Imagine that mad scientists defied nature and violated the barriers between species. They injected human DNA into non-human creatures, altering their genomes into chimeras--unnatural fusions of man and beast. The goal of the scientists was to enslave these creatures, to exploit their cellular machinery for human gain. The creatures began to produce human proteins, so many of them that they become sick, in some cases even dying. The scientists harvest the proteins, and then, breaching the sacred barrier between species yet again, people injected the unnatural molecules into their own bodies.
To understand why this is not science fiction--and why it's not as horrifying as it sounds--read my latest post over at the Scienceblogs book club.
[Picture: "The Young Family," by Patrician Piccini (2002-3). Wikipedia]