|PZs title pic I got from here|
What I wanted to touch on briefly was the discussion of sex, as in sexual reproduction. Sexual reproduction is a great way to generate genotypic diversity, half your DNA comes from mom and the other half comes from dad (or the mailman). So you are truly unique, there is no one on earth with the same genomic sequence as you (unless you are an identical twin, then there is one other). So that's great right? If you have an ok genetic repertoire, by sexually reproducing with someone else, you may be able to improve the genetic repertoire of your children. If you reproduced asexually, your children are as mediocre as you are. So now that you know the advantage of sexual reproduction, what's the problem?
The problem comes from the fact that you may have a kick-ass genetic repertoire and all sexual reproduction does is mix your awesome genes with some half-breeds genes, which moves your children back to mediocrity. If you're doing well in the environment you find yourself in, chances are your children won't be doing better if they get a mixed bag of genes. If you are dealt a flush, then you are not throwing cards away to try for the royal flush (in your children). You might get shit lucky, throw away the 5 of clubs and draw the 10 of clubs completing the royal flush, but mostly you'll draw a crap card and lose out to a pair of 3s.
The Red Queen Hypothesis, which comes from Lewis Carrol's Through the Looking Glass.
"...the Red Queen begins to run, faster and faster. Alice runs after the Red Queen, but is further perplexed to find that neither one seems to be moving. When they stop running, they are in exactly the same place. Alice remarks on this, to which the Red Queen responds: "Now, here, you see, it takes all the running you can do to keep in the same place"."
The idea being that environments change so rapidly that we must continually generate diversity to survive. The argument is often presented, as in Matt Ridley's book, from the perspective of hosts and parasites. Parasites grow rapidly and have hundreds to millions of generations in the time it takes a human to undergo one generation. So our children need to be different from us because our parasites may have learned how to beat us, but will not be ready to kill our (genetically) distinct children. This makes a great deal of intuitive sense and there is data to support this idea.
I think the red queen hypothesis may explain why we, and many other organisms, reproduce sexually now. However, it does not answer the question, why sexual reproduction evolved in the first place nor why it occurs in many eukaryotes today.
|From Scientific American|
What I find fascinating is that many fungi can take it or leave it. By that I mean some species that reproduce sexually have closely related sister species that do not. Take Saccharomyces cerevisiae (baker's yeast), it's can reproduce sexually. However, a related fungus Candida glabrata (a human commensal/opportunistic pathogen) does not appear to have sex.
Another fungal commensal/opportunistic pathogen of people, Candida albicans, also seems to lack sex. However, C. albicans retains many of the genes necessary for sex in fungi like S. cerevisiae and you can get C. albicans to do sex-like things in the laboratory. Regardless, if C. albicans has sex in nature, it's not often, not for several 10s of thousands of years anyway.
If we look across the eukarya and focus on those eukaryotic organisms that cause disease in people (which most eukaryotic microbiology research has focused on anyway), then we find many, dare I say most, are asexual. If sex is awesome for us to deal with parasites, wouldn't it be awesome for the parasites to deal with us? Regardless, I do find the idea of parasite warfare a great paradigm to explain sex today, but that really explains why sex is maintained in organisms like us, not why it evolved or is maintained in other eukaryotes.
When sex evolved, multi-cellular highly complex decade-long generational organisms didn't exist, so what was the selective advantage for sex? or was sex simply something that happened in an early eukaryotic lineage and was maintained fortuitously? Were environments more dynamic when sex evolved? If so why didn't sex evolve in the world-wide powerhouses, the bacteria?
We reproduce sexually as do most animals, a couple of lizard species excluded, therefore the biology of sex and sexual reproduction is of interest to us. But let's not assume that because something is important to us (like sex), that nature gives a damn.