Human scalp hair as a thermoregulatory adaptation

Significance

The evolution of human scalp hair might be explained by
thermoregulation pressures experienced in hot and arid environments.
Bipedal posture and a hairless body may have necessitated the
development of scalp hair to minimize heat gain from solar radiation,
particularly in hominins with large brains. We used a thermal manikin
and human-hair wigs to examine this thermoregulatory hypothesis. We
confirm that scalp hair reduces heat gain from solar radiation and
find an effect of hair morphology. Our results show that tightly
curled hair provides the most effective protection for the scalp
against solar radiation, while minimizing the need for sweat to offset
heat gain.

Abstract

Humans are unique among mammals in having a functionally naked body
with a hair-covered scalp. Scalp hair is exceptionally variable across
populations within Homo sapiens. Neither the function of human scalp
hair nor the consequences of variation in its morphology have been
studied within an evolutionary framework. A thermoregulatory role for
human scalp hair has been previously suggested. Here, we present
experimental evidence on the potential evolutionary function of human
scalp hair and variation in its morphology. Using a thermal manikin
and human hair wigs at different wind speeds in a temperature and
humidity-controlled environment, with and without simulated solar
radiation, we collected data on the convective, radiative, and
evaporative heat fluxes to and from the scalp in relation to
properties of a range of hair morphologies, as well as a naked scalp.
We find evidence for a significant reduction in solar radiation influx
to the scalp in the presence of hair. Maximal evaporative heat loss
potential from the scalp is reduced by the presence of hair, but the
amount of sweat required on the scalp to balance the incoming solar
heat (i.e., zero heat gain) is reduced in the presence of hair.
Particularly, we find that hair that is more tightly curled offers
increased protection against heat gain from solar radiation.

Open access:
https://www.pnas.org/doi/10.1073/pnas.2301760120

"hot and arid environments".
That doesn't sound like aquatic ape.

:-DDDDDD
Never seen such an idiotic fanatasy!
That's why all kudus have lots of hair on their heads, and I'm bald and I have to shave my beard+moustache.
And my beard is to protect my belly from sunbeams...
:-DDDDDD

"Humans are unique among mammals in having a functionally naked body with a hair-covered scalp. Scalp hair is exceptionally variable across populations within Homo sapiens. Neither the function of human scalp hair nor the consequences of variation in its morphology have been studied within an evolutionary framework.

Liars, see my Med.Hypoth., Hum.Evol. etc. papers, or see only my book p.41-48 illustr.
How is it possible that PNAS allows such idiocies???

Enough nonsens!
:-DDDDDD

From my 1st paper (1985):
D. The hair follicles on the human head
In humans, the head hairs are normally shorter in men than in women; a male’s uncut neck hairs, beard & moustache grow as far as his chest. Moreover, humans have unique “sebaceous follicles” (17): in our neck, face & upper torso, there are very large sebaceous glands that are not connected with terminal hair follicles as in other regions of the body or in other mammals, and that ooze the sebum out of the skin. Pinnipeds also secrete quantities of sebum, and aquatic birds have large oil glands (16). Like the growth of the beard & moustache, the activity of human sebaceous follicles starts in puberty under androgen influence (dihydrotestosteron DHT) and is more prevalent in boys than girls, as is acne, a typically human disease of inflammated sebaceous follicles.
It is possible that, because of their location, the sebum of these follicles once kept the neck hair, beard & moustache supple, fatty, waterproof & well-fitting to the body, so that the “manes” were not dispersed by the water while swimming. Sebum & long head-hairs together made the male’s neck completely streamlined (Figure 1).
The convergent evolution of the integument of male Homo & male Eumetopias (as compared to the primitive Primates or Carnivora) is quite remarkable: both developed body nakedness, thick SC white fat, extensive superficial venous networks in the limbs, abundant sebum secretion, long coarse neck-hairs & a tendency to nakedness at the top of the skull (& perhaps thermoactive sweat glands, see B).
Morgan (2,6) supposed that women’s head hairs, growing longer than men’s, and not kept together by abundant sebum, once enabled the newborn baby to accompany its mother in the water by grasping her hair. This fits in with other data. The baby’s SC fat grows rapidly from the 34th fetal week until a few months after birth, so the baby is born with a thick layer of white fat (c 16% of its body weight, see B). As such, it is an exception among land-born mammals; even newborn Cavia has much less SC fat (21). The human newborn also shows what M.McGraw called “swimming behaviour”: when held in water, the baby makes well-coordinated swimming-movements, and it even stops breathing, and shows a pronounced bradycardia when its head is immersed (2,22).
....
Fig.1 – Reconstruction of a swimming ancestor
If the AAT is true, our ancestors must have been more or less streamlined, in order to reduce water resistance and heat loss. I have tried to reconstruct a side-view of a late-Pliocene male Homo swimming under water. The sketch is based on the picture of a human skeleton (49), that is modified as follows. The head is dorsiflexed (to set the eyes in the swimming-direction, as in all mammals swimming under water). The brain skull is lower, smaller & shifted dorsally (as in the “platycephalic” Java man). The jaws are more robust, a chin is missing (as in all extinct hominoids). The foramen magnum lies a little bit more dorsally (as in e.g. A.africanus (50)). Sacrum & coccyx are somewhat less projecting dorsally (as in early hominid pelves: before the great enlargement of the newborn’s brain, the present-day broad pelvic passage was unnecessary). The knee region is a bit smaller, and the tibia & ankle region is a lot smaller (as in australopiths (51)), but the feet are rel.broader (as in the Laetolil footprints, see C). Upon this modified skeleton, I have sketched a somewhat thick-bellied man (see B), with baldness, uncut neck-hair, beard & moustache (see D). The dorsally projecting portion of the glutaeus maximus muscle is drawn a little bit smaller (since only in complete bipedality it became important in fully extending the hip joints (52).)

Op donderdag 8 juni 2023 om 20:38:27 UTC+2 schreef littor...@gmail.com:
> :-DDDDDD
> Never seen such an idiotic fanatasy!
> That's why all kudus have lots of hair on their heads, and I'm bald and I have to shave my beard+moustache.
> And my beard is to protect my belly from sunbeams...
> :-DDDDDD
> "Humans are unique among mammals in having a functionally naked body with a hair-covered scalp. Scalp hair is exceptionally variable across populations within Homo sapiens. Neither the function of human scalp hair nor the consequences of variation in its morphology have been studied within an evolutionary framework.
> Liars, see my Med.Hypoth., Hum.Evol. etc. papers, or see only my book p.41-48 illustr.
> How is it possible that PNAS allows such idiocies???
>
> Enough nonsens!
> :-DDDDDD

littor...@gmail.com wrote:
> From my 1st paper (1985):

Out of date.

> Morgan (2,6)

who wrote science fiction for TV

> > From my 1st paper (1985):

Sta.Savanna-believer:
> Out of date.

:-D Not at all:
after so many years, the savanna-believe are still miserably incapable of providing 1 single little objection to this detailed description of human skin follicles:
for some reason (not for running after antelopes... :-D), humans have 3 sorts of hair follicles: terminal, vellus & sebaceous:

The hair follicles on the human head

1) Humans head hairs are normally shorter in men than in women:
a male’s uncut neck hairs, beard & moustache grow as far as his chest.

2) Humans have unique *sebaceous follicles*, not seen in other primates:
in our neck, face & upper torso, we have very large *sebaceous glands* that are not connected with *terminal hair follicles* as in other regions of the body or in other mammals:
they ooze the sebum out of the skin.
- Pinnipeds also secrete quantities of sebum,
- aquatic birds have large oil glands.
Like the growth of the beard & moustache, the activity of human sebaceous follicles starts in puberty under androgen influence (DHT, boys>girls),
it is more prevalent in boys than girls, as is acne, a typically human disease of inflammated *sebaceous follicles*.
Because of their location (& no soap!), the sebum of these follicles once kept the neck hair, beard & moustache supple, fatty, waterproof & well-fitting to the body,
so that the “manes” were not dispersed by the water while swimming:
sebum & long head-hairs together made the male’s neck completely streamlined.
The convergent evolution of the integument of male H.sapiens & male Eumetopias (vs terrestrial Primates or Carnivora) is very remarkable:
both developed in parallel:
- body nakedness,
- thick SC white fat,
- extensive superficial venous networks in the limbs,
- abundant sebum secretion,
- long coarse neck-hairs,
- nakedness at the top of the skull (male pattern alopecia),
- thermo-active sweat glands, secreting sodium+water.

Elaine Morgan suggested:
women’s head hairs (growing longer than men’s, and not kept together by abundant sebum) once enabled the newborn baby to accompany its mother in the water by grasping her hair.
This fits in with other data:
- the baby’s SC fat grows rapidly from the 34th fetal week until a few months after birth:
- the baby is born with a thick layer of white fat (c 16% of its body Wt):
it is an exception among land-born mammals (even newborn Cavia - a rel.fat animal - has much less SC fat).
The human newborn also shows what M.McGraw called “swimming behaviour”:
when held in water, the baby makes well-coordinated swimming-movements, it even stops breathing, and shows a pronounced bradycardia when its head is immersed.

IOW, only incredible imbeciles deny that Pleistocene human ancestors were semi-aquatic!
(Some of these idiots even believe their ancestors ran after antelopes... :-DDD)

> > Morgan

corrected the above text (the MS) for me...
Thanks, Elaine! :-)
It's incredible but there are still "anthropologists"(they think) who afro- & anthropo-centrically believe their ancestors lived in Afr.savanna...

Primum Sapienti wrote:

> littor...@gmail.com wrote:
> > From my 1st paper (1985):

> Out of date.

Nuclear fission: 1938.

You have no idea what even is an argument!

-- --

https://jtem.tumblr.com/post/721153190279643136

Op maandag 26 juni 2023 om 06:15:42 UTC+2 schreef JTEM is so reasonable:

> > > From my 1st paper (1985):

kudu runner's only "argument":
> > Out of date.

:-D
The idiot: after all that time he's as stupid as he was before...

> Nuclear fission: 1938.
> You have no idea what even is an argument!

Yes, JTEM, some of these fools are *incredibly* stupid.

Our problem is that they're wrong in so many ways:
- apiths=Afr.ape ancestors,
- Plocene Homo in S.Asia,
- not running but wading,
- etc.etc.

I also began with following the idea that we evolved in Africa from chimp-like ancestors:
forest->savanna = QP->BP "freeing hands" :-D
And if I hadn't read Elaine's "Descent of Woman" (already in 1974 IIRC), I was perhaps still believing this nonsense...

Ape+human evolution is generally rather well understood today.
What I still don't understand is how stupid some self-declared "scientists" can be...

Desmond Morris 1967 "Naked Ape" already mentioned the possibility of a (semi)aquatic past (cf Alister Hardy & others before Hardy). "Everybody" at that time had read Morris's enormously popular book (taboo word "naked"!), but at the time I forgot about it, until I had read Elaine's "Descent of Woman" (begin of feminism). I found our waterside past very (bio)logical, but at the time (1972?) I was preoccupied by the question: if "survival of the species" is correct, why do humans or animals kill conspecifics?? In 1974 or 1975 I realised the solution (sociobiology): survival of DNA (not of the species) and I went to "aq.ape".

What I have done, I think, is making the times & places more realistic... :-)
-not 10 Ma (Hardy) or even 5 Ma (Elaine), but only c 2 Ma?
-not Africa, but S.Asia
-apiths=Afr.ape-ancestors specified: afar.->boisei=Gorilla // africanus->robustus=Pan
-not only we are BP, but all Hominoidea were aquarboreal
-gradual evolution: arboreal->aquarboreal->littoral->...
-even only 2 yrs ago, I realised:
hominoid splittings <- plate tectonics
= obvious & great improvement IMO... :-)
_____

Op maandag 26 juni 2023 om 11:54:14 UTC+2 schreef littor...@gmail.com:
> Op maandag 26 juni 2023 om 06:15:42 UTC+2 schreef JTEM is so reasonable:

> > > > From my 1st paper (1985):

kudu runner's only "argument":
> > > Out of date.

> :-D The idiot: after all that time he's as stupid as he was before...

> > Nuclear fission: 1938.
> > You have no idea what even is an argument!

> Yes, JTEM, some of these fools are *incredibly* stupid.
> Our problem is that they're wrong in so many ways:
> - apiths=Afr.ape ancestors,
> - Pliocene Homo in S.Asia,
> - not running but wading, etc.etc.

> I also began with following the idea that we evolved in Africa from chimp-like ancestors:
> forest->savanna = QP->BP "freeing hands" :-D
> And if I hadn't read Elaine's "Descent of Woman" (already in 1974 IIRC), I was perhaps still believing this nonsense...

> Ape+human evolution is generally rather well understood today.
> What I still don't understand is how stupid some self-declared "scientists" can be...

littor...@gmail.com wrote:
>
>>> From my 1st paper (1985):
>
> Sta.Savanna-believer:
>> Out of date.
>
> :-D Not at all:

Yes it is. It's gone nowhere.

Primum Sapienti wrote:

> Yes

Nuclear fission: 1938. According to you it's "Wrong"
because it's "Out of date."

-- --

https://jtem.tumblr.com/post/721666107169292289

JTEM is so reasonable wrote:
> Primum Sapienti wrote:
>
>> Yes
>
> Nuclear fission: 1938. According to you it's "Wrong"
> because it's "Out of date."

Fission is well proved and used. AA, well...

Primum Sapienti wrote:

> Fission is well proved

Just like so called "Moderns" interbreeding with Neanderthals was,
generations before your religious faithful accepted it.

And Aquatic Ape. DHA alone proves it. As does Coastal Dispersal.
And other evidence.

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https://jtem.tumblr.com/post/723706649198690304