We think of genetics as a science now, not a mystery.
Plato thought that the "soul" "entered" the body at birth, which was all the Greeks knew of inheritance, and reproduction.
We now know that inheritance and all characteristics are passed through DNA, in random combinations, which include mutations that subtly alter the progression of the inherited blueprint.
We acquired these two younger Siamese cats from the same breeder. They were sisters, born of the same litter, of the same parents.
And yet, you'd never know it from looking at them today. As kittens, they looked much more alike. Both were lightly darkened at their points, and snow white otherwise. But in pretty short order, they diverged.
Lily Sabine (below) is slightly warm cream color with light grey points.
Cappucine (below) developed into a classic chocolate point. Cappy (for short) is a bit larger, while Sabine will always be a miniature. Cappy is stronger, and more determined, though less social than Sabine.
They have different voices. Sabine's is a delicate "mew" while Cappy generally has a vibra-tone, like a cackle. Both are very friendly, and will tolerate being held, but not for very long. Neither is a lap kitty, though Cappy will often settle on your legs in bed. Cappy is an aggressive hunter and chaser, while Sabine is gentler, and perhaps less wild.
Neither has been fixed, but that's not a problem since our male has been, and none of our cats goes outdoors.
They're still young, though full grown now. It will be interesting to see if we outlive this latest generation of our family pets, or they us.