The messenger.

According to the Cayce readings, when some of us spirits were in the process of getting enmeshed in the Earthly dimension we interfered with the structure of physical things by the use of our creative ability.
The result of this was, for example, trees with arms and anatomically mixed animal forms some of which included aberrations of the then human form which we had created for our use on Earth.
The Cayce readings further stated that in Atlantean times scientists had developed methods of surgically correcting such aberrations which, by then, had become inherent in humans, and were applying them as a matter of course in special institutions.
It does not take much to equate the motivation behind the initial interference with that of scientists of modern times in their work in genetic engineering, stem cell use and the like. Similarly it does not take much to equate the results in the past with possible results in the future.