Although the Talmud was unable to explain the scientific mechanisms of inheritance of traits, it was enlightened in assigning a role to the female "semen." Many scholars of that time believed that the female simply provided an incubator for the male seed to grow into a child. Even the Torah recognized the presence of a female seed with the passage: "If a woman emits a seed" (Leviticus 12:2).

Modern Concepts and Practice

Today, of course, we know of the genetic mechanisms of inheritance. There are many thousands of genes inherited by a child, which control the physical attributes of the child. For most traits a child inherits two copies of each gene, one from the mother and one from the father. The individual copies of each gene can interact with each other. A copy from one parent may be dominant over the other, and be preferentially expressed in the child. Or the two copies may work together to produce a combination or blended trait.

Assisted reproductive technology, which is available today, enables many infertile couples to fulfill the biblical commandment to "be fruitful and multiply." Technological advances have led to the development of In Vitro Fertilization, where the sperm from the father and the egg from the mother are mixed together in a petri dish in the laboratory, and the sperm is allowed to fertilize the egg, producing a "test-tube baby." The fertilized egg is then returned to the biological mother's womb where it develops, and nine months later the baby is born. In IVF, conception takes place outside of the body. This technique overcomes the problem of scarred, damaged, or blocked fallopian tubes (which prevent the sperm from reaching the eggs, and the eggs from reaching the uterus). It also allows men with low sperm counts to conceive, as sperm samples can be concentrated and deposited adjacent to the ripe eggs. Only small numbers of viable sperm are needed for successful fertilization in a petri dish.

A variation on this theme is Intra-Cytoplasmic Sperm Injection, or ICSI. With this technique a man who produces no sperm in his ejaculate can become a father. Pieces of tissue from the testicle can be used. Only a few sperm cells need to be isolated from the testis, and those cells can be mechanically injected, one by one, into individual eggs. Another variation involves a process called Assisted Hatching. In Assisted Hatching a small opening is made in the clear zone, or "shell" around the egg. The process is done to allow the fertilized egg to emerge properly, as this can assist it to implant into the lining of the uterus.

Implications In Jewish Law

How Kosher are these techniques in terms of halacha? It is generally agreed by rabbinic authorities that IVF and related techniques are acceptable for Jewish couples when the husband's sperm and the wife's eggs are used. In husband/wife IVF the problems, which need to be addressed, include the following:

(1) There is some controversy regarding how semen may be procured for the procedure. Since there is a biblical admonition regarding the "spilling of seed," some rabbis insist that the husband may not ejaculate to provide a specimen. However, since the intention of the procedure is specifically to enhance procreation and the semen is not being wasted, ejaculation to produce the semen may indeed be permissible.