I agree with the original poster, that sex is one way of proving macro evolution could not be. In order for the evolution to work both sexes male and female would have to evolve simultaneously in just one lifetime or the whole thing would crash and would have to start over with the next generation knowing exactly what both wanna be sexes are trying to accomplish. Thats a lot to ask to have to produce sex organs that fit a delivery system that works for both and a proper incubation system in the female all in just one lifetime. Then to consider how they could do all this and have one side have half the dna and the other side have the other half to then join in making a baby. The odds must be astronomical.
Why Sex??
by PopeOfEruke 48 Replies latest social relationships
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bigmac
off topic----
i like reading some of these old threads--simply to see usernames we never see now. i wonder if many still read this site ?
think of all the changes we've had in the last 9 years--especially in the techno world.
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LisaRose
Well I was hoping Cofty or someone else who has a good understanding of evolution would have comments on this, as I have never looked into it or thought about it. Still, I don't understand why you think sex proves we couldn't have evolved. It seems no different than any other characteristic that gives an evolutionary advantage.
You say that sex would have to evolve in one generation but that simply is not true, at least not for sex as we know it. Sex began very early in evolutionary history and started with very simple organism, not with animals or people as you seem to think. Plants have sex. Sex, in its simplest form is just two organisms that combine to produce offspring with a combination of DNA from both parents.
From my very superficial knowledge of the subject, sex is useful because it combines the DNA of different organisms. One aspect it that two beneficial mutations (from two different individuals) can combine in one individual, giving that individual an evolutionary advantage. The other side of the coin is that two non beneficial mutations can combine in one organism. That organism will then be more likely to die out before reproducing, thus the bad mutations die out.
Originally sex was simple, but as organisms evolved into more complex beings, sex evolved as well. Anything mutation that made sex more likely was retained, any mutation that made sex less likely was lost.
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zound
I'll add a few comments / examples, maybe those with greater knowledge could weigh in:
There is an example of two fish species in ponds in mexico that are very closely related but one species reproduces asexually, and the other sexually. These fish are victims of parasites that are in the ponds which attack them and cause them to get sick - also the parasites produce black spots on the fish as a byproduct.
The fish that reproduced asexually were targetted almost exclusivley by the parasite because all they did was clone themselves, not introducing new genes and dna into the mix. Mutations occurred relatively rarely because of this - so the fish were not able to adapt to protect themselves from the parasites.
The fish that reproduced sexually however were constantly mixing dna, and causing more mutations and adapted to fight off the parasites better.
A drought hit the ponds and cut off a section of it. In this section the sexual reproducing fish soonafter became targetted by the parasite - which at first puzzled scientists. It turned out however that these fish had a very small pool of dna to share and were in effect "inbreeding" - swapping the same dna amongst themselves almost like the asexual fish. The scientists took a bucket of fish from another cut off pond - pored them in, and a year later the fish population was again fighting off the parasites - due to new dna thrown into the mix from the new bucket of fish.
Sexual reproduction mixes dna, and causes higher chance of mutations. As to how it began I'll describe part of that later - my knowledge is a little patchy on this, which is why I bumped this thread.
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zound
Sex began because of the advantages of mixing dna (for reasons I described in part above). The ins and outs of how that evolved over time (pardon the pun) I only know bits and pieces.
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LisaRose
Crazy guy, another thing I want to comment in is that the "odds must be astronomical". But when we are talking abut evolution, the odds ARE astronomical, in a way, but you are talking about millions of organisms over millions of years. If you think about the lottery, YOUR chances of winning are astronomical, but the odds that SOMEONE will win are not, eventually someone wins. Say there are a millions of fish, all who reproduced a sexually. If a fish had a genetic mutation that allowed it to combine its DNA with that of another, that mutation would give its offspring a better chance at survival, because combining DNA usually favors survival.and the mutation doesn't have to be as impossible as you might think.
Fish produce eggs, which are expelled and then fertilized by the male. I had a Pond once and the pond comets reproduced very rapidly, we had five comets in May, 45 in July. The female would become fat with eggs, and the male would become very interested, following the female and judging her sides, which caused the eggs to come out for him to fertilize. It's pretty simple. So, prior to this kind of reproduction, the fish would have both eggs and sperm which combined within itself ( I am guessing here). Anyway, going from asexual to sexual reproduction is not that big of a change here, and when you are talking millions of years, not impossible at all.
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Apognophos
Good comments. Another way of looking at it is that sex is just one means of carrying on genes; since this is arguably the purpose of life, we shouldn't be surprised that there are multiple pathways for doing this. Look at viruses: they reproduce without even being alive. For all we know, viruses invented sex. See this article for all kinds of examples of asexual gene transfer: Horizontal gene transfer
Also, I believe the flaw in Crazyguy's thinking is that there is a black-and-white line between "can reproduce together" and "cannot reproduce together". None of us are perfectly in sync genetically -- especially when we cross racial lines to make beautiful mixed babies -- and that doesn't prevent reproduction in any way. There are all sorts of "levels" of evolutionary development in each of us; e.g., some of us have lactose tolerance because our ancestors raised cattle, and some of us don't, like most mammals, who no longer need it once they reach adulthood.
In fact it's the opposite of "unlikely" that a species would "stay in sync" from generation to generation. It's quite likely, as they are sharing genes and thus can never deviate too far from each other. That being said, populations that are separated eventually diverge genetically and do lose the ability to reproduce together. The ones that stay together, though, are practically bound to stay in sync evolutionarily.
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cantleave
The ability to mix genes is an important tool for ensuring genetic variation and the phenotypic diversity that ensues. Such diversity provides a number of advantages, one of which is the ability to fight off attacks from constantly evolving strains of parasitic diseases.
When a new strain of parasite arises the "host" population needs to develop a immuno response in order to fight it. A host species that reproduces by sexual reproduction can rapidly produce individuals with the capability to resist the new strain. Unfortunately as the population of the resistant host individuals increases, some of the parasites will develop methods for breaking down the host defenses and as these increase the disease becomes prevalent within the population. So in effect a race ensues, the parasite and the host populations have to adapt in order survive. Sexual reproduction gives the host a massive advantage, allowing for greater genetic diveristy and faster adptation.
In comparison, asexual populations can only evolve resistance to a disease if a random alteration in a gene, arises. Since these types of mutations are very rare, an asexual population would have great difficulty keeping up with the disease.
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cofty
Some great answers above. I thought it might be good to start a new thread looking positively at the topic of sex from an evolutionary point of view.