I remember learning that the reason you don't eat milk with beef is because you shouldn't cook a calf in its mother's milk. However, when you are dealing with two different species, this same logic doesn't seem to hold. Is there another explanation for why this isn't kosher?
The Torah's prohibition of cooking a young animal in mother's milk, as stated above, applies to mammal's meat in mammal's milk. Rabbi Samson Raphael Hirsch writes that meat is about taking, and milk is about giving.
As birds don't have "mother's milk", there is no Biblical prohibition on chicken-cooked-in-milk. However, the rabbis of the Talmud prohibited it, for fear of mistakes. This distinction is an important one when understanding Judaism, and is stressed by Maimonides.
Well, m'doraita it is applied to all meat and all milk from animals similar to goats (domesticated, kosher animals like cows and sheep, but would exclude foul, fish, and non-domesticated like deer and no-nkosher like pigs). The passuk just mentions it that way because that was a common way of doing it. Chazal darshen three issurim from the three times it appears in Chumash
- The issur to cook meat and milk together
- The issur to eat meat and milk cooked together
- The issur to benefit from milk and meat cooked together (Such as selling meat cooked with milk.)
Chazal also made additional laws on top of the basic laws of the Torah to prevent people from making mistakes. Rabbi Yose haGalili permitted milk and chicken to be cooked together, because chicken is a bird and the law of the Torah is about four-legged animals. Rabbi Akiva disagreed and throught people could get confused between different kinds of meat. Halakha is like Rabbi Akiva.
I'm not Jewish, but I always assumed the 'reason' for all Jewish food laws is 'because god says so!' If you're looking for any other rationalisation, you're missing the point. There's nothing uniquely unhealthy about pork or lobster, but god says don't eat them, so don't! Yeah, there's symbolism of life and death with milk and meat... But that doesn't stop Jews (or others) eating eggs, or killing and eating young animals. Basically, if you expect god to justify his commandments before you follow them, you're not respecting his will.