I thought this was really neat:
A recent study presented at the annual meeting of the European Society of Human Reproduction and Embryology shows that in the first five days of his existence, the tiniest of human beings has the capacity to heal himself of genetic abnormalities. … Professor William G. Kearns told the annual meeting of the European Society of Human Reproduction and Embryology that a three-day-old embryo (called a cleavage stage embryo) with an incorrect number of chromosomes (known as “aneuploidy”) was capable of undergoing “a dynamic process of genetic normalisation” so that by day five, when it had developed to the blastocyst stage, it had become euploid, with the correct number of chromosomes.
This is a significant development in our understanding of prenatal life. It is also significant because, unfortunately, embryos conceived by in vitro fertilization are often killed if they appear to have genetic abnormalities, a process called pre-implantation diagnosis. The new study suggests that many of these embryos would have grown up to be perfectly healthy, if they were only given the chance.
Sadly, this knowledge has come at a price: the researchers killed at least one human embryo.