Replies to This Discussion

Permalink Reply by kelltrill on February 17, 2011 at 3:27am

Jerry Coyne weighs in on this question as well.

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Permalink Reply by Radu Andreiu on February 17, 2011 at 4:00am

Evolution isn't the most accurate way to describe what happens after natural selection. Better said, it is adaptation to the environment, because evolution implies some objective measuring stick that says if we are better or not.

The real situation is that our environment is changing extremely rapidly, but it changes as we want it to change and that's in the direction of making our lives easier. That's why it may seem we're not evolving in certain areas, but we are adapting. Let's take health for example! It's much worse now in certain aspects, because of our advanced medical system and our easy way of life. While 10,000 years ago you couldn't have survived if you were obese, nowadays most people are overweight or even obese (in rich countries). That's adaptation right there, even if it may seem like involution. That's because natural selection means those who are poorly adapted die, but now we have societies that take care of their sick, handicapped and elders. That means we have softened the otherwise harsh reality of having to fight for survival.

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Permalink Reply by Dale Headley on February 17, 2011 at 4:01pm

The key factor in whether evolution, or at least natural selection for adaptive traits, is taking place in humans is to what extent changing environments are impacting the ability to reach reproductive age. Viewed in this light, it would seem that no significant evolution is taking place, at least in advanced societies, since almost all people in modern countries manage, with the assistance of modern medicine, to survive to that age. If natural selection was proceeding unimpeded, we would have long ago been rid of the many horrible genetic disorders, such as muscular dystrophy and cystic fibrosis. However, medical advances have managed to allow enough of these people to reach reproductive age that the genes get passed on. To my way of thinking, that is tantamount to putting a brake on any meaningful human evolution.

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Permalink Reply by Kris Feenstra on February 17, 2011 at 5:50pm

It's not just a question of reaching reproductive age; reproduction has to actually occur.  Poor fertility and infertility are factors.  Inability to attract a mate or unwillingness to mate are factors.

 

Admittedly, my biology is pretty rusty, but I don't think we can assume that certain genetic disorders would disappear without medical, or technological interference.  Age of onset, and the means of inheritance have to be taken into account.  With muscular dystrophy, there are numerous different types.  In some types, onset is typically around twenty-years old or later, meaning the carrier of the disorder is well into their biological reproductive years.

 

Even where that's not the case, inheritance is a factor.  If the trait is autosomal recessive, then only the homozygous recessive will be actively selected against.  If heterozygous individuals are unaffected, they will continue to carry and pass on the trait.  That said, I don't actually know the impact of disadvantageous homozygous recessive genotypes have on allele frequencies.  Heterozygous genotypes would always produce heterozygous genotypes in a 1:2 ratio in a Punnett square.

 

Ah... I'm drifting.  I have no idea where I was going with this post, so I'm putting it to a coin toss if I should just 'add reply' anyway, or ditch it altogether.

 

Tails wins it.

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Permalink Reply by Reg The Fronkey Farmer on March 3, 2011 at 8:32pm

http://www.thinkatheist.com/profiles/blogs/broaden-our-horizons?xg_...

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