Why Was Sexual Reproduction Selected?

[Borodog]

The vast majority of animal species reproduce sexually. As do, I believe, the vast majority of plant species.

[madnak]

Almost all multicellular organisms do (maybe even most eukaryotes?), even the ones that can reproduce asexually. I imagine that the longer generations and smaller populations have something to do with it (and by extension the relatively low rate of mutations compared to bacteria).

Skidoo, on the off chance you're serious, I actually know very little about this subject but we did cover it in class so I suppose I'll weigh in. The "narrative" is a bit too complex to relate (particularly for someone who isn't a developmental biologist), but sexual reproduction almost certainly started as a secondary mechanism. This is most visible in some algae that exist primarily in haploid form, but sexually reproduce under situations of environmental stress (chlamydomonas are the examples our teacher used). That probably gradually became a clearly differentiated simple alternation of generations, as in sea lettuce. In animals the alternation of generations presumably fell away as increased motility and other aspects of animal biology brought the "gametophyte" and "sporophyte" together into the same organism. At first the gametes were probably just released into the environment, as they still are in simpler animals. Maybe it was the move onto land that resulted in internal fertilization? And vivipary probably developed due to a relatively large investment in offspring for complex organisms.

[Skidoo]

I am being serious. You probably already know of my skepticism, but differences of opinion are good for debate, right? SMP shouldn't be an amen choir on any issue, or so I thought.

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In animals the alternation of generations presumably fell away as increased motility and other aspects of animal biology brought the "gametophyte" and "sporophyte" together into the same organism.

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So, slowly over time, a lineage of sporophytes was giving rise through meiosis to ever more autonomous gametophytes, until one day there was a "first couple" consisting of two gametophytes with no further need of intermediate sporophytes?

[madnak]

My concern is that you may be deliberately trolling, not that you may have a differing opinion.

As for this, again I'm speculating to a degree because I haven't studied the subject in-depth (and I doubt I will, because honestly I'm just not that interested in how organisms evolved, I'm more interested in how they function right now). But if you want me to speculate - I would think it was the opposite - the gametophytes became less and less developed until eventually the sporophyte was just producing gametes directly.

[Skidoo]

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As for this, again I'm speculating to a degree because I haven't studied the subject in-depth (and I doubt I will, because honestly I'm just not that interested in how organisms evolved, I'm more interested in how they function right now).

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If you don't feel like speculating, that's fine. I'm really only looking for a logically coherent sequence of events (not so much the fine details), but then that would entail some speculation, I suppose.

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I would think it was the opposite - the gametophytes became less and less developed until eventually the sporophyte was just producing gametes directly.

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That still doesn't get you a sexually differentiated adult population, or does it? I'm not sure.

[madnak]

Well, I imagine hermaphrodites came first. I'm actually not sure why different genders evolved. Maybe someone else can shed light on it. To me it seems an advantage to have both sex organs - I suppose the mechanisms just became to specialized and complex for both to exist in the body efficiently.

But again, this is all guesswork. I'm guessing hermaphrodites came first. Will someone who knows weigh in?

[Skidoo]

Maybe that's why some guys like butch broads.

[Mickey Brausch]

I can't follow too closely this sub-thread, but, if this is seriously about reproduction of life and "two-sex prevalence", please consider this:

Our world on Earth has been from the beginning, still overwhelmingly is, and probably will continue to be until the sun goes out, a world of bacteria.

Take it from there.

Mickey Brausch

[MidGe]

Rduke55,

I am going to defer any evolution questions to you because

1. you really seem to know your stuff
2. you display more patience than I ever would when it comes to explain the obvious.


Have a great festive season dude! [img]/images/graemlins/smile.gif[/img]

[Mickey Brausch]

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Sexual reproduction was a monstrous step in evolution.

[/ QUOTE ]I'll start a new thread.