thanks for keeping me up to date. I will remember this in the future. I was basing my statements off Dolly.Well. I attended and presented research at the last International Society for Stem Cell Research (ISSCR) in Yokohama Japan (June). The research you read about on the Internet is a few years out of date from research presented which is obviously a year or so out of date from bench top work. Yes, the skin, heart, brain, etc... have niches for progenitors. In the brain, for example, these give rise to new interneurons. In the skin those progenitors give rise to skin. This years Nobel Prize (2012) in Physiology or Medicine was awarded to John Gurdon and Shinya Yamanaka for changing adult cells into stem cells; these cells (originally performed using skin cells) can be turned into pluripotent ES cells which can become a new organism (including human, although that research is restricted; except maybe in China). So, to be clear, there is NO NEED for an egg OR a sperm. A single adult skin cell can be reprogrammed a developed in a petri dish into a new embryo that will, if implanted, become a fetus and eventually organism. Oh, and yes, sperm can be made from a skin cells. An "eye" can be grown from a skin cell complete with retinal layers and lens.
That aside, we are still dealing with life arising from complex incubation so its a bit misleading to talk about skin and a zygote offering the same potential, since one has already achieved that potential and the other requires considerable effort (along with many increased likelihoods of failure and imperfection) to come to the same benchmark.
IMHO the notion of designating something life "life" somewhere down the track from conception is arbitrary. I guess the further down the track one goes, the more one requires political language, so "abortion" becomes "tissue removal" etc etcAs for the fetus or late embryo, I just don't think most people are prepared to support pro-choice when confronted with a real life fetus. At 20 weeks we're talking about a 20 centered fully formed human being. Most people have no rational bases for their pro-choice or pro-life support, the decision they make, is made post-hoc of a gut feeling born out of an emotive argument made to them by a media outlet at some point earlier in their life. pretty much like everything else they "think" about.