Eli5: Is there any particular reason on why we mostly eat cow/chicken meat instead of other animals? Are these healthier or is there another reason?
In: Biology
No reason in particular, but a complex historic process difficult to research. But the main cause is that we domesticated theses species for long enough for them be widespread and to be versatile an easily adaptable to different environments. The former, obviously, is due to the long domestication. Also obviously, the spread of these species are related to colonization and trade.
There are evidences of chickens in European potteries since the 5th or 7th century, but there are mentions in the Talmud and the Bible’s New Testament dating from the 1st century that are understood as rosters. Also, the roster is a part of the Chinese zodiac, which origin I couldn’t date, but it was mentioned by Confucius in VI century. Again the domestication of chickens is not well understood, but some genetic evidences point to the [junglefowl](https://en.wikipedia.org/wiki/Junglefowl) in the region that nowadays is India as the origin about 8000 years ago. As an easy and cheap source of protein is not difficult to understand how this fowl would easily spread trough Asia and, eventually, though Europe.
Our cows seems to be descendants of to lineages of urus (now a “recently” extinct species) [in the ancient India/Pakistan](https://en.wikipedia.org/wiki/Zebu) and the [ancient Mesopotamia](https://en.wikipedia.org/wiki/Aurochs) domesticated about 10500 years ago. Again, is not difficult to imagine how trade would spread these animals, as they were naturally spread trough a good part of Asia, North Africa and South Asia.
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