Why genders?

[Leçi]

It all started with one celled organisms that just devided, over time organisms became more complex and so did reproduction. But why did alot of animals evolve to have a male and a female version. It's quite a weird way to reproduce if you look at and in some cases just plain dangerous and overly complex. So are there any theories that explain why there are genders and why we can't make ourself pregnant or devide which seems like a easier safer way.

 

[nemesiss]

diversity.

if you reproduce a sexually, then you run the risk that the whole population will be wiped out be a simple little virus.
with genders, you have a smaller risk that a whole population is wiped out.
that doesn't mean that it can't, just that the odds are smaller.

 

[Leçi]

That's true. The difference between sexual and asexual reproduction is quite big I think. Are there any theories how it came to be?

 

[RichardMNixon]

http://en.wikipedia.org/wiki/Evolution_of_sexual_reproduction#Two-fold_cost_of_sex

Evidence that the cost is not insurmountable comes from George C. Williams, who noted the existence of species which are capable of both asexual and sexual reproduction. These species time their sexual reproduction with periods of environmental uncertainty, and reproduce asexually when conditions are more favourable. The important point is that these species are observed to reproduce sexually when they could choose not to, implying that there is a selective advantage to sexual reproduction.

That suggests that it's certainly beneficial, but it looks like there's multiple explanations as to why.

 

[Dean]

It all started with one celled organisms that just devided, over time organisms became more complex and so did reproduction. But why did alot of animals evolve to have a male and a female version. It's quite a weird way to reproduce if you look at and in some cases just plain dangerous and overly complex. So are there any theories that explain why there are genders and why we can't make ourself pregnant or devide which seems like a easier safer way.

I think you should be careful not to confuse the scientific term "sex" and the overtly unscientific word "gender". The differing - male and female -sexes are a product of evolution by natural selection, and are markedly identified via anatomical or physiological/psychological differences. The concept of "gender" is a social construct.

If you are speaking of the origin of "sexes"; I think you may need to concentrate more on the issue of the evolutionary origin of sexual (rather than asexual) reproduction, since this is undoubtedly why this male-female system was created, far back enough.

In which case ... it is worth noting that at the time when life was merely unicellular, the proportion of genetic material in the genome would have steadily increased with the repetitive frequency of gene-duplications over geological timescale, and as it did, the range of enzyme functions in the DNA would have proliferated. And so; mutations that increased the variation and length of gene replication would have been acted upon by naturally selective pressures. And this would include sexual reproduction.

And as for asexual reproduction being less risky than sexual reproduction, and asking about species that have this mechanism ... well, some do! Take Varanus komodoensis (Komodo Dragon). This animal has the versatility of being able to reproduce both sexually and asexually, depending on whether or not males are readily available, and yes, this may well be quite a significant survival advantage. The same applies to some species of amphibian, when faced with a single-sex environment. However, this method can also be problematic, since in asexual reproduction, no genetic recombination occurs, and thus, all offspring of the mother would be genetically identical to the parent, leaving NO room for genetic variance (and hence natural selection) of any kind, other than in (random) mutations. They are called clones. Asexual reproduction comes in four forms; fission, budding, gemmulation and fragmentation. In fission, an organism divides into two (binary fission) or more (multiple fission) new organisms that will all grow into an approximate copy of the parent. A budding organism produces (e.g. the Hydra shown in fig. 1) its offspring as a smaller outgrowth on its body; it is an unequal division of the parent. Gemmulation is when an organism "sets aside" living cells within a hard capsule, a gemmule, to grow when circumstances next become beneficent. Finally, fragmentation occurs when a multicellular organism is divided into smaller parts, which then grow to form complete new individuals.
The greatest strength of asexual reproduction is that it allows for extremely rapid procreation. Populations can increase in size very quickly, and only a single individual is needed to colonise a new area. Asexually reproducing organisms are incredibly abundant and all other forms of life depend on them as the base of the food web.
However, the fact that the population will consist of clones, with no genetic recombination occurring, can make the population very sensitive to changes in the environment and thus more prone to extinction. Also, as asexually reproducing organisms will evolve through genetic mutation only, it is difficult for them to regain advantageous genes lost from deleterious mutations. They can only regain them through back mutations which is rather unlikely. Thus such deleterious mutations tend to accumulate over time. This is called Mà¼ller's ratchet and does not apply to sexually reproducing organisms.

Essentially, asexually reproducing organisms evolve by the same processes as sexually reproducing ones, MINUS the genetic recombination. This is very simplified though - many bacteria, for instance, often exchange genetic material in the form of plasmids, small strings of DNA that can pass through a small channel that bacteria can form between each other. These plasmids can contain genes that carry fitness benefits - for instance, resistance to an antibiotic. (Plasmids are often used in microbiology/genetics labs for various purposes. They're very handy.)

 

[Prolescum]

I think you should be careful not to confuse the scientific term "sex" and the overtly unscientific word "gender". The differing - male and female -sexes are a product of evolution by natural selection, and are markedly identified via anatomical or physiological/psychological differences. The concept of "gender" is a social construct.

Not wishing to distract from your answer to the OP, but the word gender is perhaps better understood in languages other than English, as we often only use it to refer to sexes or, at a stretch, grammatical attributes (and sometimes confuse the two), but its meaning is synonymous with type or class so I would say it's valid to use in this context.

 

[Aught3]

I'm slightly unsure as to whether the question in the OP is 'why sex?' or 'why sexes?' The first question has been answered fairly decently by pointing out the advantages to shuffling genetic information from one generation to the next. The answer to the second question most likely has to do with the extra-nulclear genetic elements which are carried by organelles such as mitochondria and chloroplasts. If the two parents simply merged, there would be a selection pressure for the genes in these organelles to kill off the organelles from the other parent and be the sole survivor ready to go into the next generation. The result would be the death of most of these critical organelles giving the new organism a slow start in life. So a compromise is reached where one parent donates the organelles (female) and the other does not (male). This provides the new organism with all the organelles it needs without having to experience the costly arms race.