This reminds me of a story about hen breeding: Selecting the hen who lays the most eggs doesn't necessarily get you the most efficient egg-laying metabolism. It may get you the most dominant hen, that pecked its way to the top of the pecking order at the expense of other hens. Individual selection doesn't necessarily work to the benefit of the group, but a farm's productivity is determined by group outputs. Indeed, f…
We had positively selected chicken for agressivity since 1000 years, we have sumatrans, aseels, old english game, cubalayas, the most vicious animals possible for generations and generations of people. All of these are really terrible layers.
There is a lot of variability in character also between different individuals from the same chicken race.