On Friday, March 25, 2022 at 12:16:53 PM UTC-4, DD'eDeN aka note/nickname/alas_my_loves wrote:
> On Friday, March 25, 2022 at 12:02:35 PM UTC-4, DD'eDeN aka note/nickname/alas_my_loves wrote:
> > On Tuesday, March 15, 2022 at 2:55:01 PM UTC-4, DD'eDeN aka note/nickname/alas_my_loves wrote:
> > > On Monday, March 14, 2022 at 9:22:43 PM UTC-4, DD'eDeN aka note/nickname/alas_my_loves wrote:
> > > > On Monday, March 14, 2022 at 8:11:44 PM UTC-4, Paul Crowley wrote:
> > > > > On Sunday 13 March 2022 at 22:31:51 UTC, DD'eDeN aka note/nickname/alas_my_loves wrote:
> > > > >
> > > > > >> So what's the need for that extremely
> > > > > >> expensive hair? If melanated naked skin
> > > > > >> protects against UV rays, why have that
> > > > > >> extraordinary hair? ('Extraordinary' in
> > > > > >> that no other mammal has anything
> > > > > >> like it.)
> > > > > >
> > > > > > Melanin in skin: stops ultraviolet light penetration beyond the (dead)
> > > > > > epidermis layer.
> > > > > >
> > > > > > Melanin in hair: stops infrared light (heat) penetration at the (coiled dead)
> > > > > > hair layer, which reduces the temperature of the head (including brain and
> > > > > > blood vessels).
> > > > > >
> > > > > > Homo's large brain has large heat production, sweating depends on
> > > > > > evaporation, in perpetually hot humid climates sweating is more effective
> > > > > > with tightly coiled but lofty hair than with damp flat hair clinging to the scalp.
> > > > > Your scenario implies that sweating was
> > > > > a routine everyday matter.
> > > > All primates sweat. Humans sweat at 3 levels: incipiently, during sleep (hot or cold) while body is inactive, lightly while body is active but not strenuously so, and heavily while active strenuously so. Fever is our body's reaction to an attack on our metabolism, fight-or-flight is our body's reaction to a perceived attack on our body, both use sweating defensively.
> > > > I do not see
> > > > > it that way. The hominins would have
> > > > > needed a good supply of water, and that's
> > > > > often hard to find.
> > > > Like modern humans, archaic hominins lived near (but not in) shallow freshwater.
> > > > Sweating was IMO
> > > > > primarily for emergencies -- such as when
> > > > > they got into fights, or suffered fevers.
> > > > That is heavy sweating, a comparatively rare occurrence, and a poor way to cool since it excretes faster than it evaporates, unlike incipient and light sweating. Dripping sweat is both inefficient and ineffective, and leads to dehydration.
> > > > > Those who could lose heat by sweating
> > > > > survived better than those who couldn't
> > > > > -- maybe their reserves had run out.
> > > > N/A.
> > > > > So, under my scenario, the 'tightly coiled
> > > > > hair' would have had little significance
> > > > > as regards sweating. It could not have
> > > > > evolved for that purpose.
> > > > Under extreme sweating, scalp hair is irrelevant, fluid sweat pours off anyway.
> > > > > > Gareth Morgan:
> > > > > > "In plain English, body heat is generated by mitochondria. Normal cells have
> > > > > > between 2 and a couple of thousand mitochondria. Heart cells have around
> > > > > > 5,000 but brain cells have an estimated two million mitochondria per cell.
> > > > > > The brain is a colossally effective furnace. This is important because the heart
> > > > > > is the most vulnerable organ in the human body to cold. The blood from the
> > > > > > brain, which comes out much hotter than it goes in, goes directly to the heart.
> > > > > > In terms of natural selection this is very much the difference between rapid
> > > > > > death from hypothermic heart failure and a chilly dip."
> > > > > Thanks for this. I've tried to look into it, but
> > > > > it seems to be an field of active research
> > > > > with relatively few answers at present.
> > > > > (E.g. I'd like to know if other species brains
> > > > > had the same proportion of mitochondria.)
> > > > >
> > > > > However, in outline, it supports my argument
> > > > > that large brains could have acted as a 'heat
> > > > > resource' for a species where individuals
> > > > > found themselves in cold water (perhaps, on
> > > > > average, less than once in a lifetime) and
> > > > > where the larger-brained had better chances
> > > > > of survival.
> > > > N/A.
> > > > > Note that I'm changing my terminology from
> > > > > 'heat store/heat reserve' to 'heat resource'.
> > > > > Those individuals who could mobilise the
> > > > > sugars in their bloodstream and in various
> > > > > organs (probably converting some fats) and
> > > > > generate heat in their brains (held out of the
> > > > > water) would be able to keep their hearts
> > > > > going for longer. The larger brains would
> > > > > be like having a larger engine in a vehicle.
> > > > > Of course, the fuel will always run out in
> > > > > the end, but this is an emergency and those
> > > > > who can keep their hearts warmer more
> > > > > effectively and for longer, will do better.
> > > > N/A.
> > > > Unlike many taxa, humans defend themselves best when grouped defensively, and worse when not, this is shared with chimps.
> > > > > Elephants also have huge brains -- much
> > > > > larger than is apparently fitting for their
> > > > > body size. They are great swimmers --
> > > > > often in estuaries and cold ocean water.
> > > > > While their size provides some protection,
> > > > > the cold will get to them in long-distance
> > > > > swims. Their large brains may well function
> > > > > in the same way as I'm proposing for
> > > > > hominins.
> > > > N/A. Note that elephants do not eat seafood.
> > > > > The brains of Polar bears (498 g) are more
> > > > > than double the size of those of Grizzlies
> > > > > (234 g) -- probably the result of their having
> > > > > to swim long distances in very cold water.
> > > > > https://faculty.washington.edu/chudler/facts.html
> > > > Polar bears are much larger than grizzly bears, and are fully covered in fur.
> > > > > Polar bears evolved from brown bears relatively
> > > > > recenltly:
> > > > >
> > > > > " . . Approximately 125,000 years ago a population of brown bears
> > > > > in the far north of their range was likely split off from their brown
> > > > > bear ancestors, perhaps because of competition for food. . . "
> > > > > https://www.pbs.org/wnet/nature/arctic-bears-how-grizzlies-evolved-into-polar-bears/777/
> > > Warm blooded fauna increased specialized neuron density
> > > https://archaeologynewsnetwork.blogspot.com/2022/03/neuron-counts-reveal-brain-complexity.html?m=1
> > > See graph.
> > >
> > > Mitochondria aren't mentioned but obviously are key to faster better cognition processing. Overheating must be avoided, thus the advantage of coil-hair scalp/brain covering lofted above melanin-rich skin in tropical climes, as well as shelters.
> > -
> > Mitochondria
> > Jean Gibbons at Quora:
> >
> > How do you move energy through your body?
> >
> > ATP is formed at the mitochondria and functions as the “energy currency” within the body. Energy is found “stored” in the bonding of a third phosphate group to the molecule. Energy is contained within each and every bond, but the energy in the bonding of the third phosphate is available in a controlled fashion. ATP = Adenine TriPhosphate molecule
> >
> > The products of digestion: amino acids, glucose, fats, etc. all contain potential energy. As these chemicals are metabolized, the energy contained within is captured within a molecule of ATP.
> >
> > As the blood flows throughout the body, the energy is made available throughout as well
> https://www.sciencedaily.com/releases/2004/01/040114075853.htm

Circadian rhythm & brown fat

How circadian rhythms underlie energy production in the 'good form of fat'
September 9, 2019 by Delthia Ricks, Medical Xpress
Brown adipose tissue in a woman shown in a PET/CT exam. Credit: Public Domain

Circadian rhythms orchestrate a vast number of life's processes through the activity of a 24-hour internal clock: hormone flow, blood pressure, sleep and wake cycles, and even the timing of hibernation among marmots and bears, are controlled by a biological timepiece.

At the University of Pennsylvania, a team of scientists has been exploring the circadian clock and its relationship to brown adipose tissue, the so-called "good" form of fat. The team has uncovered the molecular underpinnings that explain how this type of fat has a chronobiological—circadian—role in the activity of brown fat, a dynamic type of tissue that provides energy through a heat-generating process called thermogenesis.

In humans brown fat is associated with being lean. In mice, rats and hibernating species, it's often linked with survival.

Reporting in a recent issue of PNAS, Marine Adlanmerinia, Mitchell Lazar and a team of scientists at UPenn's Institute for Diabetes, Obesity and Metabolism, examined the circadian nature of brown adipose fat tissue (BAT) in mice that were exposed to an exceptionally cold temperature for several days..

"Regulation of body temperature in response to cold environments is controlled by thermogenic brown adipose tissue, particularly in rodents, although it is increasingly clear that humans have functional brown adipocytes," reported Adlanmerinia and her team.

Among humans and other mammals, BAT is one of two types of fat; the other is white adipose tissue, or WAT. In humans, WAT, the type of fat associated with big rumps and beer bellies, fuels a global obesity epidemic. BAT, on the other hand, is not as common among people as it is in other species, particularly rodents. In people, BAT diminishes with age.

Babies have a high distribution of BAT compared with adults, and infants do not shiver when they are cold. They depend, instead, on thermogenesis, heat production from brown fat to keep them warm. The act of shivering in adults—shivering thermogenesis—increases body heat.

In humans, BAT is usually found in the nape of the neck and guarding vital organs, such as the kidneys. Although adults have a lower distribution of BAT than babies, people who are obese have even less BAT than those who are lean. It is theorized by some experts who study BAT that brown fat may help maintain leaness. By comparison, a range of studies over the years has shown that mice with ample BAT reserves are protected from obesity.

In the UPenn research, mice were subjected for to a temperature of 4 degrees Celsius, or 39.2 degrees Fahrenheit, for a week. The team showed how circadian-driven fat synthesis in brown adipose tissue maintained a healthy body temperature in the test mice.

Adlanmerinia and colleagues also identified genes controlling de novo lipogenesis, brown fat formation that was triggered anew to protect the animals from chronic cold during the experiment. The scientists noted "high-amplitude circadian rhythms in thermogenic BAT."

"We demonstrate that chronic cold temperature causes new circadian rhythms of de novo lipogenesis in brown adipose tissue," Adlanmerinia and the team wrote in the journal.

BAT differs from white fat not only because it responds to cold temperatures, but because it is also chock-full of mitochondria, the energy-production powerhouses of cells. The bean-shaped mitochondria cells, which have two membranes, also have a high concentration of thermogenin, a heat-generating protein, in the second membrane.

Experiments similar to the UPenn research have shown that when BAT increases in mice and other rodents, the animals are better-armed to withstand cold..

More information: Marine Adlanmerini et al. Circadian lipid synthesis in brown fat maintains murine body temperature during chronic cold, Proceedings of the National Academy of Sciences (2019). DOI: 10.1073/pnas.1909883116

Journal information: Proceedings of the National Academy of Sciences

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