Wednesday, November 14, 2007

Ya'akov and the Spotted Sheep

A few years ago, a rabbi from M'chon Pu'ah delivered a series of lectures to our s'micha class in Israel. The lectures were designed to give future rabbis insight into the complexities of fertility treatments and halachot which deal with reproduction. At the end of the first session, he told us a fascinating, novel approach he had regarding Ya'akov's spotted and striped sheep. While it may not be quite the pshat, it certainly is interesting.

In the story, Lavan gives Ya'akov only block colored animals. The striped, spotted and banded ones stay with Lavan's sons. Ya'akov puts striped branches within the sheeps' sight when they drink, and when they mate, they somehow give birth to striped animals. Of course, this seems non-sensical. I always understood the story as Ya'akov doing his best hishtadlut and Hashem lending a hand. But how?

When Ya'akov explains how he is so successful to his wives, he tells them of a vision he had when approached by an angel of God. "Behold, all the males that mated with the ewes, were striped, spotted and banded." How does Ya'akov's vision match the reality of the situation?

In genetics, there are dominant and recessive genes. In peas, to use one facet of Gregor Mendel's experiments, green peas are recessive, and yellow are dominant. The way genetics work is that a plant or animal inherits two sets of genes, one from each parent. As long as there is one dominant, the pea expresses a fully dominant phenotype, and will be yellow. Only when both inherited alleles are recessive will the phenotype be expressed as green.

It has been some time, but I hope that I accurately relate what Rabbi Brownstein explained: Striped and spotted sheep are the result of a recessive genetic mutation. The block colored ones are dominant. It so happens, he said, that the recessive gene also relates to earlier heat seasons.

When Ya'akov had a flock of block colored sheep, he had homozygous and heterozygous males and females. The sheep that were ready to mate earlier would likely carry a recessive gene for spotting and striping, heterozygously. Thus, the ewes ready for mating earlier, even though they were identical in phenotype to the homozygous sheep, were ones that could produce homozygous recessive babies, if mated with males that also carried the recessive gene.

This is the 'opening of the eyes' that the angel performed on Ya'akov. He allowed Ya'akov to 'see' the stripes that were latent in the block colored animals, and taught him that the only way to have a high number of striped offspring would be to allow heterozygotes to mate with heterozygotes. Allow the animals that were ready to mate early to mate together, and then segregate all striped and spotted offspring, permitting them only to reproduce amongst themselves, maintaining the homozygous recessive genes in his flocks.

All that is left are the branches in the watering troughs. It seems that in ancient times, this type of trick was believed to have worked. In fact, the Talmud records just such a popular belief in the idea that what one sees can influence the look of one's offspring (see Brachot and Niddah; exact pages forthcoming). Ya'akov's actions are nothing more than the use of the best animal husbandry knowledge of his time. It is a model for us of hishtadlut.