(November 13, 2014 at 1:05 am)Reader Wrote: The next question: (we now understand why we didn't evolve into 7 or 7000 "sexes") ... is at what point did we go from being asexual to being sexual (2 sexes) in order to reproduce?A long time before humans, and in fact many species continue to reproduce asexually, and some species that do reproduce sexually can in fact self-reproduce asexually (e.g. some sharks). If we were to take sharks as an example, one could well argue that there wasn't fixed a "point" when a species switched to sexual reproduction, but rather that at some point it became available as a means of reproduction, and that overtime evolution geared towards sexual reproduction.
In the case of humans and other mammals, we rely solely on sexual reproduction. So the the role of asexual reproduction was diminished, ultimately to the point that asexual reproduction no longer provided a meaningful function to the species and it was dropped. We are unable to initiate parthenogenesis naturally and reproduce asexually, although at some point in the past one of our biological ancestors would have been able to (for reference that process means the female's ova self-conceives producing an embryo genetically identical to the mother). So in the same way that we can no longer use our appendix for anything, we also can no longer use our original means of asexual reproduction.
The other thing to consider is that male and female sexes were not originally assigned by genetics, and as I previously mentioned it is still the case for many species that environmental factors and not genetics determine whether an organism develops into a male or a female. This is obvious simply by the fact as I previously mentioned that the ZW sex chromosomes determine sex in exactly the opposite way of the XY sex chromosomes.
So in short the answer is that the "point" you're enquiring about refers to a time perhaps millions of years ago when sexual reproduction began to be trialled alongside asexual reproduction, and overtime evolution generally geared towards sexual reproduction producing the modern species we have today that are now unable to asexually reproduce.
Hope that helps.
For Religion & Health see:[/b][/size] Williams & Sternthal. (2007). Spirituality, religion and health: Evidence and research directions. Med. J. Aust., 186(10), S47-S50. -LINK
The WIN/Gallup End of Year Survey 2013 found the US was perceived to be the greatest threat to world peace by a huge margin, with 24% of respondents fearful of the US followed by: 8% for Pakistan, and 6% for China. This was followed by 5% each for: Afghanistan, Iran, Israel, North Korea. -LINK
"That's disgusting. There were clean athletes out there that have had their whole careers ruined by people like Lance Armstrong who just bended thoughts to fit their circumstances. He didn't look up cheating because he wanted to stop, he wanted to justify what he was doing and to keep that continuing on." - Nicole Cooke
The WIN/Gallup End of Year Survey 2013 found the US was perceived to be the greatest threat to world peace by a huge margin, with 24% of respondents fearful of the US followed by: 8% for Pakistan, and 6% for China. This was followed by 5% each for: Afghanistan, Iran, Israel, North Korea. -LINK
"That's disgusting. There were clean athletes out there that have had their whole careers ruined by people like Lance Armstrong who just bended thoughts to fit their circumstances. He didn't look up cheating because he wanted to stop, he wanted to justify what he was doing and to keep that continuing on." - Nicole Cooke
