Montgomery's team theorized that knocking out the pig gene for a carbohydrate that triggers rejection - a sugar molecule, or glycan, called alpha-gal - would prevent the problem.

What this means is that human and pig are very close. Humans and pigs share many traits not found in any other primates. That little seam in the center of your upper lip, where some kids are born with a cleft. Pigs have that junction and chimps don't. Another interesting trait is that aft limbs are longer than forelimbs in pigs, as legs are longer than arms in humans. Not so in primates.