The debate over WHY sex evolved

[pcvt]

Can anyone pick out the flaws in my argument?
I am reading that the exact reason why sex evolved is a highly debated topic, but my explanation seems to be 100% feasible. I have only read a little bit on this topic, so it's mostly based on my own logical thinking and could be deeply flawed.From what I've read, a large part of the debate over why sex evolved has to do with the argument over whether natural selection works at an individual level or a species level. My hypothesis is that "it depends." Sometimes group selection may take precedence, sometimes individual selection may take precedence, depending upon the environment. In an environment that is nonthreatening, selfish organisms will spread their genes a higher rate than their altruistic counterparts, over time overtaking the selfless species. On the other hand, when there is a strong need for members of a species to survive, animals that are completely selfish are less likely to be able to survive and reproduce in their environment, when their selfless counterparts are more capable of dealing with the hardships.

Now to apply this theory to the evolution of sex. Sex increases variability within the species, thus offering the ability to adapt more rapidly to a changing environment. Sex may not offer an individual a competitive advantage--in fact it may create a vast disadvantage. However, when a catastrophe hits that requires that the species evolve--such as a species threatening virus--it does not matter that the asexual creatures would be able to produce twice as many offspring--these offspring would not be able to evolve fast enough to overcome the virus. Thus, in some cases, the organisms that we will continue to exist are those that evolved sexual reproduction.

This may be a very long term process, and in several cases, sexual reproduction was obviously selected against.

 

[DanP]

Can anyone pick out the flaws in my argument?
I am reading that the exact reason why sex evolved is a highly debated topic, but my explanation seems to be 100% feasible. I have only read a little bit on this topic, so it's mostly based on my own logical thinking and could be deeply flawed.


From what I've read, a large part of the debate over why sex evolved has to do with the argument over whether natural selection works at an individual level or a species level. My hypothesis is that "it depends." Sometimes group selection may take precedence, sometimes individual selection may take precedence, depending upon the environment. In an environment that is nonthreatening, selfish organisms will spread their genes a higher rate than their altruistic counterparts, over time overtaking the selfless species. On the other hand, when there is a strong need for members of a species to survive, animals that are completely selfish are less likely to be able to survive and reproduce in their environment, when their selfless counterparts are more capable of dealing with the hardships.

Now to apply this theory to the evolution of sex. Sex increases variability within the species, thus offering the ability to adapt more rapidly to a changing environment. Sex may not offer an individual a competitive advantage--in fact it may create a vast disadvantage. However, when a catastrophe hits that requires that the species evolve--such as a species threatening virus--it does not matter that the asexual creatures would be able to produce twice as many offspring--these offspring would not be able to evolve fast enough to overcome the virus. Thus, in some cases, the organisms that we will continue to exist are those that evolved sexual reproduction.

This may be a very long term process, and in several cases, sexual reproduction was obviously selected against.

This is not really your theory, its a rather quirky presentation of the "classical" view of why sex exist (genetic recombination increases the rate of evolution of species).

The obvious problem with this theory is the fact that any individual advantage can be replicated millions of times before **any** group or species advantages can take place.

It is very hard to give any coherent answer as to why sex exists. We may have a difficulty with this for a very long time from now on. For now we can't probbaly talk scientifically about it.

What is more easily to answer to in a scientific way is the question "Why is sex maintained" by evolution.

You also seem to have some quirks in your view of cooperative behaviors and it seems to me that you identify them with "for the good of the species" and species levels selection.
Which is false.

 

[pcvt]

This is not really your theory, its a rather quirky presentation of the "classical" view of why sex exist (genetic recombination increases the rate of evolution of species).

True, should have said my understanding.

The obvious problem with this theory is the fact that any individual advantage can be replicated millions of times before **any** group or species advantages can take place.

It is very hard to give any coherent answer as to why sex exists. We may have a difficulty with this for a very long time from now on. For now we can't probbaly talk scientifically about it.

What is more easily to answer to in a scientific way is the question "Why is sex maintained" by evolution.

You also seem to have some quirks in your view of cooperative behaviors and it seems to me that you identify them with "for the good of the species" and species levels selection.
Which is false.

Hmm...
Say for example sex evolved in a select subset of organisms. They continue to exist even though they aren't quite as fit as the asexual organisms. Thus, in numbers, the group of sexual organisms is much smaller, but aren't wiped out completely. Then, a problem comes along that puts competitive pressure on all organisms that do not adapt. Statistically, the sexual population now have a competitive advantage, and will drastically increase in numbers over time.

There still remains the problem of devolving after the competitive pressure goes away. Perhaps, due to the very low chance of evolving back to an asexual organism and the chance that a new problem will arise that will once again favor sexual organisms, this rarely happens.

Is this a feasible explanation for how sex could have originated (though maybe not how it actually occurred)?

 

[DanP]

Is this a feasible explanation for how sex could have originated (though maybe not how it actually occurred)?

Actually no, it is more appropriate as theory of why sex is maintained.

And btw, individual selection can explain recombination. There is no need to believe that recombination serves the group or the species.

 

[Ken Natton]

I’m not sure you have a correct understanding of what the controversy is exactly, pcvt. As I understand it, the question mark hangs over whether group selection or kin selection is real at all. I don’t think anybody doubts that selection at the level of the individual organism is real, it is only a matter of whether or not that works in combination with higher level selection. And even if higher level selection is a genuine factor in evolution, my understanding is that it can only work to assist the propagation of a feature throughout the population. For sexual reproduction to have evolved in the first place, it must have had some selective advantage to the individual organism. Group selection, if it is real, can only explain why it has become so much the dominant form of reproduction. There is then a real difficulty coming up with a water-tight Darwinian explanation for why sex evolved in the first place – there have been some prominent and well-informed attempts at one, including by John Maynard Smith and Eors Szathmary. But the fact that such an explanation is difficult to assemble doesn’t mean that there is any particular controversy about the fact that some such explanation must exist.

And again, I don’t think that ‘selfish organisms will spread their genes at a higher rate than their altruistic counterparts’ quite grasps the issue either. It is not the case that there are some entirely selfish organisms in competition with some entirely altruistic ones for survival. Essentially all genes and all organisms want to maximise their spread. It is just that sometimes, cooperative behaviour, between genes and between organisms, is a more effective way of achieving that maximum spread than is outright selfish behaviour. The result is that there has evolved a complex mix of selfish and altruistic behaviour between genes and between organisms, to varying degrees and with differing manifestations in different species.

 

[DanP]

I’m not sure you have a correct understanding of what the controversy is exactly, pcvt.

Yes, he does. Nobody knows why sex evolved, and it's a big question in the evolutionary biology.