human evolution: when male and female fully developed into separate and distinct ...?

nismaratwork

13 sexes, that must be one fun orgy, but the cleanup! Yuck. :)

pgardn

Biology is a very messy science. Thats why most people who like a tidy world choose Physics:)

cesiumfrog

You mean, several (discrete) types of individual, which can pair (binary coupling) and exchange genetic material readily (or at least far more readily than with individuals not classed as types of this species)? Not that several individuals, one from every type, all combine (each contributing less than half their individual genome) in the process of creating a complete offspring?

pgardn

I have not been at this for a while. But the rules for exchanging genetic material was quite complex and not at all worked out. At the time I looked at it they had assigned the protists mating types. The rules of which type exchanges with which type and how exchange was taking place was still being explored. They may have figured out more about this. Molecular genetics and such is absolutley exploding. Its mind boggling compared to what I learned. Im sure its somewhere out there in all its glory now explained in more detail. I just dont want to make my head hurt trying to understand it. So if you want to explain further about mating types v. true sexes (however that is defined now) be my guest.

The major point I was trying to bring is that sexual reproduction has advantages and disadvantages from an evolutionary point of view. So sexual reproduction, just like any other mechanism that is under selective pressure, has arisen independently more than once. And in some species sexual reproduction has "dissappeared". We tend to look at the world from our point of view, boy meets girl, and its just so much richer than this. I remember reading a Steven J. Gould article about the life of the male in a species of deep sea Angler Fish and feeling completely humbled, being a male myself. My wife has continued the humbling process...

nismaratwork

That is a very keen observation, and one I am not prepared to refute. I myself, enjoy a wide variety of worlds to play in.

SHAMSAEL

The sex differentiation of animals goes farther down the evolutionary line than you might have imagined.

On a related note, there was an article here on physorg a few months back about a breed of flower in north america, i think, that is in the process of evolving into a two-sex reproductive pattern, that is the mutation occurred at some point in the past but across the entire population, many of these flowers are still asexual. It was, supposedly, proof that not all animals inheretid sex from the same ancestor but that it could've arisen at different times among different species.

I would still agree, though, that our line acquired sex long before we crawled out of the sea.

nismaratwork

Given how useful sexual reproduction seems to be, I find the possibility of parallel evolution of that trait believable. Not proven, but not absurd either. Asexual reproduction may well leave a species open to extinction, but a little mutation that nudges the species from asexual to some kind genetic swap-meet could save it. It makes sense that if this is the case, we find ourselves with the survivors, and asexual organisms will have to evolve or die as changes occur in their environment, and now at a high rate with the aid of humans.

jackson6612

Thank you very much, everybody. I will need some time to assimilate the information, and make some sense out of it because I'm not a biology student - just a stupid lazy person! Shamsael, thanks for better version of the sentence.

Mkorr

This is probably a horribly unfair accusation, but the whole issues sounds like the young earth creationists Ray Comfort and Kirk Cameron's canard that the first human male did not have a female to mate with, so therefore, evolution is false. This absurdity can be read on his "raycomfortfood" blogspot blog in the articles "the atheist and first dog" and "Evolution's explanation for male and female". I won't link to them, because the blog posts are, in my opinion, horribly cranky.

nismaratwork

Huh? Who are you accusing, and where do you get the notion that any of this is anything but support for evolutionary theory? I'm completely baffled here.

jackson6612

Is Mkorr accusing me of being a young creationist?

mheslep

I would have said plants invented preproduction through sexual separation? What ever the original source, I believe the evolutionary motivation is that spreading genes around between organisms of the same species provides an evolutionary advantage over asexual reproduction.

pgardn

Assuming that sexual reproduction produces more genetic variation when necessary (whatever conditions might warrant the need). But asexual reproduction could also claim to be much a much more efficient way of reproducing. There appear to be advantages and disadvantages for both. Both mechanisms are still around. So it is interesting to study populations of organisms that go back and forth between both I should think.

jackson6612

Hi PG

Would you please tell me which animals/organisms reproduce asexually? I have always thought that animals reproduce sexually - copulation. Plants reproduce asexually because they have no other way. Pardon me for my ignorance, if there is something utterly wrong with what I have said. Please keep your reply simple, I'm not a biology or science student.

Thanks
Jack

Pythagorean

I'm glad someone mentioned plants. Perhaps sexual differentation was something coded by a common ancestor between us and plants?

(not a biologist)

arildno

I have to reiterate that I personally think that sex differentiation (leading to our own) must be somewhere in the early history of mammals, rather than even further back (say, to plants).

Why?

Answer:
Nipples.

That already sex differentiated males should develop nipples that serve no function, is meaningless.

Thus, we are left with two alternatives:

A) Sex differentiation in mammals correlated with a reduction of capacity for lactation in the emergent males, and, probably, an enhanced capacity for lactation in the emergent females.

B) Nipples arose from an entirely different reason than lactation, and sex differentiation had already taken place. The already differentiated sexes then developed their nipples into different functions, crossing the line from non-mammalians to mammalians in the process.


As for now, I haven't heard any good argument for advocating B)-type histories.



It follows from my tentative adherence to A)-stories that I think sex differentiation is a fairly easy trait to evolve, and that has done so a number of times independently.
Perhaps I an totally wrong on this.

pgardn

Animals cover a wide range of organisms that you might not consider animals. For example there are numerous sponges, jellyfish, worms that can reproduce asexually. Copulation actually means male "parts" enter female "parts". There are many animals in which this does not happen. To copulate you have to "find" a partner. Another more random way would be just laying eggs and having males "spray" sperm rather randomly. Many fish do this... as there is a medium to help cell meet cell (fertilization) and that medium is water. Land animals are more likely to copulate as the medium for transport of sex cells might just be air (I think you can see problems with male animals just spraying sperm randomly into the air; the Catholic Church does anyway...). Plants of course have no problem with air as a transport medium. But to make it more efficient one group of plants, the flowering plants, often enlist the help of insects. So we have the birds (copulate) and the bees statement. Bees really are the transport medium for many plants to have sexual reproduction.
Hope this kinda makes sense.