1/10/2006: Cyclops kitten born

[Happy Monkey]

Originally Posted by mrnoodle

If you cut off the tails of 100 generations of 100 lines of the same breed of dog, wouldn't they eventually start evolving shorter tails? I thought that was one of the basic tenets of evolutionary science -- that the environment can make us change over time. Like back when we were apes, we started standing upright to see over the tall grass, and it stuck.

I'm really not joking.

No matter how many generations of women get their ears pierced, they won't be born with the holes. For evolution to happen, the change has to be in the DNA, and DNA isn't affected by injuries (radiation excepted, not that radiation effects are predictable). Evolution happens if a dog happens to have a short tail, and that somehow lets it have more babies. The next generation of dogs would then have a slightly larger percentage of short-tail dogs in its population, who would have a few more babies than average, further increasing the percentage of short-tail dogs in the next generation population. Eventually, they are the vast majority, and the species has evolved.

Here's a thought experiment relating to your example - Let's assume a predator that loves dog tail. If it sees a pack of dogs, it tries to bite off a tail. If it succeeds, that dog has a chance of getting an infection and dieing. Therefore, dogs with long tails attract more attacks, and have a correspondingly high death rate. Short tails are hard to get a hold on, so they fare better, and a mutant dog with no tail will escape unscathed.

But in a clinical trial, if you snip off the tails of some dogs, and then make sure each one survives the procedure and has the same number of babies, those babies will have roughly the same range of tail sizes as the parent generation, no matter how many generations you continue the experiment for.