Skip to comments.Sex: do we really need it?
Posted on 07/30/2003 8:56:08 AM PDT by I_dmc
Birds do it, bees do it, humans do it - but nobody knows why sex evolved at all, the world congress of genetics heard in Melbourne today.
"The evolution of sex has presented a paradox to evolutionary biology for over a century," said Associate Professor Sally Otto, an evolutionary biologist at the University of British Columbia in Vancouver, to delegates attending the 19th International Congress of Genetics.
"It's known there are a lot of costs to reproducing sexually. Why make sons and males, if you could just produce females that were able to reproduce by themselves? That's a division of resources into two sexes that seems unnecessary," she said.
Not only does this seem to waste resources, the whole process is prone to failure. There's the risk of not finding a mate, and the risk of getting a disease during mating. There's also a more subtle risk: if an individual reaches reproduction age and finds a mate, it is a successful genotype - a tried and true model of a species. But then that individual mixes their genotype with a mate, with no guarantee that the mixture is going to be any better.
(Excerpt) Read more at abc.net.au ...
You're pre-supposing the existence of males. But how you get males and females that can mate and produce fertile male/female offspring? Where does the mating behavior come from?
No, I'm not. The shift from parthogenis to male/female offspring is the mutation that occured. You get a tiny sense that shifts like that are possible when you see people born as hermaphrodites. Hermaphrodites obviously can't engage in partAnd because it was such a successful mutation, it became the dominant pattern for advanced life.
The article basically makes the same point later on. Sex is the most efficient means for improving a species, so its pretty inevitable that such a mutation eventually would arise and become dominant.
You call that a life?
Neither can I, especially when the many genetic/evolutionary advantages of sexual reproduction have been well known for *decades*.
I suspect this article is yet another example of a depressingly common trend: A reporter who understands too little about a scientific story to accurately present it, but doesn't let that stop them from trying to make their report more "dramatic" by playing up humdrum ongoing research as a "mystery" or a "revolution" of some sort.
In this article, it's the "mystery" of how "no one knows" why sex exists but the adventurous scientists are hot on the trail like Sherlock Holmes...
No paradox, actually.
Sexual reproduction can easily evolve in a number of ways, including the following sequence:
1. Start with single-cell organisms which reproduce by splitting, like most bacteria.
2. At some point one of the organisms stumbles upon a way to insert its DNA into other similar organisms, thus reproducing by "proxy" like a cuckoo bird which lays its eggs in other birds' nests. The evolutionary advantage to this should be obvious. And many microorganisms do this even today.
3. Eventually there's a whole host of its (direct and indirect) offspring around, all forcibly "impregnating" each other and cross-sharing DNA.
4. Since this is a valuable trait-sharing method, over time the species refines the process so that each individual is specialized at both "donating" DNA and being "receptive" to DNA from others. At this point there is true sexual reproduction taking place, even though there are no separate "males" and "females" -- all individuals are effectively hermaphrodites.
5. Later (and this can take place at either the single-cell stage, or a zillion generations later after the species has become hermaphroditic multi-celled creatures, like say earthworms), a mutant arises which has lost the ability to donate DNA, and becomes the first exclusively "female" organism in a population of hermaphrodites. No problem, it can still reproduce by receiving DNA from the hermaphrodites, even if it can't donate any DNA to others. It, and its female offspring, will still prosper and interbreed with the rest of the "male+female" population. Or perhaps a "male" arises first by losing the "receptive to DNA" structure -- same argument either way, it can still reproduce by donating DNA to others.
6. If females arise first, there's evolutionary pressure for at least some of the remaining hermaphrodites to specialize in impregnating the female form of the species. Over time they're likely to specialize so much that they become "males only". Or vice versa for the rise of a female type if males first arose in the population. Eventually hermaphroditic forms can fade away entirely, leaving nothing but "pure males" and "pure females" as the two dimorphic forms of the same species.
A long series of much smaller mutations, each of which was sustainable and/or advantageous to the organism(s) that posessed it.
|I cannot believe a person with those academic credentials could ask such a stupid question. The genetic variation and natural selection argument seemingly cuts that to ribbons.
That ought to cut both ways, though. One of the Great Mysteries, it seems to me, is why mitochondria have never developed an adaptation that attacks or interferes with arriving sperm that carry a Y chromosome.
If I'm a mitochondrium, and I'm in the egg waiting for a sperm to come along, it is in my interest to kill any Y-bearing spermatozoa. The only way my genes get any farther than one more generation of humans is if this egg I'm in gets fertilized with an 'X'.
If this adaptation had ever arisen, it would be noticable in maybe 50 or 100 generations. We would see 60-40 or even 70-30 ratios of female to male babies being born. This would be a highly successful adaptation for the mitochrondria. Can you think of any reason why this could not happen?
Ummmmm....may I be so bold as to suggest getting some sun on your time off? Any female would look good in a maid outfit, especially if she is fit enough to be in a flightsuit!
Scratch that. I don't need trial lawyers coming after me....
Aside from when we have sex in order to procreate, our sexual needs are more psychological than physical.