For as long as animals have been domesticated, people have been actively changing how they look and perform.
Size, color, body shape, milk production, and many other traits have been tinkered with in efforts to produce "better" animals. We would like to think our selection processes have improved the value of our animals. Whether this is true or not is determined primarily by how much emphasis we place on which traits.
The process can go wrong in several different ways but the main problem will usually be a poor understanding of what makes money and what does not. The current population of oversize cattle – bred to fit the box and meet the demands of the trade – is an example. These animals are poorly suited for production as grazing animals, yet at least two thirds of their slaughter weight and probably 90% of their parents' mature weight will be grown on grass.
Selecting for traits of low importance reduces the ability to select for more important traits. Even more damaging is selecting for the wrong traits.
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