Why We Are Here: Continuous Facial and Cranial Hair Growth

[YuriZhivago]

Okay, so my science background is in engineering, not biology, and my physician ex-wife could never answer this question. That question being the fundamental reason we're all participants in this forum. Hopefully, there might be some biologists, anthropologists or geneticists, or some really insightful people participating here. The question is:

Of all the mammals, especially primates, who have hair coats that grow to a fixed length and then progressively shed, (excluding some dog breeds which were created by man), why does man have facial and cranial hair that grows without apparent limitation? What is the evolutionary purpose of such unlimited facial and cranial hair growth in humans?

In the evolution picture, this would seem to be counterproductive and require man to absolutely take a positive action to cut the hair at some point before it became a liability to eating, walking, sanitation, survival, etc. We most certainly lack the ability to groom without some type of tool as our hands and mouths are really limited for such grooming as compared to most mammals. Certainly the other types of hair on our bodies grow to an essentially fixed length and then stop, e.g. leg hair, chest hair, etc. However, there are Sikhs who have beards and cranial hair that range to about 8 or 9 feet in length and continue to grow unabated. The history of shaving dates back, I believe, some 30,000 years or so as archeologists have so far discovered some flint and obsidian tools.

Could evolution or adaptation and our ability to think and cut our facial and cranial hair, exposing our skin to the environment, have lead to the human genome being altered to permit such unrestricted hair growth?

[jamesspo]

Well, the wikipedia article on human hair growth says that all hair goes through the shedding cycle, but that it can grow longer by being in the Anagen (growth) phase for a longer period of time. We certainly do shed hairs, at least to a certain degree, so I imagine that the length of time spent in that phase probably varies from person to person..and thus some able to grow hair indefinately, and others have a fixed length that the hair will converge to over time.

http://en.wikipedia.org/wiki/Human_hair_growth

So as to how we ended up with having a long Anagen cycle for some hair types (scalp..maybe beard?) is something we'll need to research to understand. Maybe some others know why this is the case, but I'll see what I can dig up.

On the question of evolving to a longer cycle *because* of shaving (and its benefit to avoiding issues with long hair), I hesitate. 30,000 years is not a super long time in the evolutionary sense. That said, there has been quite a bit of controversy in this area recently about how fast evolution can actually occur, with some evidence that significant changes can occur with relatively few generations. I don't recall all of the factors that can accelerate the selection process (I'm an engineer as well)..another thing I'd need to go look at more deeply.

Ah, another quote from that article:

"In most people, scalp hair growth will halt due to follicle devitalization after reaching a length of generally two or three feet. Exceptions to this rule can be observed in individuals with hair development abnormalities, which may cause an unusual length of hair growth." [11]

[Foyle]

The answer is quite simple; God created us this way.

[Commander Quan]

I hesitate. 30,000 years is not a super long time in the evolutionary sense. That said, there has been quite a bit of controversy in this area recently about how fast evolution can actually occur, with some evidence that significant changes can occur with relatively few generations.

Any changes in the span of a few generations would fall into an adaptation as opposed to an evolution. For evolution to happen there needs to be significant changes in the human blueprint though genetics.

If I were to take a stab at guessing why we have hair growth the way we do, it would be because our ancestors found hair on the head and face to be a favorable trait for reproduction. Full hair is a sign of health, where as patchy or thin hair could be seen as a sign of illness or week genetics. Full hair may have also played a role in the staying power of human pheromones, so that the chemicals were not defused to quickly. Because of these favorable traits the humans with the stronger (hairier) genetics got to reproduce the most often.

[moto_mike]

The answer is quite simple; God created us this way.

I respectfully disagree.

I'm not a biologist, however, I am a scientist. A geologist to be more specific.

James makes some great points. I would like to throw past climate into the ring. We lost a lot of hair coming out of the last ice age. What's left may be simply a reaction to the climate of the different regions of the world where people reside and the way our genome responded to our environment. Obviously, not every single person of a particular region has the same hair growth (density, length, color, etc.) but there are most likely large trends that exist that you could pick up on with a simple glance. As far as evolutionary time frames, they do not have to be that large (geologically and historically speaking). If you compare the heights of our ancestors - let's say at least the last 100 to 200 years to beyond. People were much shorter. Today we're bigger. This may simply be tied to the fact that cultures have generally went from scavengers to farmers, i.e. food supply went from sporadic to fairly stable. This would give people better nutrition and allow them to grow larger.

The exceptions to the rule are "mutations" and this is where evolution happens. It's when those mutations are preferable for the survival of a species.

I would also doubt that us starting to shave however many years ago affected our genome.


Ahh...reproduction is also a potential "cause"

[The Nid Hog]

It's so we can regularly enjoy a nice shave and a haircut.

[Taylor of Bank Street]

Awesome thread. I'm going to check back on this to see if an answer is reached.

Having just enjoyed a leisurely shave on a day off, I'll have to admit that, 'It's so we can regularly enjoy a nice shave and a haircut' is my favourite answer thus far.

The other answers, or most of them, seem to break down into two groups, continually growing facial hair either as some form of i) survival advantage or ii) an aspect of sexual selection. I had never thought of it before but Commander Q makes a good case for the latter. Traits acquired for sexual selection purposes are fascinating in that they can sometimes develop to the point where they actually make survival more difficult for the individual, think peacocks or the extinct Irish elk.

Another factor to throw in to make it more complex than it already is, is that selection processes don't particularly care if you live to be 85 and have hair 20 metres long. From an evolutionary perspective, you just need survive long enough to have and rear children. At this point in our lives perhaps our hair would still be at a manageable length?

Wish I knew but am going to stay tuned to listen to what others have to say. I remember reading about this book: 'Why Do Men Have Nipples? Hundreds of Questions You'd Only Ask a Doctor After your Third Martini'. This or one of it's follow-ups might have the answer.

[Threeme2189]

This is a very interesting topic for conversation.
You guys have made some excellent points and I really can't think of anything else to add...
I find the whole topic of evolution very interesting, and am currently listening to some Richard Dawkins audiobooks.

[taco8slo]

The answer is quite simple; God created us this way.

I agree.

[rockviper]

Longer whiskers let us store extra food like chicken wings. Shorter beards can only hold smaller crumb-like snacks.
Gee.... Now I'm hungry.

[moto_mike]

In the evolution picture, this would seem to be counterproductive and require man to absolutely take a positive action to cut the hair at some point before it became a liability to eating, walking, sanitation, survival, etc.

I forgot to mention this idea...but James mentioned it. Hair does fall out eventually on its own. Granted it may get really long before that happens, but it would shed. The major setback would be sanitation. This would promote disease which all in all would really just shorten life expectancy. So we would be more inclined to evolve to complete our life cycle in a shorter time frame. But that's one reason we live longer and have less crazy epidemics like the Plague today - better sanitation.

I mean only several centuries ago, taking a bath was sacrilegious.

[barrycv]

Disclaimer: I am no biologist / anthropologist either, just a dorky engineer.

My guess is that hair was first & foremost a functional item. It provided protection (physical barrier & heat retention) to critical areas as well as served as other aids in everyday life (lubrication at joints, a quick & convenient carrier for an infant or misc goods, etc).

I would think that the sexual selection portion of it came about as a result of having hair, but that fact nonetheless kept the trait going. Taylor of Bank Street has a very good point in that life expectancy was quite short. Your viable reproductive years were from early teens to basically when you died off - maybe early 20s to 30 max. There was no need / advantage to have hair production stop at any point.

[YuriZhivago]

Great responses, all of you! Enjoying the humor, too.

Some additional points: Is a man's continual facial hair growth a secondary gender characteristic for reproductive selection as it doesn't seem necessary for survival since females lack the growth of thick facial hair? Did environmental adaptation characteristics affect facial hair growth patterns in men, contrasting, perhaps Asians versus the Indian subcontinent, or for that matter my Siberian ancestors? I posed this question, and there have been some valid points made about our actual longevity prior to the scientific/medical revolution, because I'm somewhat curious as to why the evolutionary process would essentially force us to use some type of external tools to effect a grooming process. (My chest hair just grows out to relatively consistent length and stops.) It is estimated that the average man's hair grows approximately 1cm/mo or 12cm/yr. At thirty years of age, assuming male puberty was around age 14, that would be 1.9 meters or about 6 feet! Could you imagine our ancestors beards and hair without combs or any real maintenance near the end of their lifespan of perhaps thirty years? (Thus my linking this topic with the quintessential and penultimate grooming concerns discussed in these forums.) Again, as most mammals have a limited-length coat that might seasonally shed and change in length and density, what factors would have caused man's facial hair to evolve to a continuously growing characteristic? Granted hair, or fur, was for climatic protection and to a lesser extent, protection against predatory creatures who ended up with only a mouthful of hair.

I just speculate on these points as they are fundamental to the entire content of this wonderful site.

[madcap3693]

Heres an interesting article in the NY Times regarding Human body hair evolution...

http://www.nytimes.com/2003/08/19/science/why-humans-and-their-fur-parted-ways.html?pagewanted=all&src=pm

[moto_mike]

Heres an interesting article in the NY Times regarding Human body hair evolution...

http://www.nytimes.com/2003/08/19/science/why-humans-and-their-fur-parted-ways.html?pagewanted=all&src=pm

Very interesting! Certainly touches and expands on all the points brought up here.

[Oblique Human]

Could evolution or adaptation and our ability to think and cut our facial and cranial hair, exposing our skin to the environment, have lead to the human genome being altered to permit such unrestricted hair growth?

No, I believe its that blasted Mach 3.

[Kentos]

If you subscribe to evolutionism, SOMETHING must have happened to favor a man with Facial Hair. Maybe it served as an identifier of having reached sexual maturity. Guys with no beards wouldn't get to play and thus pass on the no facial hair gene.

[Rob72]

I respectfully disagree.

I'm not a biologist, however, I am a scientist. A geologist to be more specific.

James makes some great points. I would like to throw past climate into the ring. We lost a lot of hair coming out of the last ice age. What's left may be simply a reaction to the climate of the different regions of the world where people reside and the way our genome responded to our environment. Obviously, not every single person of a particular region has the same hair growth (density, length, color, etc.) but there are most likely large trends that exist that you could pick up on with a simple glance. As far as evolutionary time frames, they do not have to be that large (geologically and historically speaking). If you compare the heights of our ancestors - let's say at least the last 100 to 200 years to beyond. People were much shorter. Today we're bigger. This may simply be tied to the fact that cultures have generally went from scavengers to farmers, i.e. food supply went from sporadic to fairly stable. This would give people better nutrition and allow them to grow larger.

The exceptions to the rule are "mutations" and this is where evolution happens. It's when those mutations are preferable for the survival of a species.

I would also doubt that us starting to shave however many years ago affected our genome.


Ahh...reproduction is also a potential "cause"

We are "larger" because of better nutrition- Germany is actually taking the stature lead, btw. This is not evolutionary, but an adaptation to an environmental factor- it is not static. We've been agriculturally based, socially, for better than 4000 years, and most of that time we spent under 5'. This changed with the development of better growing practices, and grain and meat processing.

Asiatics have some of the lightest hair-growth patterns, and have inhabited some of the coldest climates continually since before written history. Facial hair is inadequate for providing insulation, and neither the torso nor thighs (both significantly greater sources of heat generation/loss) are nearly so covered. We don't, "lose the majority of body heat from the head", BTW. Wooly-mammoth-man doesn't fly.

[Rob72]

If you subscribe to evolutionism, SOMETHING must have happened to favor a man with Facial Hair. Maybe it served as an identifier of having reached sexual maturity. Guys with no beards wouldn't get to play and thus pass on the no facial hair gene.

MPB (Male Pattern Baldness) is the most visible indicator of high testosterone. This is also only true among the mix of Western and Eastern European tribes.

[Neognosis]

We don't, "lose the majority of body heat from the head", BTW.

I think it is a matter of semantics. All things equal, there is no more heat loss per exposed area through the head, as explained here:

http://wildernessmedicinenewsletter....d-hypothermia/


But when the subject is wearing clothes and no hat, I think it's common sense that heat is lost faster through exposed areas.

Regarding the hair discussion, don't forget that all untended hair, even caucasian hair, dreads with time. So while we are thinking that uncut hair would be horribly inconvenient, consider that dreadlocks would not be nearly as troublesome as loose, individual strands of hair. I think dreadlocks would also be easier to cut off with a rudimentary stone tool than it would be to cut individual strands of hair.


I suspect that man's ability to tie back or cut off his hair might have coincided with the change that allowed our hair to grow longer. I hypothesize that before we had the ability to cut or tie hair out of the way, we probably didn't have the genetics that allow it to grow so long. When we achieved the ability to grow longer hair, we also were likely at the point where we could manage it, so the mutation for long head and facial hair probably didn't carry with it any significant disadvantage that would have caused it to be weeded out through natural selection.

Nothing but chance. We happened to have a mutation for long hair, at a time when we happened to have acquired the skill to tie it back and cut it. This is my theory.