Problems with Mutation and the Evolution of the Sexes

I'd like to see if I can help a bit here by giving a very basic, non-mechanistic hypothesis for the development of sexual reproduction into the two-sexes thing we know today.Let's start with one thing here, though: You've used the word "mutation" like this several times, and it's not entirely accurate. The word "mutation" refers only to a change in a gene, not to something that's different. It's likely that several mutations contribute to the transition between asexual and sexual reproduction.Now, on to the hypothetical scenario:Some organisms are isogamous (meaning that both types of gametes are identical--this is generally considered more "primitive"). Then, there are some that are anisogamous (meaning one gamete type is bigger than the other). Then, there are oogamous (oh-AH-guh-muss) types (egg and sperm--this is generally considered more "derived").In some simple, single-celled organisms (such as algae), two cells (constituting two organisms) could feasibly combine into one with twice the genetic material of the former two, giving it added flexibility in the face of a pathogen (i.e. if one of the two genomes had a defective gene, the other genome's copy of that gene could cover for it). You can see how this would be beneficial? Perhaps this wouldn't include two cells completely fusing, but one cell transferring a copy of genome into the other.Later, multicellularity could come around, and certain cells (with only one genome, instead of two--this is called "haploid") specialize in breaking away from the organism and fusing with other gamete cells to produce variation. This is what would be considered "isogamous." Eventually, the multicellular organism could produce tissues, which could produce organs, which could specialize in producing haploid gametes.Providing care for one's offspring is also beneficial, wouldn't you agree? So, if an organism in a gene pool develops a pouch in which it's gametes could be kept, and gametes from other individuals could enter and fuse there, this would also increase the offspring's chance of survival, right? So, retaining gametes would be favorable to letting them loose in the cruel world.However, if everybody retains their gametes inside themselves, how would the gametes find each other? Under these conditions, someone whose gametes can go out and find gametes that are retained would have an advantage. Thus, swimming gametes (sperm) are formed, going after the retained gametes (eggs), and we now have the two sexes that we are currently familiar with.This may or may not be the way it actually happened, but it's reasonably close, at any rate, and it provides a simple background for the general process. This pattern of isogamy--anisogamy--oogamy can actually be seen as you follow certain branches of the evolutionary tree of the algae. I didn't propose any mechanisms, but the mechanisms are generally mutation and natural selection.Feel free, other evolutionists, to add to, alter or clarify anything in this little scenario. Likely, there are other, sub-cellular factors to consider before the "two cells fusing" phase I listed first (such as lateral gene transfer, as mentioned a few times in this thread), but this is generally where our current knowledge is still in its infant stages.Edited by Bluejay, : I wrote "genders" where I should have written "sexes": I did this for the sake of molbiogirl's sanity.

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There was a point to this [post], but it has temporarily escaped the chronicler's mind. -modified from Life, the Universe and Everything, Douglas Adams

Hi, Godservant! Welcome to EvC! Does the possession of intelligence automatically bestow upon you all knowledge? Of course not. There is a phenomenon called "constraint": you can only work with the tools you have available to you. We obviously don't have the tools (or the knowledge) available to us to create a cell from a blob of goo. But, we're working on that; sooner or later, "some very intelligent scientist somewhere" will do it. However, like all knowledge, it takes time, even for "some very intelligent scientist," to find it.Side Note: this is off-topic here. I probably shouldn't have responded, but I didn't want to leave it hanging. You should read the Forum Guidelines: they enforce those here. Maybe you could propose a new topic for this (in the forum labelled "Proposed New Topics" under "Board Administration"). I think this topic has probably been discussed before, so you can look through the archives for it, then decide if you have enough remaining issues to start a new topic.Have fun here at EvC!

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I'm BluejayDarwin loves you.

Click the "Peek" button at the bottom of this message to see the dBcodes I'm using.You can quote prior message like this: Other quotes can be done like this:

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Using these makes it easier for people to see what you're responding to and what you're writing yourself.Now, addressing your post: He didn't say this: please read more carefully. He said our reproductive processes are imperfect, which means mutations (i.e. changes) happen. A mutation causes something like hair color to change. Over long periods of time, the effects can accumulate. There isn't just a random smattering of traits thrown together to form the offspring: most of the genome is conserved when passed from parent to offspring.P.S. These messages are all quite old now: you probably shouldn't go through and respond to them one by one like this.

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I'm BluejayDarwin loves you.

Recessive genes only happen in organisms with two copies of each chromosome. Bacteria do not have two copies of chromosomes: diploidy (having two chromosome sets) is an after-effect of bisexual reproduction. In organisms that only have one copy of each gene (haploid), all genes are expressed equally. If one gene is dysfunctional, the organism cannot express that trait properly, which can very often be detrimental.However, in diploid (sexually-reproducing) organisms, which have two copies of each gene, a dysfunctional gene can be covered if the other copy of that particular gene is not dysfunctional. Thus, the dysfunctional copy is what we call "recessive," and the properly-functioning copy is what we call "dominant."The bisexual condition may have been selected for because of its ability to mask detrimental and lethal recessive genes by providing a second, working copy of the gene. The downside is that it is less effective at removing those recessives from the gene pool. That pretty much sums up the point of this thread.So, when you say: and remember that bacteria can still do things we can't do: there is no "greater" and "lesser" in evolution, and there is no "apex."

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I'm Thylacosmilus.Darwin loves you.