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James
ENG 101
5/21/08
Nacua
HAIR
Scientists have examined out how we modern humans are connected to our
ancestors for years. Through countless hors of research, anthropologists and scientists
have made strides in connecting modern man with our old relatives through fossil
examinations, tool making, even in biological ways, but there is still many more
unanswered questions on how Homo Erectus, Lucy or even Sahelanthropus tchadensis
and much more species could possibly be related with us physically and genetically. If
we do indeed all come from a common ancestor, then how could we have evolved to
have no hair on our body compared to our primate cousins as well as having diverse types
of hair color? Hair is universal among us humans but, is the variations of the hair such as
color and texture as well as distribution which tells us the geological adaptations our
ancestors made so their hair is unique to that type of race. While everyone has hair, no
one really stops to think about why we have it or why the differences exist. The
evolution of hair from millions of years ago starting with our primate ancestors can be
separated in four categories. We can take a chronological approach, starting with
defining what hair is (head hair), androgenic hair (body hair), the differences or
similarities between the two, theories on how we lost our body hair over millions of
years, and finally the varieties of hair throughout the world.
Not knowing exactly what hair is and what it’s made of can confuse a person
especially when the discussion will lead to the mutation of hair. According to Stedman's
Medical Dictionary, hair is “One of the fine, keratinized filamentous epidermal growths
arising from the skin of the body of mammals except the palms, soles, and flexor surfaces
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of the joints; the full length and texture of hair varies markedly in different body sites”
(357). Let’s delve deeper into this word. Hair protrudes from the epidermis which is the
upper or outer layer of the two main layers of cells that make up the skin. Deep within
the epidermis, one layer below, you have the dermis where the hair follicle exists. A Hair
follicle is a sac from which a hair grows and into which the sebaceous (oil) glands open.
The follicle is lined by cells derived from the epidermal layer of the skin. Sebaceous
glands that are found surrounding the hair follicle will determine an individual’s thick
hair density. We can see how hair is grown, but what about the essential ingredient of
what makes hair? This can be answered by the word “keratin”. Stedman's Medical
Dictionary defines it is a “collective name for a group of proteins that form the
intermediate filaments in epithelial cells”(450). In other words, the epithelial is another
way of saying epithelium which is the outside layer of cells that covers all the free, open
surfaces of the body including the skin and the group of proteins that form in the
epithelial are keratins (fibrous protein) which is the main element of hair fiber. It is
Interesting to note that only mammals have hair growing on them compared to insects
such as spiders, they have something called “bristles”. These bristles are made up of
polysaccharide called chitin. Species that are not in the mammalian side for example
dogs have fur not hair; plants have “hair” called trichomes. The hair on the scalp, where
hair is usually densest and longest, the average total number of hairs is between 100, 000
and 150, 000. Human hair grows at a rate of 10-13 mm/month.
Body hair falls into classes and each one seems to be determined by an
individual’s age or stage in life. We basically have three types of androgenic hair or what
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is most commonly known as body hair. The three classes are Lanugo hair, Vellus hair
and finally Terminal hair. Lanugo hair, this is beginning or first type of hair you will
ever start to develop over certain parts of your body. Lanugo is described according to
Merriam-Webster as a “very fine, layer of downy, slender hairs” (“lanugo”124). The
lanugo hair mainly covers your body while you were still a fetus and occurs as a normal
part of gestation, but is usually shed and replaced by vellus hair at about 40 weeks of
gestational age. After the lanugo hair has been shed either before or shortly after birth
the second stage of hair type will start to grow. Vellus hair is short, fine, unpigmented
hairs widely known as “peach fuzz” hair. This type of hair covers every part of the body
except the palms of the hands, the soles of the feet, undersurfaces of the fingers and toes,
and a few other places. It is mostly evident on women and children because they tend to
have less terminal hair to hide it. The third stage and final type of androgenic hair to grow
is the terminal hair. This will not replace the vellus hair before it but rather supplements
it and is different from that of the vellus hair. Terminal is defined “longer, coarser,
thicker and darker than the shorter and finer vellus hair. It can be found on the scalp,
beard, armpits, and pubic area” (“Hair”) Puberty can set off the growth of terminal hair
and based on the androgenic level (male hormones) of a person, it will determine the
growth rate. In contrast to terminal hair growth produced based on the level of
hormones, vellus hair growth is not affected by hormones. The name androgenic hair
comes from the hormones the body will produce throughout their body, androgen. Your
hair follicles will react to the amount of hormones your body is giving out, mainly
testosterone, and will develop terminal hair from some of the already existing vellus hair.
In the case of the distribution of body hair on both male and female, the men will win
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this. As stated before the hair that grows on you is based on your hormone level. An
individual rising of androgens will be the deciding factor for the development and
quantity of androgenic hair. Women tend to have much more vellus hair, but it is nothing
compared to their male counterparts who have vellus and terminal hair growing on our
legs, arms, back of the neck and upper body. Hair basically reacts to hormones,
particularly testosterone, which males have plenty of. Although women also produce
testosterone, it’s still low about forty to sixty times lower than of hairy males.
Humans are in a class of their own among our monkey brethren, in terms of body
hair. A side by side comparison of a human and a chimpanzee can clearly show our
similarities. Yes, we have similar limbs, yes their infant’s looks very much like ours, yes
chimpanzees have 97%–98% identical to that of a human, but what about the differences.
Take a good look at the body and you’ll feel almost dim-witted by not realizing it in a
split-second. It’s the abundant coating of hair the monkeys have all over them that we
humans don’t have.
We’ve come to the first theory as to why humans don’t have body hair. The first
theory is the body-cooling hypothesis, probably the most-known theory for hair loss. As
the theory goes, our early ancestors traveled to the open African savanna environments,
saying goodbye to their familiar forest shaded surroundings. Along with change of
environments, bipedalism is also brought up and surprisingly goes with loss of hair.
While our ancestors were gathering food in the savanna, they would have less exposure
to the sun due to their upright posture compared to other quadrupeds. The sun would be
raining down on the top of their head instead of their back. The loss of body hair would
make it easier to radiate heat back into the environment or to lose heat by convective
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cooling from the wind (Wheeler). Along with any other theories, there is always
someone or a group of individuals to pounce at it. Countering with their own research
that would prove that this particular theory is false, for example “naked skin is actually a
worse solution when the entire day is taken into account: more heat is dissipated from
daytime exposure and, at night time, more heat is lost” (Armaral). Brazilian physicist
Armaral has a strong argument, considering that during the night-time in the deserts do
get cool, about 32°F due to extremely low humidity. What could our ancestors have been
using to keep warm during the night? Maybe it was a large collection of twigs and was
then formed into a blanket? Or a big group hug to increase body temperature? Surely it
was not their body hair to keep them warm because it was gone by now, so I guess the
more you dig deeper to a theory the more questions will arise than anwers.
Losing hair for comfort because of the sun’s harsh heat is plausible but, an aquatic
theory of hair loss is far-fetched. Although many other people have proposed this theory
such as the ancient greek philosopher Anaximander and the German biologist Max
Westenhõfer, who put it in an evolutionary context, it was marine biologist Sir Alister
Hardy who gained much of the attention of this theory mainly because of his speech to
the British sub-aqua club in Brighton, England on the fifth of March 1960. His theory
explains that “between 6 and 8 million years ago, the ancestors to the homonids had a 1
or 2 million year phase of aquatic or semi-aquatic existence” (Morgan 1997). You can
say that the physical traits to prove we’ve had a few swimming lessons millions of years
ago, are the slight webbings on your hands, the hooded nose which prevents water from
entering the nostrils and the greasy skin we humans exhibit which you might say is a trait
gained for waterproofing the body. Based on this theory, hair is not a much appreciated
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trait for underwater which in turn will make our ancestors start to loose their hair. Maybe
it’s because hair can weigh you down when they get out of the water and can obstruct
your vision, nose and not hydro dynamically sound. This makes you wonder, of the sea
creatures today, they seem to have a certain shape to them, teardrop shape, to swim
around flawlessly. Even though there is some substantial evidence to prove our aquatic
phase from the nose, greasy skin and some fossils that have appeared on some coasts,
there are gaps in the theory to disprove it. Take for example the eating habits of our
ancestors as discussed by Carlson and Kingston “In our report investigating links
between omega-3 (n-3) fatty acids and hominin encephalization, we concluded that the
regular consumption of aquatic resources rich in preformed docosahexaenoic acid may
not have been essential given a varied diet of wild terrestrial foods”. We are basically
told that there was sufficient food on land and therefore no need for an aquatic life
whatsoever. If there was the right type of food on land at that time so what’s the purpose
of the water visit? You can say a group of hunters stumbled across some fish along the
coastline and decided that this will be their main food and one thing led to another, over a
couple of years hunting in the ocean, developed some aquatic features and hair loss.
A vast amount of androgenic hair combined with ectoparasites and sexual
relations brings us to our third and final theory of hairlessness as an adaptation.
Ectoparasites are in no way pleasing while they are biting us, our early relatives thought
the same thing too so; they shed some hair to get rid of these parasites. These
ectoparasites would cause huge irritations to our ancestors. Considering that early
homonids were still inhabiting Africa and the population was predominantly hunter
gatherers and lived in closed areas, these ectoparasites would live on their body. The
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transactions of these bugs were in a high rate. With the assumed plucking of their hair to
reduce or eliminate parasite population on oneself, this action accidentally led to sexual
selection. When we are left with just hair on our pubic area and the top of our head, our
ancestors must’ve thought that these were the parts of the body to attract a mate. Pubic
hair as stated by Page and Bodmer “contains warmth and humidity … especially
conductive to pheromonal signaling between man and female.” With the attraction of a
mate based off the exposure of head and pubic hair, this will initiate reproduction of this
certain individual hair gene and creating more. The hair left on our head is a sexual and
natural selection because the hair will reduce exposure, in contrast to overall body
exposure with quadruped creatures, to the sun and attractiveness to the opposite sex.
The variation of hair is also a most fascinating topic. The types of hair color, such
as red, blonde, black, brown and gray are all differentiated biologically. There are many
hair colors out there but it all depends, as Jessica Marshall states “on the pigmentproducing melanocytes in the hair follicles, which brings out melanin to the cells whose
corpses make up each hair strand.” Blonde hair has less melanin than light brown or
black hair and as for the case of red haired individuals they have mutations in a gene
called MC1R. Its effect is to block production of black-brown melanin—the most
common form (Marshall). Black hair is the most dominant trait in all ethnicities but is
less dense compared to other hairs. Brown is a close second for people with African,
European, Middle Eastern, and Native American ancestry. Blondes and red-head are
mostly found in European regions, blondes being rare and known to be recessive and
occurring in approximately 10% of the world's population, even rarer occurrences are the
red- haired people. Gray hair is by age, the older you are the more gray hair appears, but
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in some cases gray hair may instead be caused by a deficiency of B12 (involved in the
metabolism of every cell of the body, especially affecting the DNA synthesis) or a
thyroid imbalance. As for the case for having no hair, or in other word bald, the causes
are limitless. The list can go on to certain shampoos being the culprit to lack of nutrients
to increase amount of hormones. For the case of how baldness came to be, there has been
studies and according to Muscarella and Cunningham’s research,
“baldness evolved in males through sexual selection as an enhanced
signal of aging and social maturity, whereby aggression and risk-taking decrease
and nurturing behaviors increase. This may have conveyed a male with enhanced
social status but reduced physical threat, which could enhance ability to secure
reproductive partners and raise offspring to adulthood.”
This is by far a great depiction of bald people, as oppose to the ugly, bad genes that
would cause baldness comment. If you have no hair and the only thing you are left is, is
your personality and maturity to show that you are still attractive to the opposite sex and
then by all means flaunt it. For this can spread your genes, gaining much sexual
intercourse. If you don’t have hair as well as a personality, much luck to you on finding a
mate according to Muscarella and Cunningham’s research.
There have been some theories as to the spreading of blonde hair at the end of the
Ice Age. Northern European women who mainly had blonde hair started to increase in
population because there was a food shortage 10,000 to 11,000 years ago. With the dark
haired, and dark eyed men started searching for food which “required long, arduous
hunting trips in which numerous males died, leading to a high ratio of surviving women
to men and the blondes increased.”(“How Blondes Evolve”) Now, it does not state that
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the amount or existence of blonde men but, the blonde women population did increase
because they became favorable for breeding much like today. There must’ve been
something that clicked in the mind of hunter to all of a sudden make a blonde woman so
much more appealing over a black haired woman. Perhaps it’s the blondes exotic, new
hair color that drove men to favor them much more than the rest.
Hair, if you want to believe it or not, an enigma. Sure we can see that hair is
present on people or not and the color they exhibit, but you can never explain the
evolution of hair. How is it we end up to have just have hair on our head and our pubic
hair when we once an abundant amount of hair all over our body? We can only think of
theories as to how this could have happened because hair does not fossilize very well to
be studied. The majority of paleoanthropologists and geneticists have much more
important research to do. You look at the phenotype, genetic similarities, and brain
functions with early homonids compared with parasites biting on our ancestors’ nether
regions to cause hair loss, which do you think will give you a Nobel Prize?