Sexual reproduction vs Asexual
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26-04-2011, 01:04 PM
Sexual reproduction vs Asexual
I can't seem to find anything on sexual reproduction vs Asexual reproduction. Considering you have all you need right there with Asexual reproduction, why would evolution evolve sexual reproduction. It just seems counter productive, does it not?
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26-04-2011, 01:45 PM
RE: Sexual reproduction vs Asexual
Asexual reproduction does look quite good, for example a stick insect can reproduce without any energy consuming, and dangerous courtship, that some birds tend to do. But the asymmetry of sexes evolved for a reason. It is spelled out precisely in The Selfish Gene (aka the Holy Bible). In a nutshell: genders evolved because genes for creating two different groups of the same species (genders) created such individuals that were more successful in reproduction. Why? Because they specialized in certain tasks so they could perform them more effectively. Sperms became mobile, and resource-free, while eggs became rare, precious and full of nutriment. The lifestyle, behavior(neglecting memes) and build-up of the individuals evolved parallel to this differentiation. So sexual reproduction is better, because usually it makes reproduction more efficient by allowing different individuals to specialize in different tasks, thus perform them more efficiently, thus propagating their genes more efficiently.

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26-04-2011, 02:01 PM
RE: Sexual reproduction vs Asexual
It also increases the diversity between offspring and parent. In asexual reproduction offspring are basically clones of parents whereas in sexual reproduction there is diversity in genetic information. Here is a hypothetical situation. If an organism survives until reproduction then it has a good survival probability. If that organism asexually reproduces then its offspring should have a similar chance of survival since it is more or less identical. That is only if the environment in which it lives is not changing. If the environment changes then its survival probability may go up or down and that will make it more difficult on that lineage and possibly that species because genetic diversity is low. In a sexually reproducing population the offspring's survival probability may vary from its parents but that lineage is increasing its genetic diversity so that if the environment changes then that lineage may have enough diversity to survive.

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26-04-2011, 02:29 PM
RE: Sexual reproduction vs Asexual
The in that case, what is the purpose of stopping at 2 types? Why not 3s genders? Or 4? Considering evolution has no limits, nor an actual plan, if 2 increases efficiency then shouldn't more?
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26-04-2011, 02:38 PM
RE: Sexual reproduction vs Asexual
(26-04-2011 02:29 PM)NotSoVacuous Wrote:  The in that case, what is the purpose of stopping at 2 types? Why not 3s genders? Or 4? Considering evolution has no limits, nor an actual plan, if 2 increases efficiency then shouldn't more?

good point. Take yeast as an example. Some species have up to 36 sexes! This is a very good question that I have given a lot of thought to but I still come up short. Perhaps multiple sexes evolved very early in some lineages but the most efficient method was just with two. From this lineage the Eukaryotes arose and then gave rise to the Metazoans. Maybe sex evolved multiple times over the course of early life and the two sex lineage was simply able to adapt more quickly and efficiently. It is also interesting to note that there is some good theory behind the development of sexes. The amount of energy that men and women expend on production of gametes is roughly equivalent but the products are vastly different, egg and sperm. For men the production of thousands of small gametes is more beneficial than the production of hundreds of larger gametes. For women it is more beneficial to produce one large egg rather than two medium-sized eggs. This topic always gets my brain going...I may think about this the rest of the day!

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26-04-2011, 02:42 PM
RE: Sexual reproduction vs Asexual
Here is a lecture I watched a while ago talking about sexual selection, I hope it isn't too complex or rudimentary for your liking.

Why stop at 2 types? No more is needed or evolved (although, we do have mixes of the 2 sexes.) Evolution does have limits. It takes time, and can only work with what it has and with the resources (such as energy in the form of ATP) it can get. Also, more than 2 may make the system too complex for the species' benefit. If someone could point out a species with more than 2 ordinary genders, it would be appreciated.

@Bearded Precisely where I would have gone. =]

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26-04-2011, 02:48 PM
RE: Sexual reproduction vs Asexual
(26-04-2011 02:42 PM)daemonowner Wrote:   Here is a lecture I watched a while ago talking about sexual selection, I hope it isn't too complex or rudimentary for your liking.

Why stop at 2 types? No more is needed or evolved (although, we do have mixes of the 2 sexes.) Evolution does have limits. It takes time, and can only work with what it has and with the resources (such as energy in the form of ATP) it can get. Also, more than 2 may make the system too complex for the species' benefit. If someone could point out a species with more than 2 ordinary genders, it would be appreciated.

@Bearded Precisely where I would have gone. =]

This is a really intriguing question that I asked my students in Paleobiology Lab. I was first introduced to this question last semester in an evolution class and it really made me think. 2 sexes is the simplest system for sexual reproduction but 3 sexes increases diversity. Another intriguing point hidden within this is the switching back and forth between sexual reproduction and asexual reproduction. Cnidarians (jellyfish, sea anemones and corals) go through asexual periods of reproduction (the sea anemone phase of budding) and then sexual periods (the jellyfish stage). Sexual selection and reproduction are not trivial subjects, and I love it!

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27-04-2011, 08:13 AM
RE: Sexual reproduction vs Asexual
Probably the 2 sex system is good because finding a mate takes energy. If you find an ideal mate it requires X amount of energy (and time). If you have to look for 2 mates because your species has 3 sexes (supposing that all of the 3 kinds are needed to have sex), it takes X^2 energy, plus the energy you need in order to keep your first mate during you are searching for the second. Maybe it isn't worth it.

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27-04-2011, 09:26 AM
RE: Sexual reproduction vs Asexual
I like sexual reproduction. It is one of my favorite activities.

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04-05-2011, 05:55 PM
 
RE: Sexual reproduction vs Asexual
Well, sexual reproduction works perfectly if environmental conditions are optimal. In fact, some animals are able to switch back and forth between sexual and asexual reproduction and they reproduce asexually when environmental conditions are good; food is abundant, weather conditions are good, etc..
But in nature, that's not always the case. So when conditions aren't so great, a population needs genetic variation in order to evolve and adapt to these changes. That's when you'll see some of these animals switch to sexual reproduction.
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