Genetically Modified Humans
There is a gene found in mice, humans and most other mammals called myostatin. It's function is to keep the body from building too much energy consuming muscle. Deleting or down-regulating this gene produces muscular hypertrophy. CRISPR has already been used to produce super muscled mice, goats, and cattle. Occasional mutations of this gene have produced some breeds of ultra muscled cattle and even, in at least one case, a super-strong child.
With CRISPR, this kind of modification is cheap and easy. For now, most major countries have signed on to protocols that forbid this kind of modification of the human germ line, partly because of the need to make sure such changes do not introduce devastating side effects that could spread through the human race and partly because of the fear that willy nilly tampering with our genome could change us utterly.
There are many terrible diseases that are caused by minute and potentially correctable defects in our genomes, including sickle cell disease, hemophilia, Huntington's Disease, and cystic fibrosis to name just a few of thousands. The technology is already simple and relatively cheap, and it just takes a few steps from in vitro fertilization, which has now become routine.
If safety concerns can be assuaged by more experience and improved techniques, will be be willing or able to resist applying this technology to remove these destructive genes from our genomes? I doubt it. And once we have done that, will anybody be able prevent some from playing god to modify genomes to produce prettier, smarter, people with more economically valuable traits?
These are questions that confront society now, because the technology is already there.
(notes for an eventual review of A Crack in Creation by Jennifer A. Doudna and Samuel H. Sternberg)