The mechanics underlying Jacob's scheme have long perplexed Biblical commentators. On first glance, it seems to involve the ancient belief that sensory impressions at the moment of conception affect the embryo.

The peeled rods, with their stripes of white against dark bark, would impart the traits of spots or brindle markings upon the offspring. A similar effect would occur for the sheep by making them face Laban's1 flocks of speckled goats during their mating time.

Yehuda Feliks, an expert on biblical plants and animals, proposed the theory that the peeled rods are a merely a superficial gesture—a way to pay lip-service to folk-medicine tradition—and that what's really being described here are sound principles of animal husbandry: Jacob is careful to encourage the breeding only of the more vigorous animals, which, according to Feliks, would be more likely to be heterozygotes—bearing recessive genes such as black wool. Heterozygous animals tend to be stronger and more resistant to disease through a mechanism called “hybrid vigor.”

Using a Mendelian table, Feliks shows that recessive traits would have shown up in 25% of animals born in the first season, 12.5% born in the second season, and 6.25% in the third season. Thus Jacob's prioritization of potentially heterozygous offspring would have countered that natural decline. Ancient breeders, of course, had no knowledge of the underlying genetics, but that doesn't mean they were completely ignorant of the phenotypical patterns that emerged during tens of thousands of years of domestication (after all, they made edible almonds long before Mendel!)

This is only one interpretation, but it's worth pointing out that in the next chapter, Jacob makes no mention of the rods when he tells his wives how he acquired the flocks!

When Jacob asked Laban for wages he used a plan to get more flocks. The Bible,

37Jacob, however, took fresh-cut branches from poplar, almond and plane trees and made white stripes on them by peeling the bark and exposing the white inner wood of the branches. 38Then he placed the peeled branches in all the watering troughs, so that they would be directly in front of the flocks when they came to drink. When the flocks were in heat and came to drink, 39they mated in front of the branches. And they bore young that were streaked or speckled or spotted. 40Jacob set apart the young of the flock by themselves, but made the rest face the streaked and dark-colored animals that belonged to Laban. Thus he made separate flocks for himself and did not put them with Laban’s animals. 41Whenever the stronger females were in heat, Jacob would place the branches in the troughs in front of the animals so they would mate near the branches, 42but if the animals were weak, he would not place them there. So the weak animals went to Laban and the strong ones to Jacob. 43In this way the man grew exceedingly prosperous and came to own large flocks, and female and male servants, and camels and donkeys.

I've read this passage several times but still could not understand it well. What do you think about this? Thanks!