 PM on June 21, 2006

Possibly relevant: The Marching Morons.
posted by LarryC at 12:22 PM on June 21, 2006

delmoi: No, because the gene pool is so large. We could be getting more genetically diverse, but not really 'evolving' because there isn't much pressure.

This is based on a fallacy that evolution only happens when you have some kind of event that comes along and produces a tangible change in the population. To review a basic quantitative view of evolution. You can map the frequency of most traits onto a histogram, and get something that looks like a normal curve. Mortality and fecundity vary depending on where the individual falls on that curve. Over the course of generations, that curve may or may not change in response to natural selection.

Now here is the other side of the coin. Not only can natural selection act to change the central hump of that curve over time, (making a feature bigger or smaller for example) but natural selection frequently acts to stabilize the mean. Individuals with "extreme" traits have lower fecundity than individuals with average traits. So evolution not only explains why some groups experience radical change over short periods of time, but it also explains why other groups stay relatively stable over long periods of time. Crocodilians and Coelacanths have certainly "evolved," they have found themselves in ecological niches where natural selection maintained the same body plan over millions of years.
posted by KirkJobSluder at 12:49 PM on June 21, 2006

DieHipsterDie: Or would changes brought on by better diets be considered evolution - in the Darwinian sense of evolution?

Evolution in the Darwinian sense could mean the development of a new (or elimination of an old) feature, or it could mean something as simple as the possibility that we smell differently than our early ancestors, or we have a higher tolerance for wheat products. Quite a bit of evolutionary biology is more concerned with small-scale changes than growing an extra limb.
posted by KirkJobSluder at 1:00 PM on June 21, 2006

You do realize, don't you, that the rate at which evolution results in major change is such as to make glaciers seem hyper-caffeinated by comparison? Come back in a million years and humans will definitely have changed. But the 6000 years of human history is much, much too short a time for anything but imperceptible changes to take place.
posted by Steven C. Den Beste at 1:50 PM on June 21, 2006

I don't know the answer to the question, but I think it is interesting that cultural/social success is not equated with evolutionary success. In fact, if I'm not mistaken, higher educated couples tend to have less offspring than those without as much education, in part because they tend to start later in life.

Does that mean the traits that make one sucessful in society are being selected against evolutionarily?
posted by GregW at 1:54 PM on June 21, 2006

GregW: That's true at this extremely brief moment in history. Read the previous comment - it's irrelevant. Time is very, very, very long.
posted by dmd at 2:03 PM on June 21, 2006

So, is the appendix a leftover piece of anatomy? Could it dissappear some day?
posted by DieHipsterDie at 2:45 PM on June 21, 2006

A recent evolution is blonde hair in northern Europeans. It's interesting because it seems to have come about as a combination of ecological and cultural factors. They were living in an area that required extensive hunting in order to survive, which meant that men were often killed on dangerous expeditions. This led to there being less men than women, so the men were left to choose the women they liked, the blondes. It happened over to short a time for it to be
posted by afu at 2:51 PM on June 21, 2006 [1 favorite]

higher educated couples tend to have less offspring than those without as much education, in part because they tend to start later in life. Does that mean the traits that make one sucessful in society are being selected against evolutionarily?

No, there is research that shows why this occurs and it is not contrary to evolutionary pressures. When you are poor and your life expectancy is low your best bet is to have a lot of kinds and hope for the best. When you are highly educated and living in a stable society, it is smarter to have fewer kids and focus your sizable resources on making them the best they can possibly be. That trailer trash highschool dropout mom with 8 kids is not more evolutionarily savvy than the couple working good jobs in the city with 2 kids, because their kids will have longer life expectancies and have a greater chance of being successful enough to pass along their own genes have a greater effect on society as a whole.
posted by sophist at 3:09 PM on June 21, 2006

I think most of the "evolution" that we are going to see is going to be more like genetic engineering and less like the current long long term evolution that has brought us to where we are today. Hark Humans, the singularity approaches!
posted by sophist at 3:11 PM on June 21, 2006

disease/accident are so minimal

Huh? The top three killers in America, courtesy of the CDC:

1. Heart disease
2. Cancer
3. Accidents

Disease is on the rise because population growth is causing us all to live more closely together. Think of all the superbugs coming out of China -- they're caused by the insane population densities there, which ensure that effective pathogens reproduce quickly and spread.
posted by breath at 4:06 PM on June 21, 2006

Based on my anthropological observations, in North America people are evolving massive asses.

I think it must be a sex selection thing.
posted by Meatbomb at 5:02 PM on June 21, 2006

I should have said in my comment that I agree that sexual selection has a huge effect on human evolution, maybe even a majority. I just wouldn't say that disease and accidents are negligible.
posted by breath at 5:45 PM on June 21, 2006

breath, take a moment and reread your post.

It's a good thing that those are our top three causes of death. The vast majority of people who die at a normal (old) age die of heart disease or cancer. Wouldn't you rather that be the case than have our number one killer be some species of pathogen like it has been for most of history?

You do realize that "old age" was not a possible choice of killer on that list, right? Everyone had to die of something. We're doing quite well, in spite of all of the superbugs coming out of China... which are where, exactly?
posted by dmd at 6:35 PM on June 21, 2006

Large parts of the world never lost the correllation between wealth/intelligence and fertility -- subsaharan Africa and the Muslim world, for example. Some parts of the world are regaining it -- Manhattan, for example. (Google: "third child" and "status symbol" if you must, or just try to get a spot in nursery school...)
posted by MattD at 8:18 PM on June 21, 2006

So, is the appendix a leftover piece of anatomy? Could it dissappear some day?

DieHipsterDie - as I understand it, we don't use our appendices for much, so it is 'leftover' in that sense. The only way it would disappear is if some humans had a mutation which meant they had no appendix, and if these people were more likely to reproduce than those with an appendix (this would entail more people without an appendix reaching child-producing age than those with an appendix, or the non-appendixed being more likely to produce more healthy children than the appendixed). This process, if it occurs, will take a very long time.
posted by altolinguistic at 4:05 AM on June 22, 2006

Interesting point, dmd. I guess those statistics don't really tell us how many of those deaths are due to pathogens, or were caused by genetic/behavioral effects. So I guess we can't say whether or not "disease" (meaning infection by pathogens) is the leading killer, or what. At the same time, we're ignoring the massive effect that pathogens are having on sexual selection, and reproduction itself. I wouldn't know how to look for statistics on this topic, but it seems like STDs (especially incurable ones like herpes and HIV) must cause a bunch of difficulties for the carrier to pass on his or her genes.

With respect to the original question, I guess it doesn't matter whether disease is the major cause or not. It's certainly true that heart disease and cancer are caused by a mixture of different factors, including genetic susceptibility, environmental factors, pathogens, and luck. There's always a cause. And as long as there's death, there will be evolution.

And don't fall into the trap of thinking that evolution doesn't care about people who are too old to reproduce. Even if you can't directly reproduce, you can help protect and spread your family, who carry your genes.
posted by breath at 12:41 PM on June 22, 2006

I must say that it is revealing to see how much sheer ignorance about evolution has been manifest on this thread. No wonder creationism still gets a reaction other than ribald laughter and outright derision in America. Horribly depressing.
posted by Decani at 8:36 PM on June 22, 2006

Decani: I think the main problem is that it's really, really hard to get a grasp of just how long a timescale evolution works on. It just really doesn't matter what sort of culture or behavior we happen to have right now, unless one honestly thinks that our culture (and by "our", I mean every single culture in the entire world) is now completely frozen and we'll have the exact same behavior for the next ten thousand years.
posted by dmd at 7:33 AM on June 23, 2006