many trees and shrubs in the Vatican garden. A complex network of cables hung over our heads, and large antennas betrayed an advanced communications system. The way back to the Middle Ages had been cut off. So that ended my chance to establish the truth of the chair and Pope Joan, but the matter continued to preoccupy me. If the chair didnât exist, why didnât the security officer just say so? Why did he keep stringing us along? Was the chair still being used, or might Pope Benedict XVI have been toying with the idea of reinstating this old custom?
4
Puberty, Love, and Sexual Behavior
THE ADOLESCENT BRAIN
Puberty starts with a kiss.
Dungan et al., 2006
In puberty, the pituitary gland starts to produce sex hormones. These affect the adolescent brain, causing marked and often incredibly annoying behavioral changes. The evolutionary advantage of puberty is clear: Youngsters are being prepared for reproduction. And their annoying behavior, leading to frequent clashes with their families, makes it less likely that reproduction will take place in their own surroundings, thus reducing the risk of inherited defects. The craving for new experiences, the readiness to take great risks, and the impulsive behavior are all part of preparations to leave the nest. Because their prefrontal cortex hasnât yet matured, adolescents can think only in the short term and are unable to take in the negative consequences of risky choices. As a result, they are also more likely to try addictive substances that can permanently damage the developing brain.
A great many chemical changes are needed to initiate puberty. Its onset is triggered by the gene KISS1, which produces the protein kisspeptins in the hypothalamus. The gene is so central to this process that it has been said that âpuberty starts with a kiss.â The gene was discovered by American researchers in Hershey, Pennsylvania, and named after the most famous local product, the Hershey Chocolate Kiss. People with a mutation in the KISS1 system never enter puberty.
However, puberty is dependent on other systems, too. For instance, women must have sufficient fat reserves to be able to nourish a fetus at times of scarcity. Before puberty, the brain registers whether thereâs sufficient fatty tissue by monitoring the amount of leptin, a hormone thatâs produced by fat cells. If the fat reserves are insufficientâbecause of an eating disorder, for instance, or intense athletic trainingâleptin levels decline and puberty is delayed, sometimes for good. Similarly, mutations in the leptin gene can impede puberty and also cause extreme obesity. In such cases, the brain registers the absence of leptinâand therefore of fat. The brain then blocks the onset of puberty because pregnancy would be too risky while also sending out a signal to eat copiously to make up fat reservesâunaware that itâs merely leptin, not fat, thatâs lacking.
Melatonin, a hormone produced by the pineal gland, is one of the substances that prevent the onset of puberty in children. Melatoninâs inhibiting effect has been known since 1898, when Otto Heubner described a boy of four and a half who had already entered puberty. He turned out to have a brain tumor that had destroyed his pineal gland, which resulted in a lack of melatonin, in turn spurring the onset of puberty. A Dutch girl who started puberty at the age of three and a half was more fortunate. She didnât have a brain tumor and was given inhibitory hormones up to the age of twelve. Then she entered puberty again and is now flourishing at secondary school. Conversely, some peopleâs melatonin level is too high and has to be normalized before puberty can start.
Puberty can also be disrupted by a condition known as Kallmann syndrome. Normally, the brain cells that stimulate the sex hormonesdevelop at the place where a fetusâs nose develops. The cells then migrate along the olfactory nerve to the
4
Puberty, Love, and Sexual Behavior
THE ADOLESCENT BRAIN
Puberty starts with a kiss.
Dungan et al., 2006
In puberty, the pituitary gland starts to produce sex hormones. These affect the adolescent brain, causing marked and often incredibly annoying behavioral changes. The evolutionary advantage of puberty is clear: Youngsters are being prepared for reproduction. And their annoying behavior, leading to frequent clashes with their families, makes it less likely that reproduction will take place in their own surroundings, thus reducing the risk of inherited defects. The craving for new experiences, the readiness to take great risks, and the impulsive behavior are all part of preparations to leave the nest. Because their prefrontal cortex hasnât yet matured, adolescents can think only in the short term and are unable to take in the negative consequences of risky choices. As a result, they are also more likely to try addictive substances that can permanently damage the developing brain.
A great many chemical changes are needed to initiate puberty. Its onset is triggered by the gene KISS1, which produces the protein kisspeptins in the hypothalamus. The gene is so central to this process that it has been said that âpuberty starts with a kiss.â The gene was discovered by American researchers in Hershey, Pennsylvania, and named after the most famous local product, the Hershey Chocolate Kiss. People with a mutation in the KISS1 system never enter puberty.
However, puberty is dependent on other systems, too. For instance, women must have sufficient fat reserves to be able to nourish a fetus at times of scarcity. Before puberty, the brain registers whether thereâs sufficient fatty tissue by monitoring the amount of leptin, a hormone thatâs produced by fat cells. If the fat reserves are insufficientâbecause of an eating disorder, for instance, or intense athletic trainingâleptin levels decline and puberty is delayed, sometimes for good. Similarly, mutations in the leptin gene can impede puberty and also cause extreme obesity. In such cases, the brain registers the absence of leptinâand therefore of fat. The brain then blocks the onset of puberty because pregnancy would be too risky while also sending out a signal to eat copiously to make up fat reservesâunaware that itâs merely leptin, not fat, thatâs lacking.
Melatonin, a hormone produced by the pineal gland, is one of the substances that prevent the onset of puberty in children. Melatoninâs inhibiting effect has been known since 1898, when Otto Heubner described a boy of four and a half who had already entered puberty. He turned out to have a brain tumor that had destroyed his pineal gland, which resulted in a lack of melatonin, in turn spurring the onset of puberty. A Dutch girl who started puberty at the age of three and a half was more fortunate. She didnât have a brain tumor and was given inhibitory hormones up to the age of twelve. Then she entered puberty again and is now flourishing at secondary school. Conversely, some peopleâs melatonin level is too high and has to be normalized before puberty can start.
Puberty can also be disrupted by a condition known as Kallmann syndrome. Normally, the brain cells that stimulate the sex hormonesdevelop at the place where a fetusâs nose develops. The cells then migrate along the olfactory nerve to the
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