In Genesis 30, Jacob's payment for his many years of service for Laban is given as all the spotted and speckled animals in Laban's flocks as well as a promise to get all future spotted and speckled animals born in the future.
Laban eagerly agrees knowing that those color markings are irregular and uncommon. So he separates the regular sheep and cattle from the spotted, streaked, and speckled ones and delivers them to Jacob's sons' three days away.
Now Jacob is still caring for Laban's flocks and, of course, he wants more sheep and cows, so what does he do?
37And Jacob took him rods of green poplar, and of the hazel and chesnut tree; and pilled white strakes in them, and made the white appear which was in the rods.
38And he set the rods which he had pilled before the flocks in the gutters in the watering troughs when the flocks came to drink, that they should conceive when they came to drink. 39And the flocks conceived before the rods, and brought forth cattle ringstraked, speckled, and spotted.
40And Jacob did separate the lambs, and set the faces of the flocks toward the ringstraked, and all the brown in the flock of Laban; and he put his own flocks by themselves, and put them not unto Laban's cattle.
41And it came to pass, whensoever the stronger cattle did conceive, that Jacob laid the rods before the eyes of the cattle in the gutters, that they might conceive among the rods.
42But when the cattle were feeble, he put them not in: so the feebler were Laban's, and the stronger Jacob's.
Jacob made spotted and speckled sticks and put them before the sheep and cattle. This excited the animals so much that they got into orgasmic rushes and immediately copulated and soon had spotted and speckled young.
Ok, what? Seeing spotted sticks makes animals have spotted young?
If you lived thousands of years ago and had never heard of genetics, I'm sure sympathetic magic wouldn't make you think twice either.