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Author Topic: Why aren't humans still evolving?  (Read 8008 times)

Michelle

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Why aren't humans still evolving?
« on: 03/08/2009 10:30:03 »
Michelle asked the Naked Scientists:
   
So why aren't there signs of human evolution still?

What do you think?


 

Offline Madidus_Scientia

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Why aren't humans still evolving?
« Reply #1 on: 03/08/2009 11:08:13 »
There is. Evolution isn't something that can stop, it's just a very slow process. You won't notice any obvious changes within your lifetime but that doesn't mean we aren't evolving.

http://discovermagazine.com/2008/jan/human-genome-reveals-signs-of-recent-evolution
Quote
New genetic evidence suggests that evolution has continued to shape our species powerfully over the past 100,000 years. By looking for signals based on how much DNA mutates over generations, researchers found clues that as much as 10 percent of the human genome may be linked to these recent adaptive genetic changes.

Cornell University population geneticist Scott Williamson and colleagues analyzed over a million genetic variations in DNA samples from 24 individuals, including African Americans, European Americans, and Chinese. They were looking for regions in the genome where a beneficial mutation is carried by everyone in a population. Then, by looking at the variability in the DNA surrounding the mutation, the team could figure out how long ago the mutation spread through the population.

More than a hundred sites in the genome showed strong evidence of recent selection, including genes that affect muscle tissue, hair, hearing, immune-system function, skin pigmentation, sense of smell, and the body’s response to heat stress.

For some of the traits, it’s easy to identify evolutionary pressures that could have favored certain mutations. Immune-function genes are logical targets for selection because, as Williamson explains, “If an individual carries a mutation that provides disease resistance, that confers a clear selective advantage.”

Changes to skin pigmentation pathways probably reflect selective pressures related to sunlight exposure that humans experienced as they spread out from humanity’s origins in Africa to other parts of the world and adapted to local environments. In other cases, such as the hair follicle genes, the forces driving our recent evolution remain a mystery.
 

Offline Chelsie

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Why aren't humans still evolving?
« Reply #2 on: 03/08/2009 11:27:41 »
Madidus_Scientia is correct but there are some examples that are obvious. One example of evolution that is really obvious to the general public (you don't have to be a geneticist to understand) is that more and more people are born with less than 4 or no wisdom teeth. Thousands of years ago we needed wisdom teeth in order to help us chew through the tough meat and plants that were available to eat. With new technology we can be more selective about what we eat and cultivate different foods which can be cooked and easily digested with little chewing. Now that wisdom teeth are basically pointless, we are evolving without them.
« Last Edit: 03/08/2009 13:10:47 by Chelsie »
 

Offline BenV

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Why aren't humans still evolving?
« Reply #3 on: 03/08/2009 12:46:31 »
Interesting... Is there a selective advantage to not having wisdom teeth, or is it just that there's no longer an advantage in having them?
 

Offline Chelsie

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Why aren't humans still evolving?
« Reply #4 on: 03/08/2009 13:04:01 »
Well there really isn't an advantage to having them because 1.) they are useless, 2.) they cause more harm than good as they often become impacted and cause infection, 3.) for most people they result in long term pain until removal.

It is thought that environmental factors are influencing the growth of wisdom teeth but we don't exactly know why. Some scientist think that it is the evolution of our jaws, which are becoming more narrow and not allowing the growth of wisdom teeth in the first place. Wisdom teeth do not actually start to develop until after birth. Therefore if our genetics determine that our jaws will be more narrow than our ancestors, the wisdom teeth will not develop. This also accounts for the impaction most people suffer if they do have them. Right now 35% of the human race does not have wisdom teeth, however we do know that this percentage will increase with every new generation.

Unfortunately for me, I was born with all 4. They became extremely impacted and I suffered a major infection. During the infection I had a really high fever and passed out in the bathroom. I hit my head on the toilet and got a bad concussion and had to be rushed to the hospital. The moral of my story: Wisdom teeth suck and thank god we're evolving without them!  ;D
« Last Edit: 03/08/2009 13:52:23 by Chelsie »
 

Offline Souffle

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Why aren't humans still evolving?
« Reply #5 on: 05/08/2009 11:39:34 »
I can't imagine we're evolving as fast as our ancient ancestors did since the forces that drove natural selection and sexual selection in them aren't nearly as strong these days - the extra fast/strong/smart/healthy people aren't really any better at surviving and producing offspring these days since it seems everyone can get a date, get medicine, and if you're too unfit to go hunt down a mammoth you can still hunt down a big mac easily enough
 

Offline LeeE

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Why aren't humans still evolving?
« Reply #6 on: 05/08/2009 12:10:02 »
Evolution is still occurring in humans, as the Mad Scientist says, but evolution is about inheritance of random mutation across successive generations, so while you may see mutation in your life time you won't see the effects of inheritance unless you live through several generations.

That said, however, advances in medical treatment have become a counter factor to natural selection and mutations that would have previously been unviable and died may now survive and even produce offspring who inherit the traits that would have previously killed off that particular line.
 

Offline Make it Lady

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Why aren't humans still evolving?
« Reply #7 on: 05/08/2009 17:06:18 »
I guess the only example I can think of is that children in Japan are getting taller than their parents. It may just be the increase in western style diets but it is a generational change. Other people may know if this is a world wide trend.

Bucked teeth in girls in Japan is seen as attractive and cute so girls with bucked teeth are more likely to get a partner. Will this make the next generation of Japanese people look like Bugs Bunny? watch this space.
 

Offline caipocha

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Why aren't humans still evolving?
« Reply #8 on: 05/08/2009 19:02:42 »
I guess the only example I can think of is that children in Japan are getting taller than their parents. It may just be the increase in western style diets but it is a generational change. Other people may know if this is a world wide trend.

I'm guessing that's far more environmental than genetic.  (It would be very impressive genetic drift!)

Lots of people are talking about natural selection, which may very well not be happening so much anymore.  But sexual selection and DNA insertions done by viruses and bacteria ( newbielink:http://news.nationalgeographic.com/news/2007/03/070305-evolution-germs.html [nonactive] ) are still happening.  I think we're going to see the human race shaped far more by sexual than natural selection in the next few generations, as with Make it Lady's example of the bucked teeth.
 

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Why aren't humans still evolving?
« Reply #8 on: 05/08/2009 19:02:42 »

 

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