The things that intrigue me most about the human body.

[CharonY]

You have to look out for migrating cells with flip charts. They are almost impossible to get rid of and cause inflammation responses everywhere.

[iNow]

And they never erase their whiteboards

[Sensei]

5 hours ago, iNow said:

And they never erase their whiteboards

True. Cells have a lot of ancient, useless junk in their DNA to these days..

 

ps. You have no idea how hard it is to erase a whiteboard I have not erased for 20 years..

 

 

Edited December 17, 2022 by Sensei

[swansont]

I’ve heard that black coffee can erase stubborn marks on a whiteboard. Of course, you have to wash the coffee residue off when you’re done.

[CharonY]

45 minutes ago, swansont said:

I’ve heard that black coffee can erase stubborn marks on a whiteboard. Of course, you have to wash the coffee residue off when you’re done.

I am not sure whether I understood the instructions, but I am licking coffee from the whiteboard now.

[swansont]

28 minutes ago, CharonY said:

I am not sure whether I understood the instructions, but I am licking coffee from the whiteboard now.

Whatever works

[TheVat]

1 hour ago, CharonY said:

I am not sure whether I understood the instructions, but I am licking coffee from the whiteboard now.

You think you are joking...but when I gave up coffee (dealing with an inner ear issue that caffeine worsens) I came pretty close to that.

Which reminds me, veering back to topic, how remarkable I find directional hearing.  Quite a neat trick of our acoustic wiring, given the small distance between our two ears.

[joigus]

On 12/16/2022 at 4:27 PM, CharonY said:

In human fossils significant bran growth was seen around 2 million years ago. While cooking would be difficult to pinpoint as the relevant factor, a study in 2004 (Stedman, H., Kozyak, B., Nelson, A. et al. Myosin gene mutation correlates with anatomical changes in the human lineage. Nature 428, 415–418 (2004)  https://doi.org/10.1038/nature0235) has found a mutation in a gene that leads to weaker jaw muscles, estimated to have occurred about 2.4 million years ago. In related primates, the jaw muscles are connected to large skull crests, which are absent from modern humans. Thus, the author speculate that when our jaw muscles stopped putting stress on the skull, the crests were not important anymore and might have opened the way to further skull growth. However, it has also been argued that some fossils still showed small brain sizes as recent as 1.8 million years ago (early Homo erectus). 

Now I don't know much about the consensus in terms of first fire use, but using wiki a range of 1.7 - 2 million years ago are mentioned. While the evidence from that time does not seem definite, it would line up with the fossil data for brain growth and myosin gene mutation. It does appear that fire use 1 million years ago is rather certain, so if we used this time point the largest discrepancy between fire use and brain growth would be around 1 million years ago (though certainly not millions).

I have also read that folks speculate that beyond cooking meat, the simple act of pre-processing food (e.g. mashing and cutting) could have contributed to the lack of need of large jaw muscles and such tools were around since at least 2.6 million years. 

 

You don't want to be bitten by a gorilla:

The thing that intrigues me the most about the human body is our loss of hair* in comparison to most other mammals. I have a vested interest on advances in this particular field of research, but still...

*Mighty selective --and peculiarly so-- as to certain body areas, especially for aging human males, I must say.

[zapatos]

22 minutes ago, joigus said:

*Mighty selective --and peculiarly so-- as to certain body areas, especially for aging human males, I must say.

I believe dachshunds and greyhounds also suffer pattern baldness.

[joigus]

2 minutes ago, zapatos said:

I believe dachshunds and greyhounds also suffer pattern baldness.

Interesting... Coincidence?

Perhaps these poor things have been too long among us.

As nothing but a guess, but a relatively learned one, the longer you live, the more wild variation not based on the common adaptive theme is bound to appear. Perhaps animals that live much longer than their expectations in the wild should be considered as natural targets for some surprises in the development of their bodies.

[MigL]

What a relief.
I thought for sure some perv was going to mention 'boobs'.

[Sensei]

7 hours ago, swansont said:

I’ve heard that black coffee can erase stubborn marks on a whiteboard. Of course, you have to wash the coffee residue off when you’re done.

Thanks for an idea.

A month ago I bought a great whiteboard for.. 5 dollars.. Which cost. 295 dollars when it was brand new..

The employer at the scrap yard wanted to destroy it and extract the metal from it (it is magnetic).

Edited December 17, 2022 by Sensei

[Ken Fabian]

7 hours ago, joigus said:

The thing that intrigues me the most about the human body is our loss of hair* in comparison to most other mammals.

And I'm intrigued by the evolution of a significant gain in sensory sensitivity in humans via those changes to patterns of hair growth. Enough to wish I could write something publishworthy about it. 

Having small hairs means it takes less to disturb them. Being effectively sparse - hairs not laid against each other - means there is less dampening of their movement should something deflect or vibrate the hair shafts.

That was my initial thinking for why my body hairs seemed so especially sensitive - able to feel the air vibrations off a fly that does a close pass, without any physical contact. Or to notice an Australian Paralysis Tick bumping hairs on it's way up my leg, enough look and pick it off before it dug in. Anyone who said body hairs serve no useful purpose hasn't avoided the painfully itchy bites of an Australian Paralysis Tick. Clearly not 100% effective, but there's that ability to get so deep in concentrated thought as to ignore our senses; maybe our ancient ancestors paid more attention.

On the other hand having very sensitive hairs make busy, buzzy flies almost unbearable; they prompt humans to take significant actions, besides swipe and swat and swear. Anything that can provoke children to screams of "get it off me, get it off me!" is not a functionless leftover. As an aside - or even more aside - I even wonder if the most common sensations hairs make being irritation is a subconscious part of the appeal of body hair removal.

It was a few years before I encountered William Montagna's "Evolution of Human Skin" and learned that human hair follicles, no matter where or how small, are especially rich with nerves in comparison to the hairs of other extant apes - more like the vibrissa, the dedicated feeler hairs than their ordinary hairs -

Quote

 

Thus, every hair in human skin, even the very small ones, functions like a vibrissa. This fact emphasizes the high degree of sensory acuity in human skin; most scientists interested in cutaneous innervation are either not aware of this fact or have ignored it even as we have stated that the nerves around our hair follicles are the anatomical base of touching, the most highly developed human sense.

 

If nothing else, this seems relevant to any ecto-parasite hypothesis for how we got the particular patterns of hair growth that humans do.

[joigus]

6 hours ago, Ken Fabian said:

And I'm intrigued by the evolution of a significant gain in sensory sensitivity in humans via those changes to patterns of hair growth. Enough to wish I could write something publishworthy about it. 

Having small hairs means it takes less to disturb them. Being effectively sparse - hairs not laid against each other - means there is less dampening of their movement should something deflect or vibrate the hair shafts.

That was my initial thinking for why my body hairs seemed so especially sensitive - able to feel the air vibrations off a fly that does a close pass, without any physical contact. Or to notice an Australian Paralysis Tick bumping hairs on it's way up my leg, enough look and pick it off before it dug in. Anyone who said body hairs serve no useful purpose hasn't avoided the painfully itchy bites of an Australian Paralysis Tick. Clearly not 100% effective, but there's that ability to get so deep in concentrated thought as to ignore our senses; maybe our ancient ancestors paid more attention.

On the other hand having very sensitive hairs make busy, buzzy flies almost unbearable; they prompt humans to take significant actions, besides swipe and swat and swear. Anything that can provoke children to screams of "get it off me, get it off me!" is not a functionless leftover. As an aside - or even more aside - I even wonder if the most common sensations hairs make being irritation is a subconscious part of the appeal of body hair removal.

It was a few years before I encountered William Montagna's "Evolution of Human Skin" and learned that human hair follicles, no matter where or how small, are especially rich with nerves in comparison to the hairs of other extant apes - more like the vibrissa, the dedicated feeler hairs than their ordinary hairs -

If nothing else, this seems relevant to any ecto-parasite hypothesis for how we got the particular patterns of hair growth that humans do.

Definitely the most interesting differential change in humans, up there along with changes in frontal cortex and trapezoid, is skin, along with its hair follicles, and how body fat is organised. I know it's been hypothesised that it's an adaptation to persistance hunting, and "managing of sweat" as a cooling mechanism, to make it possible.

In my mind, it makes evolutionary sense to put the hairs to good use as a sensory device, if you're gonna lose a lot of them for some other "collateral" reason. What I mean is several innovative features "helping each other out in a common suite of adaptive advantages" rather than one of them being the only driving causal force. Does that make sense to you?

[TheVat]

14 hours ago, Ken Fabian said:

That was my initial thinking for why my body hairs seemed so especially sensitive - able to feel the air vibrations off a fly that does a close pass, without any physical contact. Or to notice an Australian Paralysis Tick bumping hairs on it's way up my leg, enough look and pick it off before it dug in. Anyone who said body hairs serve no useful purpose hasn't avoided the painfully itchy bites of an Australian Paralysis Tick. Clearly not 100% effective, but there's that ability to get so deep in concentrated thought as to ignore our senses; maybe our ancient ancestors paid more attention.

The popular name of that tick seems well-crafted, in getting people vigilant to its possible appearance.  I wonder if the greater sensitivity is what SJ Gould called a "spandrel," something that was not initially driven by adaptive needs and was not itself selected for.  I.e. the selection process of losing bigger hairs was driven by better heat dissipation during running after game, and the creepy-crawly sensing was a spinoff byproduct that was not itself selected for but, as Gould et al noted, could later prove to be advantageous to fitness.  

 

Population migration could play a role in this.  A band of humans lives in a savannah where mosquitos and ticks were not much problem (either few, or the particular species are harmless nuisance, and do not decrease reproductive prospects) but it's quite hot.  So follicles shrink and produce tinier hairs to help handle the heat, and the sensing enhancement is a Gould-ian spandrel.  However, later migration into forests where ticks etc are dangerous, turns the spandrel into part of the suite of adaptive advantages.

[joigus]

1 hour ago, TheVat said:

Population migration could play a role in this.  A band of humans lives in a savannah where mosquitos and ticks were not much problem (either few, or the particular species are harmless nuisance, and do not decrease reproductive prospects) but it's quite hot.  So follicles shrink and produce tinier hairs to help handle the heat, and the sensing enhancement is a Gould-ian spandrel.  However, later migration into forests where ticks etc are dangerous, turns the spandrel into part of the suite of adaptive advantages.

What's very interesting is that hair loss is universal in all human families, irrespective of environment. It could have been a spandrel that got carried along because humans started using animal pelts, so there was no adaptive pressure on having more and thicker hair. If you go to the tundra you still got mammoth! If it further affords you the possibility of turning them into a sensory device for ticks, that would be very welcome.

Some further thoughts... I'm acting like a sounding board to people that know much more about this. But I love the discussion.

[Ken Fabian]

9 hours ago, joigus said:

several innovative features "helping each other out in a common suite of adaptive advantages" rather than one of them being the only driving causal force. Does that make sense to you?

Yes, I am inclined to think that there were times and circumstances where being able to keep going in hot conditions would be significant and other times and circumstances where having reduced exposure to parasites would be significant. I don't think it will be down to any one thing except perhaps the presence of a furless mutant variant at the right time.

2 hours ago, TheVat said:

I wonder if the greater sensitivity is what SJ Gould called a "spandrel," something that was not initially driven by adaptive needs and was not itself selected for.  I.e. the selection process of losing bigger hairs was driven by better heat dissipation during running after game, and the creepy-crawly sensing was a spinoff byproduct that was not itself selected for but, as Gould et al noted, could later prove to be advantageous to fitness.  

But then it could be the other way around - that body hairs staying small was driven by parasite - and parasite borne disease - avoidance and the increase in sweat glands came later and turned it into a significant heat dissipation advantage. Susceptibility to extant parasite borne disease and the presence of mutations that reduces it would have a very strong selective effect, even within a single generation; the furless mutant types, despite the problems - with the problem solving, tool using capacity to work around the problems

[Genady]

3 minutes ago, joigus said:

What's very interesting is that hair loss is universal in all human families, irrespective of environment. It could have been a spandrel that got carried along because humans started using animal pelts, so there was no adaptive pressure on having more and thicker hair. If you go to the tundra you still got mammoth! If it further affords you the possibility of turning them into a sensory device for ticks, that would be very welcome.

Some further thoughts... I'm acting like a sounding board to people that know much more about this. But I love the discussion.

Interestingly, peoples who started putting on clothes thousands of years ago, East of Mediterranean, have more bodily hair today than peoples who didn't cover their bodies until recently, Australian, African, Amazonian tribes. (My personal observation.)

[Ken Fabian]

50 minutes ago, Genady said:

Interestingly, peoples who started putting on clothes thousands of years ago, East of Mediterranean, have more bodily hair today than peoples who didn't cover their bodies until recently, Australian, African, Amazonian tribes. (My personal observation.)

Only the adults have more (as in larger) body hairs. The children are as furless as children everywhere else. I think that is a significant observation that has been largely overlooked in developing plausible explanations for how we got to be a furless ape. It tells us that greater adult hairiness within some groups must have evolved later than the childhood furlessness that is universal across our species.

All the variations of hairiness in adults, barring perhaps some dimorphic (male vs female) differences, would have arisen after speciation.

If I could write academic style papers I would address this, along with the sensory function of hairs - "hairlessness" itself is in my view better framed conceptually as a developmental trait and might be better described as a furless childhood condition than as a species with furless adults. Which means any hypothesis for childhood furlessness based on sexual selection has serious problems; how does choosing a less hairy adult mate lead to children having no fur? The childhood furlessness has to pre-exist for sexual selection to be able choose less hairiness in adult mates.

Edited December 18, 2022 by Ken Fabian

[mistermack]

I think the persistence hunt hypothesis is one of the more way-out hypotheses about human evolution, a bit like the aquatic ape. People get fixated on the notion, and start interpreting everything one way, towards the desired story. 

I saw the David Attenboro documentary that featured it, and some of the claims made were ridiculous. And tellingly, he also pushed the aquatic ape notion when he had the chance. 

The San hunters in his film were all wearing modern trainers, and carrying plastic water bottles. Why wouldn't they? And even with those aids, there was only one man who could actually run down the Kudu. And I was a bit suspicious of how that was done for the film. https://www.youtube.com/watch?v=826HMLoiE_o

 

But anyway, take away the shoes, and let's see them run down a Kudu. In reality, the peristence element of hunting probably just involved walking down an injured animal, and that probably came very late in our history, after the invention of the throwing spear. Wound an animal, and then follow the trail of blood and tracks. No need to run. 

I think it's most likely that the sweat glands evolved after and because we lost our fur coat. No point in evolving new sweat glands, if the evaporation is restricted by hair. The sweat will just drip off the fur. But once the fur has gone, then the sweat glands could bestow a real benefit. 

Losing the fur I believe was down to building shelters, and carrying skin cloaks. Why does a Chimp need fur? Not for normal daytime keeping warm. It's for cold wet nights. Same as most animals in hot countries. The fur stops rain contacting the skin, so it's some protection against sudden chills in a downpour, or cold wet nights. Humans started making shelters and carrying skins, so they got the protection against the worst weather. Then, when the sun comes out, they came out from the shelter, threw off the cloak, and had no need at all for a covering of hair. So the benefit of losing the hair was better cooling, and also less hair for parasites to cling to.

Once you have replaced the benefits of fur with shelters and skins, you are just left with the drawbacks, so the coat of fur disappeard over time. 

[CharonY]

It is a bit funny to start with valid criticism, but then falling into the pit of, well, making things up. For example, if loss of hair was due to the wearing skin cloaks, then why did our presumably hairy ancestors start with that practice in the first place? How would they prepare skins to wear and is there any evidence to that end? I doubt that they would just wrap themselves in putrefying carcass (at least non of our cousins are doing it).

 

 

 

[Lorentz Jr]

13 minutes ago, CharonY said:

It is a bit funny to start with valid criticism, but then falling into the pit of, well, making things up. For example, if loss of hair was due to the wearing skin cloaks, then why did our presumably hairy ancestors start with that practice in the first place?

Clothing over smooth skin (A) is better than clothing over hairy skin (B).

Clothing over hairy skin is better than no clothing at all (C).

Not saying that's true, but A>B doesn't disprove B>C.

Edited December 18, 2022 by Lorentz Jr

[mistermack]

23 minutes ago, Lorentz Jr said:

Clothing over hairy skin is better than no clothing at all (C).

True. Even an Orangutan can work that out. 😄 

 

 

[Ken Fabian]

 

2 hours ago, mistermack said:

Losing the fur I believe was down to building shelters, and carrying skin cloaks.

It seems more likely to me that use of clothing was a response to being furless rather than inducing furlessness - a parental response to their furless children suffering from cold perhaps. It is certainly possible the use of clothing and shelter and fire came before the loss of fur and gain in sensory sensitivity but I don't see how it would lead to evolving furless children. I have dogs that are very pleased to wear warm jackets in winter but I don't expect dogs to evolve furlessness as a consequence. 

There has been more going on than reduced hair size. Skin has gotten tougher and makes more perspiration and gained (variably) resistance to UV. Hairs gained sensory sensitivity. Seems unlikely they happened simultaneously or for the same reason.

2 hours ago, mistermack said:

But anyway, take away the shoes, and let's see them run down a Kudu.

Abebe Bikila famously won back to back Olympic Marathons with bare feet. I don't see any fundamental problem with running long distances without shoes. Australian desert Aboriginals traveled long distances in harsh conditions without footwear but I'm not aware of persistence hunting as a usual hunting method. Sneaking up on prey and using spears or hunting boomarangs seems more usual. Chasing down wounded prey no doubt happened - but I expect marksmanship would be criticised; a few times and young hunters would learn the worth of taking prey down quickly, to avoid all that chasing after them.

African Bushmen however, are noted for long distance running and persistence hunting - the Kalihari Desert is a unique and challenging environment. More usually a variety of hunting methods were used, from snares and traps to ambushes at water holes or river crossings (which the Kalihari doesn't have).

But I also have some reservations about reliance on persistence hunting of large prey as the primary source of high protein food, but conceivably at some extreme bottleneck - where the very survival of the species was in doubt such as due to extreme anf persistent drought - it may have been so... if an ability to sweat profusely had already developed and overlapped with individuals having loss of fur. There are some furry primates that sweat a lot.

[joigus]

The question seems far from being settled. I've just found this interesting article:

https://www.smithsonianmag.com/science-nature/why-did-humans-evolve-lose-fur-180970980/

Some of the hypotheses seem a bit far-fetched to me. Let go of you fur because you are better able to notice other people blushing? It seems a tad extreme.

A protein seems to be involved that apparently acts as an inhibitor to selectively suppress hair growth in certain areas. In most mammals --according to the article-- the difference manifests itself in the plantar skin in some exceptional mammals --polar bears and some rabbits. Maybe for humans there are intensifiers at the level of regulatory sequences or the like? But there must be a strong evolutionary pressure behind it.

Another interesting piece of information providing likely timeline:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3002236/

The main argument is about when clothing probably appeared based on evolutionary divergence of head/clothing lice.