Why did dogs
“evolve” faster
than us?

The full narration of the video.

People say dogs evolve incredibly fast. From wolf to Chihuahua in just over ten thousand years. And humans? We seem to have barely changed. That's only half right. Let's work backward from the result, one step at a time: where did all these shapes come from? Start with the result. The world's kennel clubs list more than three hundred breeds. The smallest Chihuahua weighs under three kilos; a big mastiff can top seventy.

Stranger still is the timing. Most of those breeds were fixed only in the last two hundred years. Two hundred years is only seven or eight human generations. So how did dogs change so much? Clue number one: dogs turn over generations fast. Humans become parents at around twenty-seven on average. A dog can have puppies at about one year old. In the same two hundred years: seven or eight human generations, dozens of dog generations.

But fast generations aren't enough. Mice breed even faster, and they never turned into three hundred different shapes. Clue number two is the key: in every generation, people choose who gets to have puppies. Want small dogs? Only let the two smallest mate. When the puppies arrive, pick the smallest again. Pick every generation, and they shrink a little every generation.

How fast can that go? Someone tested it. In 1959, Soviet scientists began breeding silver foxes. In each generation, only the least fearful few got to have pups. By the sixth generation, some pups were competing to be petted, wagging their tails and licking hands. Later, some had floppy ears and white patches in their fur. Clue number three: people didn't have to wait for something new to appear. The genetic switch that makes dogs small was already in a wolf from over fifty thousand years ago.

It's like a deck of cards: the cards you want are already in there. People just kept drawing out the ones they wanted, over and over. So dogs didn't evolve fast on their own; someone chose for them, every generation. Humans are evolving too. Nobody's choosing for us. Take milk. Most mammals can't digest it once they grow up. But where people drank a lot of milk, more and more could. Today about a third of adults worldwide still can.

That was chosen slowly by life itself, and took thousands of years to show. Dogs were chosen by hand, and it shows within decades. Dogs aren't the only ones. Broccoli, cabbage, cauliflower and kale were all picked out of the same wild cabbage. What else have you seen that people shaped, one generation at a time?