NPR Talk of the Nation Science Friday had a feature about how hunting and fishing rapidly affect the evolution of the species in question in a negative way, since hunters and fishermen like to take the big fish or animals. Well bang the drum. How obvious is that? In forestry, we see that in high grading/selective cutting, when people cut out only the biggest trees. The young man did a good job of describing the problem, but the program in general did a bad job of prescribing a solution.
Nature is profligate. That is the basic assumption of evolutionary theory. Many more individuals are born than can survive. Human activities rapidly select for particular characteristics and we have been doing it for a long time. That is why a miniature poodle doesn’t much look like a wolf or a cow has only passing resemblance to aurochs. (The last recorded wild auroch, BTW, died in Poland 1627.)
Game keepers and river keepers have long recognized the problem with taking the biggest and best and leaving the runts to reproduce. The same goes for forestry. The way to go about managing for this is to make sure you take out the undesirable traits too, or in greater numbers. It requires more work and understanding. In forestry, for example, the biggest trees are not always the oldest. You have to harvest the small ones too or maybe even more. Down on my tree farms, the hunters are members of Quality Deer Management association. Fortunately, their task of improving the deer herd is made much easier by the deer population explosion. In the case of deer, for example, the worst thing you can do for the health of the herd is to limit hunting.
Not all species are as common as deer, but some of the same management principles apply. You don’t improve the total herd/forest/school by protecting all individuals equally. In a wild population, you are probably looking to increase genetic diversity. This makes the species more robust. Remembering the nature if profligate maxim, you might improve the genetic diversity AND in the long run the numbers of a species by disproportionately eliminating individuals with particular sets of characteristics. This creates room for the others.
When dealing with the natural world, many things seem counter-intuitive.