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Author Topic:   Why There Are Two Sexes
Blue Jay
Member (Idle past 1598 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 61 of 63 (489717)
11-29-2008 2:11 PM
Reply to: Message 60 by heygabbagabba
11-29-2008 9:53 AM


Which came First: Sex or Gonads?
Hi, heygabbagabba.

HGG writes:

Developing the needed parts for sexual reproduction would take quite a few "random mutations", none of which would have a beneficial side effect until the point where they were fully developed.

You're apparently not following what has been said.

Sexual reproduction predates the existence of what you’re calling "needed parts." In fact, it predates "parts" of any kind: microbes were the first sexual organisms. Two microbes fusing into one was likely the first instance of sexual reproduction (and also, likely the origin of diploidy).

Later instances of sexual reproduction involved two organisms that produced single-celled gametes that would fuse with other gametes to make a new, single-celled offspring. All gametes, in this case, are identical, and any reproductive organs were also identical throughout the species. In this instance, there is sexual reproduction, but there is no male or female, no egg or sperm, and no specialized reproductive organs.

From there, single mutations can easily account for the gradual specialization of gametes and reproductive parts. Again, I'm no botanist, but I have taken botany classes, and there are countless examples of plants exhibiting varying degrees of specialization between having one type of gamete and having specialized egg and sperm, and between having one type of reproductive organ and having specialized ovaries and stamens.

-----

HGG writes:

According to Natural Selection, the sexual parts that started to develop would, for many many generations, give no benefit.

I'm pretty sure Natural Selection does not say this. In fact, I'm pretty sure that it says the opposite. Sexual organs would not have persisted in a population if they were not useful.

You're seeming to not realize that the original organisms with specialized gametes would have been spawners, not copulators. Fish, frogs, plants, crustaceans, corals, sponges, mushrooms and many other things reproduce by haphazard release of gametes into the water or air. In fish and frogs, there are no penises or vaginas: they only have a cloaca, and both types of gametes are simply expelled without guidance, like poop.

Going along with the vertebrates for a moment, frogs often spawn in amplexus, wherein the male hitches onto the female and sprays his sperm onto her eggs as she lays them. Later, male reptiles developed ways to insert the sperm directly into the female's cloaca, before the eggs are laid (if you think about it, no specialization of the female parts is really necessary at this point, so your idea that opposite "sex parts" had to co-evolve is defeated). All female adaptations would likely be to protect themselves from injury when the male parts enter or to streamline the process.

You simply do not need the big jumps that you seem to think are required. You do not need an erectile penis, a seminal vesicle, a sperm duct, a vagina, a vas deferens, testicles, ovaries, fallopian tubes, etc. to have sex. These are all "luxuries" that can be added after the fact to improve upon the process that arose long before any of those parts did. Sex did not evolve to make use of formerly useless sexual organs; sexual organs evolved to improve sex.

Your objection is defeated.


-Bluejay

Darwin loves you.


This message is a reply to:
 Message 60 by heygabbagabba, posted 11-29-2008 9:53 AM heygabbagabba has not yet responded

  
heygabbagabba
Junior Member (Idle past 3886 days)
Posts: 8
Joined: 11-26-2008


Message 62 of 63 (489756)
11-29-2008 7:21 PM


First of all, I did not mean penis and vagina when I said needed parts. I was talking about whatever parts that were needed for sexual reproduction. In the frogs/fish you mention it would be the parts that make the sperm/egg. For the microbes you mentioned it would be whatever change was required to allow for the other microbe to fuse into it in order to reproduce.

I am not a professor of microbiology but I assume there was a change to the microbe that allowed it to combine with another microbe. Now apply my previous points about two microbes needing to develop these changes and all that.


Replies to this message:
 Message 63 by Blue Jay, posted 11-29-2008 10:03 PM heygabbagabba has not yet responded

  
Blue Jay
Member (Idle past 1598 days)
Posts: 2843
From: You couldn't pronounce it with your mouthparts
Joined: 02-04-2008


Message 63 of 63 (489775)
11-29-2008 10:03 PM
Reply to: Message 62 by heygabbagabba
11-29-2008 7:21 PM


Hi, heygabbagabba.

HGG writes:

First of all, I did not mean penis and vagina when I said needed parts. I was talking about whatever parts that were needed for sexual reproduction.

It doesn't matter: the principle is still the same. Specialization is a way to improve performance, not a prerequisite for functionality.

-----

HGG writes:

In the frogs/fish you mention it would be the parts that make the sperm/egg.

And, those parts would evolve in a lineage that was already making gametes prior to the emergence of those parts. A gamete is just a cell that has had its genome halved. The process that halves a genome (meiosis) is entirely endogenous (that is, the cell itself initiates and regulates the process), so there is no need for a specialized part to produce gametes. The only "part" required for gamete production, and thus, sexual reproduction, to happen, is actually a genetic mutation.

Many modern organisms have developed specialized systems, parts and cells. Some of those cells became meiosis specialists, whose entire function is to undergo meiosis (or to produce daughter cells who will undergo meiosis). And, other cells in the organism became specialists in assisting the movement, protection and production of meiotic cells. In fact, many organisms have such specialized “parts” that the “parts” can no longer function independently, and require the aid of other “parts” to complete their duties.

It’s a bit like people in the Western world today: lawyers can mop the floor with you in the courtroom, but might still get D’s on biology exams. And, taxonomists can determine evolutionary relationships between species by looking at which way the post-orbital bristles are pointing, but they can’t grow their own food. Does this mean that we need people who specialize in farming in order to produce our own food? Of course not: our ancestors could perform a wide range of functions and were widely self-sufficient, all without specializing in anything. Specialization is just a way to improve the gestalt performance of the system (or, of the organism, in the case of sexual reproduction), not a requirement for the system to perform its functions.

-----

HGG writes:

I am not a professor of microbiology but I assume there was a change to the microbe that allowed it to combine with another microbe. Now apply my previous points about two microbes needing to develop these changes and all that.

I'm not a professor of microbiology, either, but I agree with the part of your quote above that is in blue. But now, apply some of my previous comments:

Comment #1:

Bluejay, message #61, writes:

Later, male reptiles developed ways to insert the sperm directly into the female's cloaca, before the eggs are laid (if you think about it, no specialization of the female parts is really necessary at this point, so your idea that opposite "sex parts" had to co-evolve is defeated).

Basically, everybody in this scenario has a hole. Then, somebody evolves a device for sticking things into holes. Nobody else has to evolve anything at all. You don’t need two adaptations: you only need one adaptation that takes advantage of existing conditions. If the new adaptation increases performance, it will invariably outcompete those organisms that do not have this increase in performance.

This principle applies at the level of single-celled organisms, too: only one cell need evolve a mechanism (say, a chemical that allows its membrane to fuse onto another cell’s membrane, thus transforming them into a single cell). No other cell needs to have evolved anything at all in order for this mechanism to have immediate function. They just need to have not evolved a countermeasure.

If you think about it, all a sperm does is attack and penetrate an ovum, then insert its genome. The ovum really just has to sit there and wait until it is parasitized. What adaptation is required of it?

Comment #2:

Bluejay, message #59, writes:

Thus, [the first sexually-reproducing organism] could divide once asexually, then the two daughter cells could reproduce together sexually.

No second individual is even required if an organism is capable of both asexual and sexual reproduction (as the first sexual reproducer undoubtedly was): the organism can asexually create its own mate! (Remember, this is before specialized, complementary sexes had evolved.) In fact, the one organism could divide asexually a million times over, producing an entire population of organisms with which it could then fuse to create recombinant daughter genomes.

-----

Again, you simply do not need specialized parts to perform a function. Function very often predates specialization.


-Bluejay

Darwin loves you.


This message is a reply to:
 Message 62 by heygabbagabba, posted 11-29-2008 7:21 PM heygabbagabba has not yet responded

  
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