The Breeders’ Law

An old heuristic I came across while investigating the techniques of plant and animal breeding; more specifically, for maintaining desirable characteristics that manifest in a continuous, normal distribution, those traits that we would likely now call polygenic.

If all members of the population breed, regardless of their manifestation of the trait, the trait will degenerate.  If the 33rd percentile and above successfully breed, the trait will remain constant.  If the 66th percentile and above breed, the trait will improve in the succeeding generations.

There are certain plants that require constant selection to maintain their desirable properties, both because there are wild plants that inevitably contaminate the cultivated types, and because the traits were artificially selected for and tend to revert back to an original state if natural selection is not opposed.  Carrots are a prime example of this.  They are the same species as the weed known as Queen Anne’s lace and will easily interbreed with it.  More importantly, if left to propagate itself, carrot will eventually revert back into a form similiar to Queen Anne’s lace.  The swollen root, often rich in beta carotene, is both an evolutionary disadvantage and an unstable characteristic.  To maintain a population of carrots, each generation must be dug up, examined, and have its unsuitable members removed; otherwise, the desired traits that make carrot a succulent biennial rootcrop diminish and are lost.

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