According to Wikipedia, the Chicken has a population of approximately 24 billion. (Making it by far, the most populous bird and potentially the most populous non-rodent vertebrate on earth). Cows are estimated to number upwards of 1.3 billion individuals. Common sheep number over a billion.
If the point of evolution is to propagate and thrive as a species, to become more healthy as a population and continually increase your numbers, then all these species have netted an evolutionary advantage from being tasty. Any species that is commonly utilized by humans for food has survived, propagated, increased in numbers and become more healthy as a population.
So quick.. does anyone know a really great Panda recipe?