The possibilities of genetic engineering continue to grow. May a Jewish scientist genetically engineer things?
Genetic engineering has been cited by some as both halachically acceptable and problematic in several respects:
Not at all. As the Yerushalmi (Nedarim 9:1) asks rhetorically:
As for the reason for the prohibition on kil'ayim, no one claims to have the definitive answer. It is not considered a moral imperative, but rather a chok; a rule without a known reason. We can speculate from here till tomorrow - as Maimonides does in his guide - but it's only speculation. When it comes to deciding halachic matters, such speculation without proof has no place.
Genetic engineering is even worse in this regard since you are completely changing the organism.
But this needs to be tempered with the knowledge that virtually nothing we eat today is like Hashem made it. The wheat we eat today is completely different from what they ate in ancient times. (They ate what we call wild Emmer wheat, we eat durum wheat hybridized with goat grass.) The wheat has changed to the point that it can not even self propagate - it requires humans to plant it. (This change is why ancient Matzah was soft like pita, and ours is hard.)
Our cows are much much larger than theirs, same for chickens and turkeys. (Interestingly modern turkeys also can not reproduce on their own.)
The soft corn we eat did not exist in the past. (And to continue the theme, soft corn also can not propagate on its own.)
In fact, I feel pretty confident in the saying that not a single vegetable in the supermarket is like Hashem made it - and not minor changes either. Major differences in the taste, size, how long it takes to grow.
But, all this needs to understood in light of the question of how much change is called change.
After all, it is permitted to graft together plants together if they are of similar species. For example the wheat hybridization I mentioned above is permitted.
So, in that light the plants and animals we eat have not changed enough to be called new species. And genetic engineering usually limits itself to small changes, which are not enough to make a new species.