historical
constraints (such as the blind spot in the vertebrate eye) and the simultaneous evolution of other organisms, such as
predators and diseases, engaged in a constant arms race to run faster or to overcome immune resistance.
the equivalent of changing a propeller plane into a jet airliner one step at a time, while ensuring that each intermediate
step is not only airworthy but actually flies better than the previous step (Jacob 1977). Nature cannot ‘go back to
the drawing board’, find some new genetics and have a break while the new design is tested and perfected.
Everything has to be done on the fly, based on the mutations that happen to be around at the time and in the full glare of
competition from other animals. Artificial selection has the advantage that some of these constraints can be relaxed
(Sandøe 2010). It is possible to import new genetics, for example, and to greatly increase the range of mutants that
selection has to work on. We can keep animals alive that would die in nature (such as ones that need our help in
mating) and there is also a sense that we are beginning to literally go back to the drawing board and ‘design’ animals
for the goals we want. We can hope to produce animals with traits and combinations of traits that could in the end be
successful and have high welfare, but which would never have been possible in the wild.