Understanding through Discussion


Welcome! You are not logged in. [ Login ]
EvC Forum active members: 115 (8796 total)
Current session began: 
Page Loaded: 10-20-2017 1:53 PM
367 online now:
Aussie, DrJones*, foreveryoung, Joe T, PaulK, Percy (Admin), ringo, Tangle, xongsmith (9 members, 358 visitors)
Chatting now:  Chat room empty
Newest Member: jaufre
Upcoming Birthdays: Flyer75
Happy Birthday: Astrophile
Post Volume:
Total: 820,913 Year: 25,519/21,208 Month: 1,146/2,338 Week: 267/450 Day: 32/55 Hour: 3/3

Announcements: Reporting debate problems OR discussing moderation actions/inactions


Thread  Details

Email This Thread
Newer Topic | Older Topic
  
Prev1234
5
6789Next
Author Topic:   Sexual Selection, Stasis, Runaway Selection, Dimorphism, & Human Evolution
EZscience
Member (Idle past 2712 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 61 of 131 (212647)
05-30-2005 1:28 PM
Reply to: Message 60 by RAZD
05-28-2005 10:31 AM


Selected genes and polymorphisms.
RazD writes:

The other positively selected mutations on the X gene though -- they don't talk to much about them, would they likely be {ones\areas} more related to females?

Not necessarily. Remember, many genes on the 'X' chromasome serve important functions in both sexes, and many genes for 'female' traits are located on other chromasomes - there are just not expressed to the same degree in males. I like to think of it this way. ALL genes have to survive in BOTH sexes (in an obligately sexual population), and most serve some function in both. The differences in 'gender' that seem so pronounced to us in the final phenotype are mostly just the result of subtle changes in degree of expression of the same genes at particular times in development. I expect Wounded King could elaborate further on this if he were around.

With regard to the apparent deficiency of polymorphisms observed at some loci, the observation is significant because of the number of apparent changes (base substitutions) that have occurred in these loci. Lack of polymorphism implies that, of many possible versions of the gene that did occur, only one was 'tolerable' for that lineage. Strong evidence for selection driving the fixation, otherwise where are all the other variants of the gene that had to come into existence at some point?


This message is a reply to:
 Message 60 by RAZD, posted 05-28-2005 10:31 AM RAZD has responded

Replies to this message:
 Message 62 by RAZD, posted 05-30-2005 2:24 PM EZscience has not yet responded
 Message 63 by sfs, posted 05-30-2005 10:40 PM EZscience has responded

  
RAZD
Member
Posts: 19089
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5


Message 62 of 131 (212659)
05-30-2005 2:24 PM
Reply to: Message 61 by EZscience
05-30-2005 1:28 PM


Re: Selected genes and polymorphisms.
yes. I am aware that the absence of testosterone during development of a genetically male child causes the individual to grow up for all intents and appearances as a female, just absent the uterus and internal female organs (the testes never descend).
This message is a reply to:
 Message 61 by EZscience, posted 05-30-2005 1:28 PM EZscience has not yet responded

  
sfs
Member (Idle past 92 days)
Posts: 464
From: Cambridge, MA USA
Joined: 08-27-2003


Message 63 of 131 (212740)
05-30-2005 10:40 PM
Reply to: Message 61 by EZscience
05-30-2005 1:28 PM


Re: Selected genes and polymorphisms.
quote:
With regard to the apparent deficiency of polymorphisms observed at some loci, the observation is significant because of the number of apparent changes (base substitutions) that have occurred in these loci. Lack of polymorphism implies that, of many possible versions of the gene that did occur, only one was 'tolerable' for that lineage. Strong evidence for selection driving the fixation, otherwise where are all the other variants of the gene that had to come into existence at some point?

The lack of polymorphism does not indicate anything about mutations that occurred but that are not seen as polymorphisms. It is evidence for a selective sweep, in which a mutation at one site brings to fixation any nearby alleles on the particular chromosome on which the favorable mutation occurred.

I also want to digest this paper for a while -- there are some surprising features in their results.


This message is a reply to:
 Message 61 by EZscience, posted 05-30-2005 1:28 PM EZscience has responded

Replies to this message:
 Message 64 by EZscience, posted 05-31-2005 7:16 AM sfs has not yet responded

    
EZscience
Member (Idle past 2712 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 64 of 131 (212781)
05-31-2005 7:16 AM
Reply to: Message 63 by sfs
05-30-2005 10:40 PM


Re: Selected genes and polymorphisms.
I stand corrected.
I was unfamiliar with the term 'selective sweep'.
This message is a reply to:
 Message 63 by sfs, posted 05-30-2005 10:40 PM sfs has not yet responded

Replies to this message:
 Message 66 by RAZD, posted 06-02-2005 9:15 PM EZscience has not yet responded

  
RAZD
Member
Posts: 19089
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5


Message 65 of 131 (213411)
06-02-2005 7:47 AM
Reply to: Message 1 by RAZD
04-23-2005 6:13 PM


ADDENDUM II

Enabling Mechanisms

The loss of long thick colorful terminal hair, typical of other apes, in favor of short thin pale vellus hair, as found on most of the human body skin areas, means that the insulation value of that hair has been lost. This insulation protects the individual from both heat and cold, modulating the extremes to provide a more constant "microclimate" for the individual. The loss of such insulation would leave the individual subject to both greater heat gain and greater heat loss without some other mechanism(s) to counteract these trends.

If anyone doubts the ability of insulation to provide sufficient protection from too much heat, then consider that Arabs in the Sahara Desert wear clothes that essentially replace this function of fur - from head to toe.

This is not just the {elongation\oversizing} of {decorative\sex-competitive} features, like tails or antlers, which develop until they reach a point of jeopardizing survival, but the alteration of a feature basic to survival from the start - and in a direction, and to an extreme, that could easily affect survival adversely. The loss of hair presents two simultaneous problems:

Too much exertion on a windless hot sunny day: in the absence of any mechanism to {shield\protect\divest} a body of excess heat, hyperthermia becomes a foregone conclusion, and likely to be fatal if no counteraction is taken. This happens to humans who lose the ability to sweat (or have maxed out their sweat-ability - more below). See Wikipedia - Hyperthermia (click):

Body temperatures above 40C (104F) are considered life-threatening. At 41 C (106 F), brain death begins, and at 45C (113 F) death is nearly certain. Internal temperatures above 50 C (122 F) will cause rigidity in the muscles and, therefore, certain immediate death.
Signs include increasing body temperature (hyperpyrexia), dehydration and lack of sweating, seizures, collapse and decreased consciousness which proceeds rapidly to multi-organ failure and death as the brain 'cooks'.

On the opposite side is the problem of surviving cold windy rainy nights, with activity at a minimum, for then hypothermia becomes a foregone conclusion. This happens to humans that get wet when it is cool and windy. See Wikipedia - Hypothermia (click):

If body temperature falls below 32 C (90 F), the condition can become critical and eventually fatal. Body temperatures below 27 C (80 F) are almost uniformly fatal, though body temperatures as low as 14 C (57.5 F) have been survived.

If you've ever had your skin turn blue with goose-bumps and your teeth chatter when swimming on a summer day, you've experienced hypothermia (and "goose-bumps" are the retained muscle reaction to cold which made the body hairs stand on end to increase insulation value).

From 90 F to 104F is a pretty narrow window for acceptable body temperatures. With a loss of thermal regulation, the results could quickly be fatal unless the development occurred over time and there were enabling mechanisms to allow for a more incremental development of {apparent bareness} in humans.

You can think of this as the "goldilocks problem" - not too hot and not too cold, but just right.

Environment: the Serengeti area in Tanzania, home to Olduvai Gorge, is thought to be one of the ranges of early {hominids\humans}, and from The Serengeti National Park (click)

With altitudes ranging from 920 to 1,850 metres - higher than most of Europe - mean temperatures vary from 15 degrees to 25 degrees Celsius. It is coldest from June to October, particularly in the evenings.

That's 60F to 75 (F59F to 77F), and the "rainy season" lasts for months. Those temps are the means. From Kenya Country Information (click):

Extreme temperatures in Nairobi range from 50 degrees to 90 degrees.

In a forested environment those extreme temperatures would be moderated, but the thing to note is that these are all below the normal human body temperature, and at their highest reach the lower limit of concern for human body temperature.

Current anthropological thinking is that humans developed the fully bipedal gait some 5- 6 million years ago, while still living in a forested environment:

From African Continental Paleoclimate and Hominid Evolution II (click):

Our glacial simulations indicate that tropical broadleaf forest was not severely displaced by grassland expanding into central Africa, although the outer extent of closed forest decreases, particularly in the north. Our vegetation-climate simulations also indicate that the extent of closed tropical forest during typical interglacials is not represented by today's observed vegetation distributions. Simulated interglacial climate results in expansion of tropical forest from coast-to-coast across much of central Africa.

And from Soil Suggests Early Humans Lived In Forests Instead Of Grasslands (click):

The analysis was of fossil soils from paleontological sites in the Middle Awash region of Ethiopias rift valley, where the remains of a new subspecies of Ardipithecus ramidus have been discovered. They date to the late Miocene period (5.4 million to 5.8 million years ago). Scientists from four institutions report their findings in a pair of papers that appear in the July 12 issue of the journal Nature.
The region where the fossils were found is now a hot, dry semi-desert occupied by nomadic camel herders. At the time the area formed, it was higher in elevation, cooler, wetter and more forested.
The nodules from these late-Miocene hominid fossil sites contain low levels of carbon 13, which is consistent with trees and woody plants. They also contain oxygen isotope ratios that are indicative of a cool, humid climate. "These hominids were living in the forest, despite the fact that grasslands were available," Ambrose said.

Given this environment, substantial {apparent bareness} could develop without jeopardizing survival through overheating. This would indicate that the primary concern in this environment would be to prevent heat loss rather than getting too hot, at least during the initial stages.

A cool shaded environment enables the development of bareness while only having to provide alternate heat retention mechanisms, and not have to provide both retention and dissipation.

Heat Retention: from Human Thermoregulation and Hair Loss (click)

The human vascular system has developed reactions to both heat stress and cold stress. The skin has a system of thermal receptors that perceive temperature of the skin and send signals carrying this information to the autonomous nervous system. When the body perceives increased heat loss through the skin, vasoconstriction of the peripheral vascular system occurs to decrease the blood flow (which carries heat from the core to the surface). In humans this vasoconstriction can reduce heat loss by 1/6 to 1/3 depending on the individual and the acclimation of the individual to cold stress. When the body perceives a need for increased heat loss, vasodilation occurs, with increased blood flow to the peripheral vascular system. This vasodilation increases the rate of heat transfer from the core to the surface, and is also an important feature involved with sweating.

We'll get to sweating again later, but it seems that this vascular system would be one of the first mechanism employed, developed within it's limits to enable some level of {apparent bareness}.

The likelihood is that certain areas (breast and buttocks?) were selected for {apparent bareness}, with the rest remaining as before. This would be similar to the gorilla, with the male's "bare" chest area and the female's "bare" breasts, a degree of {apparent bareness} that does not inhibit their survival (although the gorilla has more body mass than the female human, particularly more than an early hominid would have).



(1st picture originally from http://www.bristolzoo.org.uk)
(2nd picture originally from http://www.hedweb.com/gorilfam.htm)

One advantage of the vascular system is that it works for both heat retention and cooling, thus it is best able to replace both those functions lost with hair reduction, especially for daily fluctuations where a fairly rapid response would be needed. The disadvantage is that it is not as capable of modulating extremes of heat and cold as hair would be.

Another heat retention system common to many mammals is a thicker layer of subcutaneous fat. This layer exists in all primates, but is most developed in humans. Again, from the same source on thermoregulation:

The distribution of a thick subcutaneous fat layer in modern humans is another "unique" feature in relation to closely related non-human primates, and should be considered in any theory that invokes a thermoregulatory explanation. However, this is hard to distinguish as either a true problem or a false one, as humans do not have any more points of fat production than other primates, but rather have more fat developed from these individual centers ...
Body fat is located under the dermis in a subcutaneous layer. This fat can have several functions in mammals that may or may not be related to thermoregulation. ... The development of a thick layer of subcutaneous fat may be an adaptation to the loss of body hair and the potential cold stress that the human ancestor would have experienced, or may simply be a feature of the behavioral capacity of humans to get access to food.

In the cool forested environment discussed above, absorbing too much radiant energy from the sun would not be a concern, but radiating too much energy to the environment would be. In this type of environment a thicker subcutaneous fat layer would provide sufficient insulation to enable further development of apparent bareness. This would not be fast acting (like the vascular system) but it would be adaptable to seasonal variation, with thicker fat layers in the cooler seasons, thinner in the hotter ones.

This subcutaneous fat layer is one of the arguments for the 'aquatic ape' theory, as aquatic mammals use this to insulate them from the cooler water, but it does not require an aquatic environment so much as a cooler environment. If the environment was consistently cool enough that overheating was not a problem (as the environmental evidence shows above), then the development of the subcutaneous fat layer would provide an incremental increase of insulation to replace an insulation decrease due to a further loss of hair (and still allow the vascular system to deal with day to day variations) without needing an aquatic environment to explain it.

If anyone doubts the ability of these mechanisms to provide sufficient protection from hypothermia (not too cold), then consider that when the Beagle reached the area of Tiera del Fuego at the south end of South America, that the crew were welcomed by nearly naked natives while Darwin and the others froze with the clothes they had on:

From http://geography.about.com/library/misc/uctierra.htm

On one occasion Darwin and crew were near a good size fire and still quite cold, while the aborigines were some distance away and perspiring heavily. Charles noted this with great interest.

The 'bipedal ape' theory postulates that the upright posture is a better radiator of heat while decreasing the area for absorption of heat from the sun. Other studies have disputed the thermal balance calculations, but most of these (pro and con) calculations relate to the high temperatures of a savannah environment. Again, from the (same source on thermoregulation:

A scenario that makes bipedalism a necessary pre-adaptation for the loss of body hair means that bipedalism would have occurred in the absence of the development of the sweating mechanism, and thus the heat dissipation of this proto-biped would not have had the heat dissipative capabilities of a modern human.
When this factor is accounted for, the putative greater heat load capacity of a naked skin of a newly developed biped over denser body hair is negated. Amaral (1996) showed that the thermal stress on a naked biped is up to three times greater at higher temperatures than on a hair-covered skin. In fact, this is exactly the reason that other savanna primates have a dense coat of fur that is even more developed than forest dwelling primates do.

The argument of the 'bipedal ape' theory is that heat loss is enhanced by the upright posture and that the upright posture developed on the savannah as a way to look over the tall grass. But the problems here are (1) we are still in that forest environment (2) we haven't developed the mechanism for sweating yet (3) we don't need to have cooling enhanced, and (4), the biggest problem of all, (ibid):

Sweating is a thermoregulatory mechanism of modern humans that effectively removes body heat through evaporation. It becomes extremely effective in the absence of heavy body hair, and actually can be maladaptive in the presence of heavy hair cover.
Effective sweating requires as little hair cover as possible, as it needs air contact (particularly moving air) over the skin to remove the heated sweat. In an individual with a prodigious sweating mechanism and dense hair cover, the heated sweat will generally be retained by the hair cover and actually begin to act as insulation preventing heat loss, leading to hyperthermia.

In other words, {apparent bareness} had to precede the development of sweating, and it had to happen in an environment cool enough that prevention of overheating was not critical to survival (ibid):

... but the preconditions that would favor the loss of body hair and the development of a sweating mechanism (high environmental or metabolic thermal stress relative to an earlier state) can be shown to occur prior to when hunting can be reasonable inferred as a likely possibility. A radiation of hominids circa 2 mya indicates a shift into new environments (and the capacity to survive in these environments), and an even earlier increase in body size would indicate increased metabolic stress with the expense of less efficient heat loss through convection with the air. These are events that likely would have involved the need for the development of thermoregulatory changes much earlier than any reasonable evidence of hunting.

Rather it would seem that (hyper?) development of {apparent bareness} enabled the evolution of sweating and thus allowed the bipedal savannah hunter to take the stage.

The next question is how did the mechanism of sweating evolve, and especially whether any mutation is required to enable it.

That will be addendum III

Enjoy


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}


This message is a reply to:
 Message 1 by RAZD, posted 04-23-2005 6:13 PM RAZD has acknowledged this reply

Replies to this message:
 Message 67 by EZscience, posted 06-02-2005 10:59 PM RAZD has responded

  
RAZD
Member
Posts: 19089
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5


Message 66 of 131 (213673)
06-02-2005 9:15 PM
Reply to: Message 64 by EZscience
05-31-2005 7:16 AM


Re: Selected genes and polymorphisms.
next addendum added
This message is a reply to:
 Message 64 by EZscience, posted 05-31-2005 7:16 AM EZscience has not yet responded

  
EZscience
Member (Idle past 2712 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 67 of 131 (213690)
06-02-2005 10:59 PM
Reply to: Message 65 by RAZD
06-02-2005 7:47 AM


Re: ADDENDUM II
RazD writes:

The likelihood is that certain areas (breast and buttocks?) were selected for {apparent bareness}, with the rest remaining as before.

So maybe there were advantages under SS for bare breasts and buttocks to be used in sexual signaling and communication of receptivity in females ?

RazD writes:

The next question is how did the mechanism of sweating evolve, and especially whether any mutation is required to enable it.

I follow your logic so far. Interesting that pigs are virtually bare and yet do not sweat. They are forced to compensate behaviorally by finding a mud hole to wallow in when it is hot.

So here's my shot regarding conditions for evolution of sweat glands in humans:

1. low relative humidity - no evaporative cooling takes place if the air is saturated with water (I've lived in Florida)

2. good average airflow over the body (more likely in a plains environment than in a forest)

3. lack of beahvioral compensatory mechanisms (like the pig). Once again points to an arid environment with little shade and water holes few and far between.

4. potential advantages of sweat glands as sexual signalling devices via olfaction (Ummmmm.... baby you smell gooooood).

...just off the top of my head.


This message is a reply to:
 Message 65 by RAZD, posted 06-02-2005 7:47 AM RAZD has responded

Replies to this message:
 Message 68 by RAZD, posted 06-04-2005 12:43 AM EZscience has not yet responded
 Message 69 by RAZD, posted 06-04-2005 6:18 PM EZscience has not yet responded

  
RAZD
Member
Posts: 19089
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5


Message 68 of 131 (214077)
06-04-2005 12:43 AM
Reply to: Message 67 by EZscience
06-02-2005 10:59 PM


Re: ADDENDUM II
4. sort of ... except for the pigs -- they had no eccrine glands on the skin to become sweat glands: for humans this is your typical hijacking of one sytem to become another.


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}


This message is a reply to:
 Message 67 by EZscience, posted 06-02-2005 10:59 PM EZscience has not yet responded

  
RAZD
Member
Posts: 19089
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5


Message 69 of 131 (214250)
06-04-2005 6:18 PM
Reply to: Message 67 by EZscience
06-02-2005 10:59 PM


Re: ADDENDUM II
2. good average airflow over the body (more likely in a plains environment than in a forest)

or in little islands of forest as the savannah environment grows around them -- as noted in the article on soil samples above:

"These hominids were living in the forest, despite the fact that grasslands were available," Ambrose said.

time for installment #3 ... see msg 70.

This message has been edited by RAZD, 06*04*2005 06:23 PM


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}


This message is a reply to:
 Message 67 by EZscience, posted 06-02-2005 10:59 PM EZscience has not yet responded

  
RAZD
Member
Posts: 19089
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5


Message 70 of 131 (214251)
06-04-2005 6:21 PM
Reply to: Message 1 by RAZD
04-23-2005 6:13 PM


Addendum III -- Sweat it.

Sweat

What is it, how does it work and where did it come from?

Once again, from Human Thermoregulation and Hair Loss (click)

The sweat on the surface of the skin is mostly water and has a high specific heat. Heat is removed from the skin by conduction to the sweat until the sweat is either evaporated or sloughed off. Sweating is most effective if the sweat is actually evaporated, since it is removing more heat per unit of sweat being produced.
... Eccrine glands are specialized sweat glands that produce large quantities of sweat that is mostly water ...
Vasodilation increases the blood flow from the core to the periphery while increasing the rate of heat loss to the skin, which is then removed through the evaporation of sweat ...

The vascular system opens to transfer heat to the skin (as before), Eccrine glands transfer that heat to water and transports the heated water to the skin surface, where evaporation removes heat energy, cooling the surface (which is then transmitted back to the interior by the vascular system). The system is very efficient for moving heat quickly to the surface where it then depends on evaporation to finish the cycle

Now we need to know what Eccrine glands are and how we got them. Let's continue (ibid):

The distribution of these glands along the body follows a very regular pattern. Sebaceous glands are found in association with all or nearly all hair follicles and have no known functional significance in thermoregulation. Apocrine glands are found in the axillary regions (the pubis, the perianal region, and the axillae) in humans, whereas in most non-human primates (excluding gorillas and chimpanzees) they are found throughout the entire body. It is important to note that in the human fetus apocrine glands begin to form all over the body in association with hair follicles, but are mostly resorbed into the body during development. Eccrine glands are found over the entire surface of the body, in both hairy and non-hairy areas, and have no developmental tie to individual hair follicles. In most non-human primates (again excluding gorillas and chimpanzees) eccrine glands are only found on surfaces used in locomotion (the soles of the hands and feet, and among the dermatoglyphics found on places of high friction, like the tails of prehensile species or the knuckle pads of knuckle-walkers.

The original purpose of Eccrine glands is to keep bare areas of skin (and areas likely to build up calluses) soft and supple. Note the exclusions of Chimpanzees (I assume they include Bonobos as "Pigmy" Chimpanzees) and Gorillas, our closest relatives in the ape family. This means that at some point previous to the divergence of Humans, Chimpanzees and Gorillas, a mutation (1) occurred and (2) was fixed, that caused the expression of Eccrine glands on these other body areas. Current thinking is that humans and chimpanzees shared a common ancestor some 5-6 million years ago, and that humans, chimpanzees and gorillas shared a common ancestor some 1 million years earlier:

From http://www.ecotao.com/holism/add/Hominoidea.html:

(This) yields a time and 95% confidence interval of 5.4 +/- 1.1 million years ago (36 nuclear genes) for the human-chimpanzee divergence. Older splitting events are estimated as 6.4 +/- 1.5 million years ago (gorilla, 31 genes) ...

The fact that this mutation shows up in Gorillas and Chimpanzees indicates that it was likely fixed before the selection for {apparent bareness} occurred. In humans this inherited mutation was opportunistic to the development of a new and effective (within limits) means to deal with overheating of an already {apparently bare} body, and this allowed the expansion of humans into hotter and more open environments as the forests were replaced by savannahs.

There are a couple of draw-backs to the sweating mechanism: (1) If the air is saturated with moisture, then evaporation does not happen and only the less efficient "sloughing" (sweat run-off) occurs (and if there is no air movement then the saturation can be localized, building up around the individual: hot sweaty nights); (2) There is only so much moisture in the body, and it is possible to sweat up to 2 liters of water in an hour.

From http://www.cptips.com/fluids.htm

And this is especially true in cycling where evaporative losses are significant and can go unnoticed even though sweat production and loss through the lungs can easily exceed 2 quarts per hour. To maximize your performance, it is essential that fluid replacement begin early and continue throughout a ride. A South African study comparing two groups of cyclists (one rehydrating, the other not) exercising at 90% of their maximum demonstrated a measureable difference in physical performance as early as 15 minutes into the ride.

From MARATHON PHYSIOLOGY (click)

Sweat: During a marathon, sweat production routinely ranges from 1 to 1.5 liters per hour, and can exceed 2 liters per hour for some runners. If you sweat much more than you drink on the run, your blood volume drops, reducing the amount of blood that is pumped with each heart beat. When this occurs, your heart rate increases and eventually your pace will suffer.

And without a means to replenish this water continued exertion will result in depletion of the water reserve (dehydration), and hyperthermia will ensue. In spite of copious water supplies along the route several marathon runners at the recent Greek Olympics succumbed to hyperthermia. Hair (or fur) does not need to be replenished, so this reliance on extra water for sweat can be a disadvantage in some areas.

Pheromones: Apocrine glands also produce some liquid material, and this responsible for the distinctive odors associated with sweat, odors that may be linked to pheromones, again from Human Thermoregulation and Hair Loss (click):

The sebaceous glands - as mentioned previously - act as lubricants for the skin and hair, maintaining moisture content and prevent the skin and hair from drying out and cracking. The apocrine glands in humans (and gorillas and chimpanzees) seem to have a sexual function, and produce odors. This occurs through the combination of the sebaceous, apocrine, and eccrine glands. In the axillary areas the sebaceous and apocrine glands produce a constant stream of secretions of high cellular content. When the eccrine glands are stimulated to produce sweat, the sweat mixes with the secretions of the sebaceous and apocrine glands and spreads throughout the axillary area. In the moist microenvironment of these areas, bacteria is abundant on the skin and on the hair, and when given access to the organically saturated sweat, begins to break down the cellular components, with body odor as the result of this process. The sweat excretions themselves are odorless.

When I started this essay I wondered if our sweat glands had evolved out of the pheromone producing ones, and that this conversion would explain the seeming loss of pheromones in humans. Instead what we see is that the areas that were previously covered with Apocrine glands have diminished to just the armpits and genitals and that they have been replaced by the sweat glands in the other areas, thus reducing the output and diluting it as well. And it could well be possible that the "microenvironment fauna" have evolved and so the odors are no longer similar to what they used to be. It is also possible that during the initial stages of developing sweat glands out of Eccrine glands (by increasing their output), that the early hominids were awash in pheromones and that this drove the species towards the shortened sex cycle and more universal sexual "availability" that is also a characteristic of humans (and Bonobos - those hedonistic "pygmy" Chimpanzees).

I have one more piece to the puzzle to add, but need to work on it some more.

enjoy

{edited to fix html link title}

This message has been edited by RAZD, 06*04*2005 06:27 PM


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}


This message is a reply to:
 Message 1 by RAZD, posted 04-23-2005 6:13 PM RAZD has acknowledged this reply

  
RAZD
Member
Posts: 19089
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5


Message 71 of 131 (216308)
06-11-2005 10:52 PM
Reply to: Message 1 by RAZD
04-23-2005 6:13 PM


last addendum

Final Words

The Chimpanzees and Gorillas do not have the sweating mechanism in spite of having the Eccrine glands, and this would indicate that they had too much hair for sweating to be effective (they could not simultaneously evolve less hair and sweat) and thus were stuck in the shadows of the forest. This would also mean that Human {apparent bareness} was fully developed when the savannah encroached on the forests and early hominids began to sweat, and then began to go hunting in the new environments that this adaptation allowed.

The final clue may be in a seeming side comment in this article, Humans March to a Faster Genetic "Drummer" Than Other Primates, UC Riverside Research Says (click)

A team of biochemists from UC Riverside published a paper in the June 11 issue of the Journal of Molecular Biology that gives one explanation for why humans and primates are so closely related genetically, but so clearly different biologically and intellectually.

It is an established fact that 98 percent of the DNA, or the code of life, is exactly the same between humans and chimpanzees. So the key to what it means to be human resides in that other 2 percent.

The team, which also included Rosaleen Gibbons, Lars J. Dugaiczyk, Thomas Girke, Brian Duistermars and Rita Zielinski, identified over 2,200 new human specific Alu DNA repeats that are absent from the chimpanzee and most likely other primates.

"The explosive expansion of the DNA repeats and the resulting restructuring of our genetic code may be the clue to what makes us human," Dugaiczyk said. During the same amount of time, humans accumulated more genetic novelties than chimpanzees, making the human/chimpanzee genetic distance larger than that between the chimpanzee and gorilla.


(bold added for emPHASis)

Note that the {chimp\human} ancestor diverged from the {gorilla} ancestor before the {chimp} ancestor diverged from the {human} ancestor. For there to be more mutations selected for fixation within the human genome means that either survival pressure operating on just humans, or that some process was actively selecting changes. These same changes were fixed in the human genome before humans spread around the world, from DNA variations surprise researchers (click)

Early information from the Human Genome Project indicated that the DNA in the genome of any two individuals is 99.9 per cent identical with the 0.1 per cent variation arising primarily from some three million single nucleotide changes scattered amongst the chromosomes. The new data from the Sick Kids and Harvard groups revealed 255 regions (comprising more than 0.1 per cent) of the genome where large chunks of DNA are present in different copy numbers between individuals ...

So all but ~0.25% of the current genome is shared by all humans, and (neglecting mutations since dispersal) that of the 2% difference between humans and chimps ~85% therefore must have been fixed in the genome before the first bipedal foot left Africa, ~200,000 years ago.

I fully expect most of those Alu repeats to be associated with those {feature\characteristics} where we have a measurable quantitative (more\less of) rather than qualitative (type of) difference: brain size, breast size, buttocks size, penis size, sweat, head hair, bareness.

While the mechanism of run-away sexual selection may be debated for some of these features, this certainly would provide an undeniably active selection mechanism that would result in a genetic pattern similar to that found.

Conclusions

Apparent bareness had to evolve before sweating could evolve, and it could only evolve while early hominids did not need protection from sever heat stress: while the tropical forest cover was their chosen habitat.

Sweating had to evolve before humans could venture far into the savannah environment in order to deal with the sever heat stress of living in that environment without the protection of {fur\hair}: while the forest was being replaced with savannah but still provided refuge during times of peak heat stress.

Apparent bareness and other features show signs of run-away sexual selection; the genetic code shows sign of active selection at a rate higher than normal natural selection, thus reinforcing the (circumstantial) evidence for sexual selection having been an active mechanism in human evolution.

While such an evolutionary process may include specific {feature\direction} aspects, it certainly was not random evolution, but it also certainly was not free of random circumstances (change in climate, change in environment). The actual process was enabled by the ecological conditions that prevailed and by genetic mutations that could be tuned to suit the {sexual\selected} needs, but those {mutations\features} needed to already be available to be acted on. This is the way that selection interacts with variation to produce change in species over time.

I also like to think those early hominids had developed one final enabling mechanism that allowed the further spread of the {apparently bare} ape into the world at large: portable shelter, replacement hair, ... proto-clothes. Perhaps capes made of woven grasses or disguises cut from the hides of opportunistic finds. Thus a naked species moves out from a diminishing subtropical garden forest into a hot and (comparatively) barren land, and find they need clothes to shield their nakedness from the unforgiving sun.

Pure speculation, I know, (and not without a certain poetic license), but whatever the role clothes have played in allowing humans to populate the globe, it looks like sex is what has made us human.

Enjoy.

This message has been edited by RAZD, 06*11*2005 10:55 PM


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}


This message is a reply to:
 Message 1 by RAZD, posted 04-23-2005 6:13 PM RAZD has responded

Replies to this message:
 Message 72 by RAZD, posted 06-30-2005 9:49 PM RAZD has responded

  
RAZD
Member
Posts: 19089
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5


Message 72 of 131 (221020)
06-30-2005 9:49 PM
Reply to: Message 71 by RAZD
06-11-2005 10:52 PM


Re: last addendum
just ran across this "news" item (more like gossip actually), from
What Makes a Man Look Sexy:

A clean-shaven face is preferred by 42 percent, while 31 percent like it to be a little rough on the chin. Depending on the lady in question, a little chest hair would also be nice. Some 40 percent say a chest hair trim is fine by them, while 28 percent say a man's chest is supposed to be hairy. Another 22 percent would like to see their man hairless. (Ouch!) And while most guys don't do much with their eyebrows, fully 63 percent of women would like to see them groomed. When it comes to back hair, 55 percent of women say hairy men should wax, trim or pluck it if it pokes out of their collar, and 35 percent say any back hair is too much!

Looks like sexual selection is alive and well ... if you can trust anecdotal evidence in a gossip column ...

enjoy


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}


This message is a reply to:
 Message 71 by RAZD, posted 06-11-2005 10:52 PM RAZD has responded

Replies to this message:
 Message 73 by EZscience, posted 07-01-2005 9:39 PM RAZD has responded
 Message 103 by RAZD, posted 10-25-2014 1:52 PM RAZD has acknowledged this reply

  
EZscience
Member (Idle past 2712 days)
Posts: 961
From: A wheatfield in Kansas
Joined: 04-14-2005


Message 73 of 131 (221272)
07-01-2005 9:39 PM
Reply to: Message 72 by RAZD
06-30-2005 9:49 PM


Re: last addendum
Yes, that would confirm my own (limited) experiences with female preference. They don't like back hair or unibrows. But what is the basis for this choice criterium? Arbitrary, or some link to a natural selection advantage? Looking across the range of traits apparently selected by female choice, most are very arbitrary (e.g. tail length, bright coloration) with little adaptive value. On the other hand, a man choosing a women based on hairlessness seems plausibly linked to natural selection. Hairlessness correlates with youth and hence an extended period of residual female fertility. And yet in males, hairiness is a sign of physical maturity that is generally deemed desirable by females, older males being of proven genotypic fitness. Is the female choice component of SS generally indicative of a tendency among females to choose traits that run counter to what is adaptive under natural selection? Could this explain many of our (men's) frustrating experiences trying to impress women with behaviors we would logically assume them to construe as adapative and, therefore desirable, only to be passed over for Joe Hot-rod with his souped-up trans-am and shoe-size IQ?
This message is a reply to:
 Message 72 by RAZD, posted 06-30-2005 9:49 PM RAZD has responded

Replies to this message:
 Message 74 by RAZD, posted 07-02-2005 9:21 AM EZscience has not yet responded

  
RAZD
Member
Posts: 19089
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5


Message 74 of 131 (221304)
07-02-2005 9:21 AM
Reply to: Message 73 by EZscience
07-01-2005 9:39 PM


male\female preference ... ladies?
which curiously ties in with the bluejeans and t-shirt preference noted in the article

perhaps one of the ladies on the site could comment?


we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}


This message is a reply to:
 Message 73 by EZscience, posted 07-01-2005 9:39 PM EZscience has not yet responded

  
RAZD
Member
Posts: 19089
From: the other end of the sidewalk
Joined: 03-14-2004
Member Rating: 2.5


Message 75 of 131 (248712)
10-03-2005 9:15 PM


for david
bump
Replies to this message:
 Message 76 by Graculus, posted 10-03-2005 11:49 PM RAZD has responded

  
Prev1234
5
6789Next
Newer Topic | Older Topic
Jump to:


Copyright 2001-2015 by EvC Forum, All Rights Reserved

™ Version 4.0 Beta
Innovative software from Qwixotic © 2017