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Why makes organisms reproduce?

I don't mean to linger on the philosophical point of this question but more on the biology of it.
In species other than humans and a few others, sexual reproduction is not something done for pleasure so why do other species do it? It provides no benefit for that particular organism. Many people have answered that it's just a passed down trait or it has to do with genetics. I don't understand how a habit can be passed down through genetics. This isn't something like the need for an organism to feed itself, because in that situation, the organism would die otherwise. With sexual reproduction, there is no benefit (that I can see) for the organism.
Which leads me to another question: why do females (of species other than humans, once again) find males with better reproduction rates, more 'attractive' (as I have learned in my biology class). It doesn't mean higher survival rate, so once again, how would that organism be affected and how does it make that decision?


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  • Apr 17 2013: If you'd like an explanation (in terms of biology), then Nick Lane's book 'Life Ascending' attempts (quite well) to explain why and how sexual reproduction evolved. His book details 10 great 'inventions' of evolution, with sex being one of those inventions. It's worth a look to get some detail about evolution.

    This is a small sample of an article he wrote in 2009:
    "Sex is absurd. It costs a small fortune to find a partner, transmits foul venereal diseases and parasitic genes, and randomises successful allele combinations. Worse, sex requires males, viewed by implacable feminists and evolutionists alike as a waste of space. Why we all have sex anyway was seen as the queen of evolutionary problems in the 20th century. Recent work shows that over time all complex species would degenerate, like the Y chromosome, without sex. The details help explain why sex first arose, enabling early eukaryotes to thrive."

    As others have said, sex is costly to the individual but beneficial to the species. As I understand it, mixing genes gives an organism a greater chance of survival, so any species that does that will have an advantage over a species that doesn't mix genes (via sex). So once sex evolved, it provided an advantage to those species that did it t reproduce. Also, something that I understand is important is that sex evolved very early in the history of life (with early eukaryotes). I'm no expert, but Nick Lane is (and it's just a short chapter in a good book!).

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