Nature can produce organisms with new gene
combinations through sexual reproduction. A brown cow bred
to a yellow cow may produce a calf of a completely new color.
But reproductive mechanisms limit the number of new combinations.
Cows must breed with other cows (or very near relatives).
A breeder who wants a purple cow would be able to breed toward
one only if the necessary purple genes were available somewhere
in a cow or a near relative to cows. A genetic engineer has
no such restriction. If purple genes are available anywhere
in nature-in a sea urchin or an iris-those genes could be
used in attempts to produce purple cows. This unprecedented
ability to shuffle genes means that genetic engineers can
concoct gene combinations that would never be found in nature.