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Why haven't bald men gone extinct?
44 | NewScientist | 16 June 2012
Scott Schafer/Image Source/Gallerystock.com
Hirsute Pursuits If nature left us with something on top, how and why do so many men lose it, wonders Rob Dunn
S
OME of life’s greatest mysteries are hidden in full view. This one is particularly blatant. You will find it in almost every office, college, restaurant and public meeting place. It is a constant companion to 40 million men in the US and hundreds of millions more worldwide. In fact, I need look no further than my mirror to see a shining example. The bald male head is everywhere. For its owners the biggest puzzle is often how to get rid of it. Baldness is a key medical problem, in need of an immediate solution. Well, according to many of my fellow slapheads it is. Down the ages, the lengths to which some men have gone to acquire a flowing mane are almost as great as those to which they have gone to cure impotence. Until recently, however, our ability to find a remedy has been hampered by a rather sketchy understanding of precisely what it is that causes male pattern baldness in the first place. That looks set to change, as a flurry of activity in the lab shines a light on the makings of the bald pate. But even as we come to grasp why men lose
their hair, baldness remains an enigma. Surely, if the hair on our heads has its uses – protection from the sun, a little bit of warmth and also, perhaps, sexiness – men who lose theirs are at a disadvantage. Why then have the genes associated with male pattern baldness been successfully passed on, rather than becoming a little more rare with each generation? Why, in other words, haven’t bald men gone extinct? As an evolutionary biologist – and one who is actually perfectly happy with his smooth canopy – this is a puzzle I find particularly intriguing. By age 30 a quarter of men have started to lose their hair. Male pattern baldness has a predictable geography: the hair begins to disappear on the temples, then on the top of the head, before staging a general retreat. One of the first clues about the origins of this oft-distressing migration came from the observation by the ancient Greek philosopher Hippocrates that eunuchs never go bald. We now know that is because one trigger of baldness is the production of high levels of testosterone in and around the hair follicles –
those on the back of the head have fewer receptors for testosterone, making them less susceptible to the hormone’s effects. Testosterone is converted to dihydrotestosterone by the body and this somehow stops follicles producing individual hairs that are long and thick and instead triggers them to produce short, fine hairs similar to those that grow on babies’ heads. So, in essence, what is happening as hairlines recede is that men are regressing, their hair follicles becoming more juvenile as they age. An obvious conclusion here is that castration can prevent balding. While men have submitted to all sorts of whacky treatments for baldness (see “Hair-raising remedies”, p 46) this one has proved remarkably unpopular. But testosterone is only part of the story of baldness and, fortunately, recent advances in our understanding of the problem offer the prospect of more appealing solutions. Under normal circumstances, hair follicles undergo cycles of growth and quiescence. During growth cycles, stem cells in a region > 16 June 2012 | NewScientist | 45
”Even when the physiology of baldness is revealed in every detail, the central puzzle will still remain” process of becoming hair (Journal of Clinical Investigation, vol 121, p 613). It was a basic bit of knowledge and yet a big advance. Stem cells have the potential to become almost any cell type, and if we can figure out how to turn on the right genes to transform them into hair, there is hope for discontented bald men everywhere. This prospect appeared to have come a step closer last year when a team at
Berlin Technical University in Germany described growing hair in the lab from cells taken from human scalps (Journal of Biotechnology, vol 152, p 108). The transformation depended on a complex cacophony of many compounds, and orchestrating these in the wilds of the human head will be far more difficult than doing it in a Petri dish. Nevertheless, excitement is building around the potential this breakthrough offers for making hairless heads hirsute once again. But why are my stem cells, and those of other bald men, failing to become progenitor cells in the first place? A group led by Valerie Horsely at Yale University has discovered part of the answer. They found that, in mice at least, the signals required to turn stem cells into progenitor cells come from fat adjacent to the follicle. The layer of fat on the scalps of bald men – and bald mice – has long been known to be thinner than it is on non-bald men, even if their fat layers elsewhere are not (Cell, vol 146, p 761). Another clue comes from Cotsarelis’s latest research. He found that a chemical, a prostaglandin called D2, represses the activation of stem cells. Concentrations of D2 tend to be higher in the bald parts of men’s heads compared with the hairy parts (Science Translational Medicine, vol 4, p 126ra34). So it looks like baldness is caused both by the absence of signals that stimulate the stem cells and by the presence of signals that tell them to remain inactive. Double whammy.
ITV/Rex Features
at the base of the follicle called the bulge, become larger, more active hair progenitor cells, which then divide rapidly to initiate the growth of a new hair shaft (see diagram, p 47). Assuming there must be something amiss here in balding men, George Cotsarelis at the University of Pennsylvania, Philadelphia, and colleagues scrutinised hair follicles on the bald and non-bald parts of their heads. The team expected to find that both the stem cells and the progenitor cells were missing where hair was thinning. They were in for a surprise. Although progenitor cells were almost non-existent in bald areas, the stem cells were thriving. The problem, it would appear, is that they are not being activated to start the
hair-raising remedies Among basic human requirements appear to be the need for food, water, sleep, shelter and a full head of hair. As early as 5000 years ago, wigs became popular among Assyrians, Sumerians, Persians and Greeks, as did herbal remedies for baldness. The ancient Egyptians recorded one of the oldest known treatments on the Ebers Papyrus, 3500 years ago. It consisted of a potion – a mixture of iron oxide, lead, onions, alabaster, honey, and the fat of a snake, crocodile, hippopotamus and lion – together with an incantation to the Sun god. Since then, anti-baldness advice has spanned the full range of embarrassing possibilities. Sleep on
46 | NewScientist | 16 June 2012
a tilted bed. Don’t masturbate. Grow your hair long. Don’t grow it long. Rub your head with red pepper, kerosene and carbolic acid. Slime with sage oil. Massage with a “Blud-Rub” machine. Wear a vacuum cap. Apply an electric comb. Have hot wax injected under your scalp. Pour cold tea on your pate. Rub your head with lemon juice and dance under a full moon. Pray. Today, a hair transplant is a more popular option. This usually entails having strips of hair or individual hair follicles cut from a hairier part of your head – or from someone else’s – and grafted onto the bald region. Transplants of artificial hair are now possible too. It may sound extreme, but this is a multibillion dollar a year
business, so the odds are high that someone you work with or walk past every day has invested in it. A less drastic alternative is Propecia, a tablet made by Merck, which acts as a kind of localised biochemical castration, reducing the hair-depleting effects of excess testosterone. It works by limiting the effectiveness of the enzyme that converts testosterone into the offending dihydrotestosterone. Men who are losing their hair tend to have more of this enzyme, so Propecia makes them more average. Another popular treatment, minoxidil (marketed under the brand name Rogaine, among others), stimulates blood flow and appears to activate
enzymes that produce chemicals called prostaglandins, some of which promote hair growth. Via magic not yet understood, minoxidil can trigger additional growth of baby-fine hair, though typically not the sort of hair that has been lost. Recent insights into the biology of balding offer the promise of new treatments. In particular, a wide variety of products not quite yet on the market aim to stimulate the stem cells near hair follicles, which are inactive in bald men (see main article). Some scientists are even daring to talk about “the end of baldness”. We live in a brave new world where truly anything might be cured, even hair loss.
In good company: Julius Caesar is said to have invented the comb-over
variants. But think about it carefully and the logic fails – mothers are just as likely to have sons as daughters and every time they do, if these males are less likely to procreate, these variants should become rarer. In any case, science has shown that this mother-based hypothesis is wrong. We now know that a tendency to baldness can be inherited from both parents, though it is not clear what genetic variants are involved. What is safe to say, is that multiple genes influence the probability that a son will one day have to perform a comb-over (Australasian Journal of Dermatology, vol 745, p 81).
How to get ahead
No lives were saved in any of this research and yet to millions of baby-haired men, it is significant. Now we have some answers to the question of why men go bald, it looks like the business of alleviating baldness may finally succumb to science. Money and patents are flying fast and furious. Indeed, this area of research is so hot right now that the story will probably have moved on a great deal in as little as six months to a year. However, even when the physiology of baldness is revealed in every detail, the central puzzle will still remain. The intriguing question, the one likely to lead to more mysteries than a simple resolution, is why bald men exist in the first place. Baldness is extremely rare in nature. It remains unclear why, and when, our ancestors lost most of their fur (New Scientist, 24 March 2012, p 34) but there is general agreement that the few hairy bits we retained serve particular purposes. The hair on our heads may protect us from the noonday sun, maintain body heat when it is cold, and even attract a mate. If so, men who lose their hair are at a disadvantage, and you would expect natural and sexual selection to have weeded them out. So why haven’t bald men like me, or at least our versions of genes, gone extinct? One early stab at answering this question rested on the idea that a man’s genetic predisposition to baldness is found in genes he inherited from his mother. Since she would not have suffered baldness and its concomitant ill effects, natural selection would have no cause to remove these genetic
Perhaps, then, baldness has some survival advantage in human males, which allowed it to evolve. One suggestion is that it signals dominance and status. A bald pate might serve as a sort of advertising board for emotions, in particular the red flush that accompanies anger. In nature, red is often the colour of dominance, making an angry bald head the equivalent of a wordless but very clear statement of “Don’t mess with me!” But dominant individuals do not necessarily
Hair today, gone tomorrow Normal hair growth is triggered by stem cells in the bulge, but bald men lack the signals needed to activate them
HAIR
SEBACEOUS GLAND
ROOT SHEATH HAIR SHAFT
BULGE
ARRECTOR PILI MUSCLE
seem to lack hair. Many historically significant leaders across a range of cultures had lots of it. What’s more, we tend to discriminate against leaders who are short on hair. For example, elected officials in the US are less likely to be bald than men of the same age in the general public (Journal of Nonverbal Behavior, vol 4, p 269). Meanwhile, at least some of those leaders that were bald have hidden their “leadership signal” – Julius Caesar, for example, is said to have invented the comb-over. Another idea is that baldness might have evolved as a social signal of maturity, wisdom and nurturance. In the only study of this idea to date, bald men tended to be viewed by women as more mature and less aggressive, but also older and, I regret to say, less attractive (Ethology and Sociobiology, vol 17, p 99). The evolutionary question is why genes that helped to convey such a signal would be favoured. Given that the chance of going bald increases as men age, perhaps bald men do have fewer children but those they produce before losing their hair are more likely to prosper as a result of their father’s wisdom and nurturance. Or perhaps not. What if baldness is not a signal, but instead a physiological adaptation? Then one might expect its benefits to be useful in age but not in youth. A recent paper suggests baldness allows more sun to penetrate through the skulls of ageing men. This increases the generation of vitamin D and helps to forestall prostate cancer (Medical Hypotheses, vol 70, p 1038). That’s interesting, but even the simple next step of comparing prostate cancer in bald and hairy men has not been taken. Then again, male pattern baldness might not be adaptive. It could be due to genetic drift – the capriciousness by which some genes flourish by chance. Or maybe baldness is not adaptive itself but is instead genetically linked with some attribute of our ageing bodies that is adaptive. The genes that make men bald might also give them super powers of some yet-to-be-noticed variety. A guy can hope. If we could unambiguously identify some of the genes responsible for baldness we could test whether these had been favoured over recent evolutionary time. In the meantime, my shining forehead and those of millions of other men are left unexplained. Remember that the next time you think about making fun of a bald guy. We are mysterious. We gleam with an inexplicable magic – that and sweat. n Rob Dunn of North Carolina State University at Raleigh is author of The Wild Life of Our Bodies (Harper Collins, 2011) 16 June 2012 | NewScientist | 47
Scott Schafer/Image Source/Gallerystock.com
Hirsute Pursuits If nature left us with something on top, how and why do so many men lose it, wonders Rob Dunn
S
OME of life’s greatest mysteries are hidden in full view. This one is particularly blatant. You will find it in almost every office, college, restaurant and public meeting place. It is a constant companion to 40 million men in the US and hundreds of millions more worldwide. In fact, I need look no further than my mirror to see a shining example. The bald male head is everywhere. For its owners the biggest puzzle is often how to get rid of it. Baldness is a key medical problem, in need of an immediate solution. Well, according to many of my fellow slapheads it is. Down the ages, the lengths to which some men have gone to acquire a flowing mane are almost as great as those to which they have gone to cure impotence. Until recently, however, our ability to find a remedy has been hampered by a rather sketchy understanding of precisely what it is that causes male pattern baldness in the first place. That looks set to change, as a flurry of activity in the lab shines a light on the makings of the bald pate. But even as we come to grasp why men lose
their hair, baldness remains an enigma. Surely, if the hair on our heads has its uses – protection from the sun, a little bit of warmth and also, perhaps, sexiness – men who lose theirs are at a disadvantage. Why then have the genes associated with male pattern baldness been successfully passed on, rather than becoming a little more rare with each generation? Why, in other words, haven’t bald men gone extinct? As an evolutionary biologist – and one who is actually perfectly happy with his smooth canopy – this is a puzzle I find particularly intriguing. By age 30 a quarter of men have started to lose their hair. Male pattern baldness has a predictable geography: the hair begins to disappear on the temples, then on the top of the head, before staging a general retreat. One of the first clues about the origins of this oft-distressing migration came from the observation by the ancient Greek philosopher Hippocrates that eunuchs never go bald. We now know that is because one trigger of baldness is the production of high levels of testosterone in and around the hair follicles –
those on the back of the head have fewer receptors for testosterone, making them less susceptible to the hormone’s effects. Testosterone is converted to dihydrotestosterone by the body and this somehow stops follicles producing individual hairs that are long and thick and instead triggers them to produce short, fine hairs similar to those that grow on babies’ heads. So, in essence, what is happening as hairlines recede is that men are regressing, their hair follicles becoming more juvenile as they age. An obvious conclusion here is that castration can prevent balding. While men have submitted to all sorts of whacky treatments for baldness (see “Hair-raising remedies”, p 46) this one has proved remarkably unpopular. But testosterone is only part of the story of baldness and, fortunately, recent advances in our understanding of the problem offer the prospect of more appealing solutions. Under normal circumstances, hair follicles undergo cycles of growth and quiescence. During growth cycles, stem cells in a region > 16 June 2012 | NewScientist | 45
”Even when the physiology of baldness is revealed in every detail, the central puzzle will still remain” process of becoming hair (Journal of Clinical Investigation, vol 121, p 613). It was a basic bit of knowledge and yet a big advance. Stem cells have the potential to become almost any cell type, and if we can figure out how to turn on the right genes to transform them into hair, there is hope for discontented bald men everywhere. This prospect appeared to have come a step closer last year when a team at
Berlin Technical University in Germany described growing hair in the lab from cells taken from human scalps (Journal of Biotechnology, vol 152, p 108). The transformation depended on a complex cacophony of many compounds, and orchestrating these in the wilds of the human head will be far more difficult than doing it in a Petri dish. Nevertheless, excitement is building around the potential this breakthrough offers for making hairless heads hirsute once again. But why are my stem cells, and those of other bald men, failing to become progenitor cells in the first place? A group led by Valerie Horsely at Yale University has discovered part of the answer. They found that, in mice at least, the signals required to turn stem cells into progenitor cells come from fat adjacent to the follicle. The layer of fat on the scalps of bald men – and bald mice – has long been known to be thinner than it is on non-bald men, even if their fat layers elsewhere are not (Cell, vol 146, p 761). Another clue comes from Cotsarelis’s latest research. He found that a chemical, a prostaglandin called D2, represses the activation of stem cells. Concentrations of D2 tend to be higher in the bald parts of men’s heads compared with the hairy parts (Science Translational Medicine, vol 4, p 126ra34). So it looks like baldness is caused both by the absence of signals that stimulate the stem cells and by the presence of signals that tell them to remain inactive. Double whammy.
ITV/Rex Features
at the base of the follicle called the bulge, become larger, more active hair progenitor cells, which then divide rapidly to initiate the growth of a new hair shaft (see diagram, p 47). Assuming there must be something amiss here in balding men, George Cotsarelis at the University of Pennsylvania, Philadelphia, and colleagues scrutinised hair follicles on the bald and non-bald parts of their heads. The team expected to find that both the stem cells and the progenitor cells were missing where hair was thinning. They were in for a surprise. Although progenitor cells were almost non-existent in bald areas, the stem cells were thriving. The problem, it would appear, is that they are not being activated to start the
hair-raising remedies Among basic human requirements appear to be the need for food, water, sleep, shelter and a full head of hair. As early as 5000 years ago, wigs became popular among Assyrians, Sumerians, Persians and Greeks, as did herbal remedies for baldness. The ancient Egyptians recorded one of the oldest known treatments on the Ebers Papyrus, 3500 years ago. It consisted of a potion – a mixture of iron oxide, lead, onions, alabaster, honey, and the fat of a snake, crocodile, hippopotamus and lion – together with an incantation to the Sun god. Since then, anti-baldness advice has spanned the full range of embarrassing possibilities. Sleep on
46 | NewScientist | 16 June 2012
a tilted bed. Don’t masturbate. Grow your hair long. Don’t grow it long. Rub your head with red pepper, kerosene and carbolic acid. Slime with sage oil. Massage with a “Blud-Rub” machine. Wear a vacuum cap. Apply an electric comb. Have hot wax injected under your scalp. Pour cold tea on your pate. Rub your head with lemon juice and dance under a full moon. Pray. Today, a hair transplant is a more popular option. This usually entails having strips of hair or individual hair follicles cut from a hairier part of your head – or from someone else’s – and grafted onto the bald region. Transplants of artificial hair are now possible too. It may sound extreme, but this is a multibillion dollar a year
business, so the odds are high that someone you work with or walk past every day has invested in it. A less drastic alternative is Propecia, a tablet made by Merck, which acts as a kind of localised biochemical castration, reducing the hair-depleting effects of excess testosterone. It works by limiting the effectiveness of the enzyme that converts testosterone into the offending dihydrotestosterone. Men who are losing their hair tend to have more of this enzyme, so Propecia makes them more average. Another popular treatment, minoxidil (marketed under the brand name Rogaine, among others), stimulates blood flow and appears to activate
enzymes that produce chemicals called prostaglandins, some of which promote hair growth. Via magic not yet understood, minoxidil can trigger additional growth of baby-fine hair, though typically not the sort of hair that has been lost. Recent insights into the biology of balding offer the promise of new treatments. In particular, a wide variety of products not quite yet on the market aim to stimulate the stem cells near hair follicles, which are inactive in bald men (see main article). Some scientists are even daring to talk about “the end of baldness”. We live in a brave new world where truly anything might be cured, even hair loss.
In good company: Julius Caesar is said to have invented the comb-over
variants. But think about it carefully and the logic fails – mothers are just as likely to have sons as daughters and every time they do, if these males are less likely to procreate, these variants should become rarer. In any case, science has shown that this mother-based hypothesis is wrong. We now know that a tendency to baldness can be inherited from both parents, though it is not clear what genetic variants are involved. What is safe to say, is that multiple genes influence the probability that a son will one day have to perform a comb-over (Australasian Journal of Dermatology, vol 745, p 81).
How to get ahead
No lives were saved in any of this research and yet to millions of baby-haired men, it is significant. Now we have some answers to the question of why men go bald, it looks like the business of alleviating baldness may finally succumb to science. Money and patents are flying fast and furious. Indeed, this area of research is so hot right now that the story will probably have moved on a great deal in as little as six months to a year. However, even when the physiology of baldness is revealed in every detail, the central puzzle will still remain. The intriguing question, the one likely to lead to more mysteries than a simple resolution, is why bald men exist in the first place. Baldness is extremely rare in nature. It remains unclear why, and when, our ancestors lost most of their fur (New Scientist, 24 March 2012, p 34) but there is general agreement that the few hairy bits we retained serve particular purposes. The hair on our heads may protect us from the noonday sun, maintain body heat when it is cold, and even attract a mate. If so, men who lose their hair are at a disadvantage, and you would expect natural and sexual selection to have weeded them out. So why haven’t bald men like me, or at least our versions of genes, gone extinct? One early stab at answering this question rested on the idea that a man’s genetic predisposition to baldness is found in genes he inherited from his mother. Since she would not have suffered baldness and its concomitant ill effects, natural selection would have no cause to remove these genetic
Perhaps, then, baldness has some survival advantage in human males, which allowed it to evolve. One suggestion is that it signals dominance and status. A bald pate might serve as a sort of advertising board for emotions, in particular the red flush that accompanies anger. In nature, red is often the colour of dominance, making an angry bald head the equivalent of a wordless but very clear statement of “Don’t mess with me!” But dominant individuals do not necessarily
Hair today, gone tomorrow Normal hair growth is triggered by stem cells in the bulge, but bald men lack the signals needed to activate them
HAIR
SEBACEOUS GLAND
ROOT SHEATH HAIR SHAFT
BULGE
ARRECTOR PILI MUSCLE
seem to lack hair. Many historically significant leaders across a range of cultures had lots of it. What’s more, we tend to discriminate against leaders who are short on hair. For example, elected officials in the US are less likely to be bald than men of the same age in the general public (Journal of Nonverbal Behavior, vol 4, p 269). Meanwhile, at least some of those leaders that were bald have hidden their “leadership signal” – Julius Caesar, for example, is said to have invented the comb-over. Another idea is that baldness might have evolved as a social signal of maturity, wisdom and nurturance. In the only study of this idea to date, bald men tended to be viewed by women as more mature and less aggressive, but also older and, I regret to say, less attractive (Ethology and Sociobiology, vol 17, p 99). The evolutionary question is why genes that helped to convey such a signal would be favoured. Given that the chance of going bald increases as men age, perhaps bald men do have fewer children but those they produce before losing their hair are more likely to prosper as a result of their father’s wisdom and nurturance. Or perhaps not. What if baldness is not a signal, but instead a physiological adaptation? Then one might expect its benefits to be useful in age but not in youth. A recent paper suggests baldness allows more sun to penetrate through the skulls of ageing men. This increases the generation of vitamin D and helps to forestall prostate cancer (Medical Hypotheses, vol 70, p 1038). That’s interesting, but even the simple next step of comparing prostate cancer in bald and hairy men has not been taken. Then again, male pattern baldness might not be adaptive. It could be due to genetic drift – the capriciousness by which some genes flourish by chance. Or maybe baldness is not adaptive itself but is instead genetically linked with some attribute of our ageing bodies that is adaptive. The genes that make men bald might also give them super powers of some yet-to-be-noticed variety. A guy can hope. If we could unambiguously identify some of the genes responsible for baldness we could test whether these had been favoured over recent evolutionary time. In the meantime, my shining forehead and those of millions of other men are left unexplained. Remember that the next time you think about making fun of a bald guy. We are mysterious. We gleam with an inexplicable magic – that and sweat. n Rob Dunn of North Carolina State University at Raleigh is author of The Wild Life of Our Bodies (Harper Collins, 2011) 16 June 2012 | NewScientist | 47