Two people reproduced 7 billion people.

[festive1]

The first creatures to develop sexual reproduction were not as complex as a human being. The more basic the organism, the less there is to fuck up. There's no proof that I am aware of... yet... See, that's the joy of science, it keeps advancing and incorporating new information as it becomes available. Perhaps the origins of sexual reproduction will never become available, as we are likely talking of microscopic forms of life that existed millions of years ago. It's still better than your theory that two perfect people populated the world.

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This was bugging me, but a quick google search brought this up:

Many organisms can reproduce sexually as well as asexually. Aphids, slime molds, sea anemones, some species of starfish (by fragmentation), and many plants are examples. When environmental factors are favorable, asexual reproduction is employed to exploit suitable conditions for survival such as an abundant food supply, adequate shelter, favorable climate, disease, optimum pH or a proper mix of other lifestyle requirements. Populations of these organisms increase exponentially via asexual reproductive strategies to take full advantage of the rich supply resources.
When food sources have been depleted, the climate becomes hostile, or individual survival is jeopardized by some other adverse change in living conditions, these organisms switch to sexual forms of reproduction. Sexual reproduction ensures a mixing of the gene pool of the species. The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. The meiosis stage of the sexual cycle also allows especially effective repair of DNA damages (see Meiosis and Bernstein et al.[11]). In addition, sexual reproduction usually results in the formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, eggs, pupae, cysts or other "over-wintering" stages of sexual reproduction ensure the survival during unfavorable times and the organism can "wait out" adverse situations until a swing back to suitability occurs.

Seems like a probable link to me... organisms that can reproduce both sexually and asexually as needed, handy. Sexual reproduction is great for diversity. Asexual reproduction is better for population numbers.
http://en.wikipedia.org/wiki/Reproduction