There seems to be something about steroid hormones that unavoidably depresses immune defense. This immune effect of testosterone is the reason that men are more susceptible to infectious diseases than women, a trend that occurs throughout the animal kingdom. Eunuchs live longer than other men, and male creatures generally suffer from higher mortality and strain. In a small Australian creature called the marsupial mouse, all the males contract fatal diseases during the frantic breeding season and die. It is as if male animals have a finite sum of energy that they can spend on testosterone or
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