Ever noticed how dogs can be so different?  Yet they are all still part of the same Canis Lupus Familiaris species.  According to that Wikipedia link, there are over 400 million dogs in the world, ranging from the 15cm Chihuahua to the 75cm Irish Wolfhound.  And in between, dogs range from the curly Poodles to the mop-like Cocker Spaniels, and from the fuzzy Chow Chow to the dog that looks like it ran into a wall (pug).

Imagine a world where human races differ as much in physical attributes as dogs do.  One race might have super long hair.  Another might have really short legs and a long body.  Another might have super sharp ears.  Would our world be any different?

Perhaps we would optimize.  The tall people will have jobs like window cleaning or painting.  The hairy people will have jobs in cold places.  Perhaps we would rejoice in our differences.  Whenever we saw someone who looked different than us, we would bound up to them in excitement and examine their bodies.  We would run and play with each other regardless of how fast we ran or how funny we looked.  Or perhaps we would discriminate.  The stronger dogs would take all the frisbees and the Cocker Spaniels would be sent to sweep the streets.

The thing is, only 7 genes determine about 80% of differences in dog appearances.  They’re not so different after all.  If dogs who appear so different can overcome their 20% difference, why is it that animals with 0.1% difference have such a hard time?