Men Can't Hear: Sex-Linked Sensory Differences

July 20, 2009— -- When it comes to the difference between men and women, there may be no accounting for taste -- but you can account for smell.

Men's senses and women's senses are a combination of sense stimulation and the brain processing information. There are often pronounced differences in the ways men and women perceive smells, sounds, and sights. There are fewer differences between men's and women's senses of taste and touch, but in general, men underperform compared to women in the sensory department.

Men are more likely to suffer hearing loss, they have a less developed sense of smell, and the idea that they prefer the taste of beer more than women do is false.

"In general, women seem to have a slight edge up on men in terms of abilities," said Dr. Paul Breslin, a professor of Nutrition at Rutgers University and a member of the Monell Chemical Senses Center in Philadelphia.

Some of these differences evolved over time, allowing men and women to choose the best foods or select their optimal mate.

And some of these differences can still be physiological. Men don't experience the pronounced hormonal changes women do, during pregnancy for example, but their bodies change as they become older.

"All the senses decrease as you get older," Breslin said. "Olfaction takes a nosedive, you lose vision."

No one's senses are immune to the ravages of time.

The following is a list of some of the unique aspects of male senses.

Human color vision is based on three light sensing proteins, two of which have genes located on the X chromosome. For women, who have two copies of the X chromosome, if one of the genes does not function properly, there is a greater chance that the extra copy of the gene on the other chromosome can compensate.

But in men, one mutated gene is enough to significantly affect their vision, and the most common defect is red-green color blindness.

"This is a typical X-linked trait that is much more common in men than in women," said Dr. Jeremy Nathans, a professor of molecular biology and genetics at the Johns Hopkins University School of Medicine.

People with red-green color blindness have difficulty distinguishing colors at which light travels at longer wavelengths -- reds, oranges, yellows. People with one defective color vision gene -- known as dichromads -- make up approximately 2 percent of the caucasian male population, according to Nathans, while those with an altered color gene make up between 6 percent and 7 percent of the caucasian male population.

Nathans said color blindness in African and Asian populations is less common by half, but the reasons for this are not known.

While color blindness can be a burden as far as distinguishing colors at long wavelengths, Nathans said there are situations where the trait can be helpful.

"Dichromads do better at tasks where color acts as a distraction," he said, in situations where spotting camouflaged objects is important, for example.

According to a study from Johns Hopkins University, men are five and a half times more likely than women to experience hearing loss as they age, starting as young as 20 years old.

"Basically, men have overall worse hearing than women as they age, but it's hard to isolate behavioral risk factors," said Dr. Charles Limb, an associate professor in the Department of Otolaryngology-Head and Neck Surgery at Johns Hopkins University School of Medicine.

Differences in men's hearing ability versus women, however, is the result of environmental factors. When they are born, boys and girls exhibit equivalent hearing, meaning there is nothing that genetically predisposes men to have worse hearing than women.

Limb pointed out that risk factors like cardiovascular disease and smoking are more prevalent among men and could contribute to hearing loss, but that men are more likely to be in situations of high noise exposure -- working in construction, for example, or being in the military -- and less likely to use earplugs or protect themselves otherwise.

And the hearing problem doesn't resolve as men get older.

"Men are more likely to need hearing aids, but women are more likely to wear them," Limb said.

"Body odor is influenced by gender and sexual orientation," said Dr. Charles J. Wysocki, an olfactory expert at the Monell Chemical Senses Center. "Perception of body odor is also influenced by both of those factors."

Wysocki said studies have shown that heterosexual males, heterosexual females, lesbians and gay men have specific preferences for body odors from other people. Given the choice between heterosexual male body odor and gay male body odor, heterosexual men and women and lesbians prefer heterosexual male body odor, but gay men choose the gay male body odor.

But in general, men are less sensitive to the subtleties of body odor than women are. In another study to determine if certain scents could mask body odor for men or women, out of 40 different materials, one third were effective at masking male body odor from men while none were effective at masking male body odor from females. Out of 45 different materials, half were effective at masking female body odors from men while only two were effective at masking female body odor from female.

"For a biologically relevant [body odor], it is very difficult to reduce the impact of that odor in the nose of females," Wysocki said. "It is much easier to reduce the impact in the nose of males."

Wysocki said this may be because body odor is predictive of the underlying genes associated with the immune system and that females are more likely to be tuned to choose mates with immune systems that are as different as possible from their own because they have a more limited capacity to reproduce successfully in their lifespan.

"Males can reproduce daily," Wysocki said, and there is less evolutionary pressure on them to gain more information from potential mates.

Taste perception may be one of the most subjective of the five senses, but there are few biological differences between men and women.

There are times when a woman's sense of taste will become more sensitized to certain flavors -- during pregnancy, for example -- and there is no analogous change in taste for men at any point in life.

But overall, sense of taste tends to be consistent across gender as well as across age.

"Taste probably resists decaying with age the best of all the senses," Breslin said. "We know people can live just fine without vision or hearing. But if you can't taste, truly can't taste, it can be a real problem for people."

Taste buds and tongue tissue is highly resilient, regenerating itself constantly and resisting change over time, but Breslin pointed out that people can lose their sense of taste, through chemotherapy for head and neck cancer, for example, and they can have a difficult time eating and getting enough nutrition to sustain themselves.

"It's probably the one sense that, more than any other sense, would be difficult to live without."

Touch is a subset of our peripheral senses. Nerve cells transmit information to the spinal cord and brain where the sensation is interpreted. Some nerves are activated by intense, painful pressure, some are activated by light touch, some remain active for a long time, and some become sensitized to a stimulus quickly until it changes.

"Of all the mechanical senses, the two that are most likely to show some gender differences are in pain sensitivity ... and sensual touch, I would guess," said Dr. Mike Caterina, an associate professor of biological chemistry at the Johns Hopkins School of Medicine.

Ongoing research on low-threshold C-fibers, which are smaller and thinner than other neurons that perceive touch, have shown them to be involved in some of the sensual aspects of touch, Caterina said.

"They are involved in a lot of social interactions -- maternal-child bonding or sexual situations -- tactile information that is transmitted back and forth," Caterina said.

Further research might indicate greater differences between how males and females perceive touch from these low-threshold C-fibers.