Think in scale. If you don't breed your cows, the neighbor's bull will come over the fence and do it for you, so you're incentivized to keep your cows bred. One bull will handle a large number of cows, so picking desirable bulls and a variety of interesting cows gives (roughly) $nCows potential picks for the next generation per herd (and Bakewell had many). Cows gestate for 8 months and results are frequently apparent in very young calves. Sexual maturity hits at 12-15 months (though, traditionally, first calf heifers were bred closer to 2 years), so 4 generations per decade in direct lineage isn't impossible.
It's not particularly difficult to select for specific traits when you consider inbreeding (which Bakewell did) and linebreeding (same idea, but avoiding excessive coefficient of inbreeding). Arguably, changing the muscle distribution on a domestic cow given a plethora of similar domestic breeds with different muscle distribution is easier than shrinking the adrenal gland in a wild fox given only wild stock.
Not to diminish in any way Bakewell's accomplishments. He revolutionized the field of animal husbandry.
Late edit to add an example: our (big, light brown, horned) Jersey milk cow came into heat and the (smaller, oreo-colored: almost black, white band around the belly, almost black; no horns) Belted Galloway bull jumped the fence, siring a heifer with small horns, a redder black, a splotchy band, and significantly greater size. Her offspring (against a bull from the same herd, possibly her sire) are medium-dark brown with a red tinge and a splotch of white, have no horns, and are still larger. Their offspring are very dark, solid brown with obvious red in sunlight, are still larger than the non-Jersey lines, and have, in every example, excellent conformation. All this in the last 7 years. The most recent generation will calf next year. Imagine what we could do with a targeted selection program!
It's not particularly difficult to select for specific traits when you consider inbreeding (which Bakewell did) and linebreeding (same idea, but avoiding excessive coefficient of inbreeding). Arguably, changing the muscle distribution on a domestic cow given a plethora of similar domestic breeds with different muscle distribution is easier than shrinking the adrenal gland in a wild fox given only wild stock.
Not to diminish in any way Bakewell's accomplishments. He revolutionized the field of animal husbandry.
Late edit to add an example: our (big, light brown, horned) Jersey milk cow came into heat and the (smaller, oreo-colored: almost black, white band around the belly, almost black; no horns) Belted Galloway bull jumped the fence, siring a heifer with small horns, a redder black, a splotchy band, and significantly greater size. Her offspring (against a bull from the same herd, possibly her sire) are medium-dark brown with a red tinge and a splotch of white, have no horns, and are still larger. Their offspring are very dark, solid brown with obvious red in sunlight, are still larger than the non-Jersey lines, and have, in every example, excellent conformation. All this in the last 7 years. The most recent generation will calf next year. Imagine what we could do with a targeted selection program!