Question: would it be possible to breed a unicorn?

Steven Gardner answered on 17 Jun 2013:

I think the answer is yes, though it might take a long time!

It’s possible to artificially change a plant or animal over time by a process called selective breeding. This is where you pick animals that have the thing you want and only let them breed. The children of these animals are then morelikely to inherit these traits from their parents. You then pick the children of these animals who have the best of whatever it is your want (in this case the biggest horn) and only let them breed with each other (so long as they are not in the same family). If you do this over many generations it might be possible to make a unicorn. Nature does this already by a process known as evolution by natural selection. Giraffes have long necks because the ancestors of the giraffe had a slightly longer neck than then others, this gave it an advantage because it was able to reach higher food. When this was passed on, the children of the longer necked animal were more likely to survive through times of low food. They then passed on the long-neck gene to their children and so on, until you end up with a whole new animal that all have long necks.

Selective breeding is the same thing except it is humans that are deciding what should be passed on and not nature. Selective breeding is why horses have developed stronger spines so we could ride them, and why dairy cows produce more milk than they would ever need, and why carrots are orange. We selected all those things and only allowed the best examples to breed and pass the trait on.

So yeah, no reason why you couldn’t find a few horses with a tiny bump on their heads and breed them until they had full horns. I mean if we can make carrots orange why not?! It would take many generations though, and given that horses live for 20-30 years it might take longer time than you had.