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Natural Selection, why not even better?

by Gerinski
Tags: natural, selection
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Aug17-14, 08:12 AM
Ryan_m_b's Avatar
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Quote Quote by Gerinski View Post
^ I think not even that is relevant anymore for humans, now (in developed countries at least) everybody has basically the same chance of survival and reproduction, tall or short, clever or dumb, physically strong or weak. Of the relatively few people who die without any offspring, I don't think for many of them the cause was a weak genetic profile (except for those few who die very young due to some severe health issue). And it's not the case anymore either that the 'fittest' have more offspring than the average person.
In the developed world natural selection is not present anymore. Will this have any long-term effects in the quality of the human gene pool? who knows...
There is no such thing as a "weak genetic profile". Whether or not a gene is advantageous, neutral or deleterious is almost always entirely contextual. A gene granting resistance to a certain disease is of no benefit in a society with adequate hygiene and healthcare. In fact it might be a disadvantage if there are side effects to resistance (e.g. sickle cell trait and malaria).

You seem to be leaning towards a way of thinking that "fitness" in an evolutionary sense is equivalent to everyday human usage implying that with strong selective pressure we would all be strong, smart, healthy individuals. Aside from the fact that being strong, smart etc isn't always the best survival strategy when it comes to health you need to consider the evolutionary arms race between predator/prey and host/disease. Essentially whilst natural selection might lead to a species developing resistance towards a certain disease it can also lead to the disease adapting to work around said resistance. Most of the time this means that no species comes out dominant but rather there is a constant too-and-fro, this is called the red queen effect.

If you apply this to the way of thinking that using technology to keep people alive makes us weaker you realise that this isn't the case. Without technology we would have a situation in which generations adapt to fight disease but disease keeps up ensuring a constant threat.

Quote Quote by Gerinski View Post
BTW, what is the proposed explanation for the persistence of genetic disorders which affect the chances of reaching adulthood or of reproduction in the gene pool? Such as cystic fibrosis, which causes infertility (in 97% of the males and 20% of the females according to Wiki). A simplistic Darwinian interpretation would suggest that such a disorder should have long been eliminated from the human gene pool but the fact is that it is still relatively common in Caucasians. This is another form of the question "why not even better?". Why not having eliminated such genetic disorders altogether?
Cystic fibrosis is caused by a recessive mutation. You can carry a copy of a damaged CFTR gene and be absolutely normal if your second copy works fine. You can only have cystic fibrosis if both your parents are carriers and through chance (a 1/4 chance) passed on two faulty copies to you. Thus whilst a person with CF is unlikely to reproduce due to infertility and reduced life expectancy genes leading to CF persist in the population due to carriers.
Aug19-14, 02:57 PM
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Why haven't any animals evolved wheels? Surely that would be an improvement for speed.
Aug19-14, 03:57 PM
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Quote Quote by Jupiter60 View Post
Why haven't any animals evolved wheels? Surely that would be an improvement for speed.
Aug19-14, 04:21 PM
Drakkith's Avatar
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Quote Quote by Jupiter60 View Post
Why haven't any animals evolved wheels? Surely that would be an improvement for speed.
There's only one case in which they have, but that's restricted to certain types of flagellum used by bacteria.

In large, multicellular amimals there is no evolutionary path from legs to wheels that isn't fatal or nearly fatal to an animal. The intermediate steps between legs/arms and wheels are effectively useless for anything else. In addition, a wheel and axle is a very specific configuration that is much more complicated than other types of joints. A free spinning biological joint is practically impossible. The species would need to evolve totally unique ways of supplying oxygen and nutrients to the tissues of the wheel without using blood vessels, and it would need to evolve this mechanism before evolving the wheel.

Put simply, the adaptions necessary for wheeled locomotion are extremely unlikely to evolve via natural selection.

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From the link above:

The fact that only very small creatures have evolved the wheel suggests what may be the most plausible reason why larger creatures have not. Itís a rather mundane, practical reason, but it is nonetheless important. A large creature would need large wheels which, unlike manmade wheels, would have to grow in situ rather than being separately fashioned out of dead materials and then mounted. For a large, living organ, growth in situ demands blood or something equivalent. The problem of supplying a freely rotating organ with blood vessels (not to mention nerves) that donít tie themselves in knots is too vivid to need spelling out!

Human engineers might suggest running concentric ducts to carry blood through the middle of the axle into the middle of the wheel. But what would the evolutionary intermediates have looked like? Evolutionary improvement is like climbing a mountain (ďMount ImprobableĒ). You canít jump from the bottom of a cliff to the top in a single leap. Sudden, precipitous change is an option for engineers, but in wild nature the summit of Mount Improbable can be reached only if a gradual ramp upwards from a given starting point can be found. The wheel may be one of those cases where the engineering solution can be seen in plain view, yet be unattainable in evolution because its lies the other side of a deep valley, cutting unbridgeably across the massif of Mount Improbable.
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