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Mammalian sperm must reside in the female reproductive tract before they are able to undergo the acrosome reaction. This maturation process is called capacitation. The mammalian egg is surrounded by an extracellular envelope called the zona pellucida, to which sperm must bind and penetrate before they can make contact with the surface of the egg itself. The zona pellucida of the mouse egg contains three glycoproteins called ZP-1, ZP-2 and ZP-3 that polymerize to form a gel. The zona of newly-ovulated eggs is also surrounded by a constellation of follicle cells in a matrix of hyaluronic acid. Figure 1 shows...

... David Boonin, though not responding to George, also discounts the pro-lifer’s claim that the newly conceived embryo is a distinct, living, and whole human organism. How can this be, he argues, when we don’t know the precise moment during the conception process at which the new zygotic human being comes into existence? Here Boonin is both right and wrong. True, we don’t know exactly when during the conception process that the zygote comes to be. Some embryologists argue that it happens when the sperm penetrates the ovum while others point to syngamy, when the maternal and parental chromosomes crossover...

...The book begins with a discussion of the medical use of embryonic tissue and the debate over whether a blastocyst (which is a ball of a few hundred cells) is a person. This section is thoughtful, clearheaded and informed by developmental neuroscience. One fallacy Gazzaniga exposes depends on the common idea that graded differences block principled legal distinctions. In the version referred to as the fallacy of the beard, the logic goes like this: If we cannot say how long a man's whiskers must be to qualify as a beard, we cannot distinguish between a bearded man and a clean-shaven...