> The thing shared by all mechanics of evolution is that they need a population with enough internal variation to be able to move the needle at all. A population that needs to evolve itself out of a corner...
True. In a sense, your metaphor of variation as the fuel of evolution is very apt. Variation is indeed the fuel of evolution, in the sense that evolution consumes it. In order to make your car move, you need the fuel and you need to consume it. When "a population evolves itself out of a corner" it does so by consuming part of its variation. The population survives, the single individuals might be selected out (or single traits, through differential reproduction rates).
> We did not practice eugenics on dogs for millenia -- we selectively bred dogs.
It seems to me that any form of selective breeding when applied to human beings falls entirely into the definition of eugenics. The Merriam Webster defines eugenics as: "the practice or advocacy of controlled selective breeding of human populations (as by sterilization) to improve the population's genetic composition".
> the more narrow the breed is, the less robust it is
Absolutely true, but dog breeds are (especially in recent times) are really extreme and cruel forms of selection. Commercial breeders (and their customers) are following absurdly strict appearance canons. On the other hand, the slightest form of imposed human breeding, however transversal to the bulk of human variation (say, for example, discouraging from reproducing people who are more than 2 standard deviations taller than the rest of their country average or reference ethnicity) is already an ethically unacceptable form of eugenics, independently from its practical impact on the genetic variation of humanity.
True. In a sense, your metaphor of variation as the fuel of evolution is very apt. Variation is indeed the fuel of evolution, in the sense that evolution consumes it. In order to make your car move, you need the fuel and you need to consume it. When "a population evolves itself out of a corner" it does so by consuming part of its variation. The population survives, the single individuals might be selected out (or single traits, through differential reproduction rates).
> We did not practice eugenics on dogs for millenia -- we selectively bred dogs.
It seems to me that any form of selective breeding when applied to human beings falls entirely into the definition of eugenics. The Merriam Webster defines eugenics as: "the practice or advocacy of controlled selective breeding of human populations (as by sterilization) to improve the population's genetic composition".
> the more narrow the breed is, the less robust it is
Absolutely true, but dog breeds are (especially in recent times) are really extreme and cruel forms of selection. Commercial breeders (and their customers) are following absurdly strict appearance canons. On the other hand, the slightest form of imposed human breeding, however transversal to the bulk of human variation (say, for example, discouraging from reproducing people who are more than 2 standard deviations taller than the rest of their country average or reference ethnicity) is already an ethically unacceptable form of eugenics, independently from its practical impact on the genetic variation of humanity.