How did sexual reproduction evolve?

June 6, 2004 4:41 AM

How did we evolve separate genders? I assume it happened pretty early on, since most animals have a male and female, but wouldn't it have had to happen to lots of things at once for it to actually work?
posted by Orange Goblin to science & nature (7 comments total)

One important argument suggests that genders developed socially and then concepts of the sexes followed.
posted by Marquis at 8:53 AM on June 6, 2004

Well, for one, animals that can't "mix genes" (whether through gamedes or sexual reproduction) can't actually evolve, so the first animal to develop a robust method of gene-mixing reproduction would naturally dominate and spread.
posted by j.edwards at 11:02 AM on June 6, 2004

Here's an article that answers the "why"
and here's a bit of the "when"
this is probably the best "how" I could find on the web.

There are quite a few books on it - I think Dawkins' "the Selfish Gene" has a good section on it, although I haven't read it in a long time, so you might check first.

As far as I understand, the reason it didn't have to happen all at once is that the organisms in question (protoeukaryotes) could still reproduce by meiosis and sexual reproduction was just an option, but with the increase in atmospheric oxygen the pace of life increased and the organisms that reproduced sexually more often were better able to adapt and compete at the increased pace, so the older process of non-sexual selection actually evolved sexual reproduction as the best option for survival.

(Only slightly related, I just found this Fact-Index site and it's great, try it out.)

I am intrigued by the theory Marquis mentioned, but I just can't picture some of those early organisms having a lot going on "socially". I think the gender body types are determined by the chemicals from the DNA, which are determined by previous choices made by the chemicals from the DNA, which are ... etc.

Here's one of the better articles on "Fusion Sex" and gender differentiation.
posted by milovoo at 11:15 AM on June 6, 2004

sexual reproduction is very old, much older than animals, and occurs in a lot of organisms in which it's not their only reproductiove choice. some organisms will reproduce asexually when the environment is good, and sexually when there is stress; other will reproduce sexually occasionally when their local population gets high enough to make it easy, but asexually other times.

So, in a background of always being able to asexually reproduce, sexual reproduction could evolve gradually. sexual reproduction has huge benefits genetically, and the only drawback (of sexual only) is when your population density is too low, which doesn't really occur that often, especially in larger organisms that are capable of covering large distances etc.

So, that's more sexual reproduction. Genders at the beginning were probably much more basic. for example, some organisms can use a "sex pilli" to transfer dna from one cell to the other. the bacteria are the same except that one, or both have these pilli genes. but they both don't have to have them (explains how it didn't have to happen at once) anyway, you could conceivably think of the bacteria with the pilli genes as one "gender" and the one without as another "gender". Due to the way these pilli join and things more than 2 "genders" exist though. Once this split becomes a permanent condition of your genetic makeup more changes can occur and build up.
posted by rhyax at 12:13 PM on June 6, 2004

An article at talkorigins.org recapitulates what ryhax said. I found this in an extensive section devoted to rebutting creationist claims. I expect that there's more detailed discussion somewhere on the site. In any case, there's plenty of other interesting information on evolution. The criticism of creationism gets a little shrill for my taste, but if you can look past that you can spend a long time at the site.

Also, fact-index looks like someone took wikipedia and slapped some ads on it. I've seen other sites that have done it.
posted by stuart_s at 1:07 PM on June 6, 2004

Also, fact-index looks like someone took wikipedia and slapped some ads on it. I've seen other sites that have done it.

Crap, you're right, that's so lame I figured it couldn't be the case - I though they actually created that hyperlinked content. Those Jerks!
posted by milovoo at 1:12 PM on June 6, 2004

j.edwards: Evolution can and does occur without sexual reproduction, all that's necessary is mutation. Unless you're of the opinion that all those bacteria and other micro-organisms were created like that by god.
posted by fvw at 2:46 PM on June 6, 2004