Excerpt from Our Stolen Future’s Chapter, “Fifty Ways to Lose Your Fertility.”
Humans have long used marijuana as a drug because the chemicals it contains act in the brain to alter mood and perception, creating a “high.” But as Hughes and others discovered, these chemicals do more than induce a pleasant mellowness; they interfere with reproduction in a variety of ways. The same compound that makes a pot smoker high also acts on the testicles to reduce the synthesis of testosterone and on the brain to suppress lutenizing hormone, a key hormone that cues ovulation in females and testosterone production in males. Studies have reported that marijuana feminized men who smoked it heavily.
Hughes’s work focused on the way that marijuana interferes with the hormone prolactin, which is produced in the brain and signals the breast to produce milk. Mother rats given marijuana produced no milk, and their pups died of starvation. Hughes later moved on to investigate the effects of plant estrogens on the endocrine system and the hormones that orchestrate reproduction, an area few scientists had explored.
For such a defensive strategy to work, he explains, the plant would logically target females rather than males because a predator’s reproduction is limited. by the number of fertile females. If, for example, a plant managed to impair the fertility of all the males save one, that single male can, nevertheless, fertilize an entire flock of females. But if only a single female is fertile, she can produce only one or two lambs. Plants containing estrogen mimics produce them according to a seasonal pattern that fits perfectly with this strategy. Clover packs the greatest concentrations of estrogenic compounds into the new growth in spring, and when a rabbit or a sheep injures it by munching on these tender shoots, the plant responds by producing even more estrogen at the site of injury, delivering an added dose to predators that continue grazing.