Assisted Reproductive Technologies: Evolution of Human Niche Construction?

Until very recently, human life was exclusively sexually transmitted. Mammalian fertilization appears inherently wasteful: hundreds of million sperm are introduced during insemination, yet just a few hundred will survive their passage through the uterus and reach the oviduct (Fallopian tube). Human sperm cannot fertilize an egg without prior conditioning by the environment in the oviduct of the female. After proper conditioning, sperm undergo capacitation, a series of dramatic changes in their membranes and pattern of movement. These changes are required for the final push toward the egg, the penetration of the gel-like cumulus layer surrounding the egg, binding to, and fusion with the egg by a single sperm. Recent insights from reproductive biology are providing clues as to why fertilization involves numerous hurdles in live mammals including humans. Assisted reproduction technologies have made rapid advances and are now used to fertilize human eggs in the laboratory. This is done with sperm exposed to artificial capacitation media or by direct injection of a single sperm into an egg. Early embryos are cultured for up to several days prior to implanting in a mother or surrogate mother. These technologies have allowed millions of parents to fulfill their parenting wish and most ART children appear perfectly healthy. There is some concern that reproductive technologies might have effects on the biology of the children and potentially on subsequent generations. From an evolutionary perspective, it is to be expected that humans would use their technology to manipulate their own fertility. In light of our incomplete knowledge of the processes determining the growth and development of embryos, we should better elucidate the potential effects of bypassing evolved female mechanisms for quality control of sperm and embryos and the potential effects of the biochemical environment in which early embryos are cultured in the laboratory. Negative consequences of freezing sperm, eggs or embryos also deserve better study. Human ingenuity and technology has made it possible to produce children without sex and with the help of third parties. Like all new human technologies, these developments come with the need for important ethical and economical decisions.