To understand why our ancestors lost their body hair, we must first consider why other species had fur.
So how did we get so hairless? Scientists have pondered this question for centuries. Finding answers was not easy. The most important transitions in human evolution (such as the emergence of upright gait) were directly recorded in the fossils of our ancestors. But no exact traces of human skin were preserved in any of the remains.
Fortunately, in recent years, researchers have realized that a number of indirect clues about our loss of hair are present in the fossil record. In light of these clues and the understanding gained over the past decade through genomics and physiology, anthropologist Nina G. Jablonski and his colleagues managed to convincingly explain when and why people got rid of their fur.
In addition to explaining one of the oddities of our appearance, according to this scenario, hairless skin itself also played a role in the evolution of other characteristic human features. Including our brain size and our dependence on colloquialism.
Why are there furs ?
To understand why our ancestors lost their body hair, we must first consider why other species had fur. Bristles are a body cover typical of mammals. There is no doubt that one of the defining characteristics of this group of creatures is fur: almost all mammals have at least some hair; most also have dense fur. The hairs provide insulation and protection against stripping, wetting, harmful rays of the sun and parasites or microbes that are potential hazards. It also acts as a camouflage to confuse predators. Thanks to their distinctive patterns, it also makes it easier for members of the same species to recognize each other. Moreover, mammals also use their fur to express aggression or restlessness: for example, when a dog fluffs its neck hair, it gives a clear "stay away" signal to the opposite person.
Although fur serves such important purposes, some mammalian lineages have extremely sparse and dysfunctional hairs. Most of these species are underground or aquatic creatures. In underground mammals, for example, rodents called" naked blind mice", the evolution of hairless has evolved in response to living underground in large colonies. In this way of life, fur becomes an excess, because animals do not see each other in the dark, and sociability consists in gathering together to warm up. In marine mammals that never go ashore, for example whales, hairlessness reduces friction on the skin surface, making it easier to swim and dive long distances. To compensate for the absence of external insulation, there is a layer of oil under the skin of these animals. In semi-aquatic mammals, for example, otters usually have dense and waterproof fur on the contrary. This fur makes it easy to stay on the water, trapping the air into it to provide buoyancy. Of course, it also protects the skin when it's on land.
The largest of the terrestrial mammals - namely elephants, rhinos and hippos-have also developed hairless skins, as they constantly face the risk of overheating. The larger an animal, the less surface area it has compared to its total mass. For this reason, it becomes difficult to save your body from excess heat. Mice and other small mammals, on the other hand, have a high surface-to-volume ratio, so they often struggle to maintain adequate heat. During the Pleistocene Epoch, which covers time from about 2 million years ago to 10,000 years ago, mammoths and other relatives of modern elephants, as well as rhinos, had furs because they lived in a cold environment at the time. External insulation maintained body temperatures while reducing nutrient requirements. But today, all mega herbivores live in very hot conditions, so fur would be deadly to them.
Human nakedness, on the other hand, is not a result of adapting to life underground or in water. The once-popular assumption of" aquatic ape " has also now expired. And it's certainly not a furry thing that comes from being too large. Our furless body seems to be about staying cool, given our superior sweating ability.
Sweat
Staying cool is a big problem for many mammals, not just those with a large build, especially those who live in warm areas and produce excessive amounts of heat over long walking or running distances. These animals must carefully regulate their body temperature, because their tissues and organs, especially their brains, can be damaged by excessive heat.
Mammals have developed several tactics against overheating. For example, dogs breathe quickly, many species of cats are active in the evening, which is usually cooler, or the majority of antelopes breathe through their noses, cooling the blood in their veins through small veins located in their noses. But in primates, including humans, sweating is the primary strategy. Sweating gives the skin coolness as a result of the evaporation of water released through the skin with the heat it receives from the skin when it exits the body. All this body cooling mechanism works according to the same principle (cooling by evaporation), an ingeniously developed method of preventing damage to the brain and other organs due to overheating.
But not all sweats are the same. Mammalian skin contains three types of glands; sebaceous, apocrine and eccrine. These glands work together to produce sweat. In many species, the sebaceous and apocrine glands are the dominant sweat glands and are located close to hair follicles. The secretions of these glands turn the hair into a greasy, sometimes bubbling mixture (think of a racehorse remaining in sweat when it runs). This type of perspiration helps the animal cool down. But the ability of heat to dissipate and disappear is limited. According to a conclusion reached by researchers from the University of Iowa about 20 years ago, the cooling effect decreases as the animal's skin gets wet and covered in this thick oily sweat. The extinction of activity gradually increases because evaporation occurs on the surface of the fur, not on the surface of the skin, which prevents heat transfer. Furry mammals experience hyperthermia (heat exhaustion) and collapse when forced to perform prolonged exercise.
In addition to having no fur, humans own an extraordinary number of eccrine diapers. This number varies between 2 million and 5 million, allowing up to 12 liters of thin, watery sweat to be produced per day. Eccrine glands do not cluster near hair roots, but instead are located relatively close to the surface of the skin and discharge sweat through small pores (holes). This combination of bare skin and watery sweat causes sweat to accumulate directly on the bare skin, rather than directly on the fur, and prevents people from overheating. Thanks to this cooler system, we can give the horses the upper hand in a marathon on a hot day.
Show Some Skin
Humans are the only primate species without fur, and something must have happened to cause naked and sweaty skin to appear since our humanoid lineage, where we split up with our closest relative, the chimpanzees, due to the fact that they have too many eccrine glands. Maybe this transformation began with my first change. By using animal and plant fossils and reviving ancient ecological conditions, scientists determined that the Earth entered a phase of global warming that began about 3 million years ago and had a drying effect in East and Central Africa, where our human ancestors lived. With this decrease in regular rainfall, wooded environments offering open grasslands were preferred by ancient humans, and the food that our ancestors fed on --fruits, leaves, roots and seeds-- began to be rare, and their seasonal accessibility decreased, just as with fresh water sources.
In response to this shrinking of resources, our ancestors were forced to abandon their eating habits, which were relatively hasty. In order to find only water and get enough calories, they constantly entered an active lifestyle, moreover, they had to travel long distances to find water and edible plants. In the archaeological record of about 2.6 million years ago, with the appearance of animal bones and stone tools, it became clear that humans began to add meat to their diet at this time. Animal foods were very rich in calories compared to plant foods, but they were rarer in the land. Therefore, carnivorous animals had to roam wider and more distant lands than herbivores in order to be able to provide sufficient food. Game animals were also moving targets, and the prey needed to be protected, which meant spending more energy on being able to obtain meat from the hunters ' perspective.
As for human hunters and scavengers, natural selection has turned australopithecian humans, who spend part of their time in trees, into long-legged ones capable of running and walking. (This modern form also saved our ancestors from being dinner at times.) But this increased level of activity came at a price: a very high risk of overheating. Beginning in the 1980s, Peter Wheeler of John Moores University in Liverpool, England, published a series of articles in which he portrayed how our warm ancestors emerged from the Savannah. Wheeler's study, along with research that my colleagues and I published in 1994, reveals that as time spent walking and running increased, when muscle activity gained heat internally, hominids increased both eccrine sweating skills and lost body hair.Nov. So they were able to avoid overheating.
And when did this transformation occur? Although the human fossil record does not protect skin, researchers have a rough idea of when our ancestors began their modern forms of movement. With the independent research by Lieberman Johns Hopkins University Christopher Ruff, about 1.6 million years ago, a primitive member of our genus called Homo ergaster, a rate that has a modern body, and has revealed that a long walk and that would allow it to run. Moreover, the details of the joint surfaces of the wrist, knee and hip make it clear that these hominids actually affect themselves in this way. So, according to the fossil record, the transition to bare skin and an ecrine-based perspiration system must have begun to emerge 1.6 million years ago to offset the larger heat loads that accompanied our ancestors ' new grueling lifestyle.
Another clue as to when hominids developed bare skin came from research into the genetics of skin color. In a masterful study published in 2004, Alan R. Of The University of Utah Rogers and colleagues studied human MC1R gene sequences, one of the genes that produces skin pigmentation. The team showed that a certain type of gene, always found in Africans with dark pigmentation, appeared 1.2 million years ago. It is believed that early human ancestors had pink skin covered with very black fur, like a chimpanzee. Therefore, the development of permanent dark skin was likely following the loss of sunscreen body hair. Rogers ' estimate thus provides a minimum date for the hairlessness to come out.
Overcoming Heat
Bare skin is not the only adaptation in the extremely hot climates where our ancestors lived, where humans evolved to maintain normal body temperature. At the same time, it has developed longer limbs and thus increased the surface-to-volume ratio, which makes it easier to get rid of excessive heat. This trend seems to continue today. The best evidence of this ongoing adaptation comes from East African populations such as the Dinka, an ethnic group living in Sudan. It is certainly not a coincidence that these people living in one of the hottest places on earth have extremely long limbs. So, why do modern people develop limb proportions that vary in such a wide range of sizes? As our ancestors migrated from tropical Africa to cooler parts of the world, selection pressures also changed in a way that revealed the evolution of various body types.
Lice and people
In recent years, researchers have focused on lice in an effort to find evidence of why people lose body hair. In 2003, Mark Pagel of the University of Reading and Walter Bodmer of the John Radcliffe Hospital suggested that people shed their hair to get rid of disease-spreading lice on their skin and other parasites that settle on the hair and maintain skin health. Other researchers conducted studies on head and body lice to get an idea of how long after our ancestors started wearing "clothes" after they were naked. Although body lice feed on blood, they can also live on clothes. Thus, the origin of body lice provides a minimal estimate of the appearance of human dress sense. By comparing the gene sequences of organisms, researchers can develop a rough estimate of when the species appeared. Such analysis of lice reveals that head lice have been present in humans since the beginning, but body lice have evolved later. The emergence Times of these species indicate that they were naked more than a million years before humans “dressing up.”
Appearance
‘How did nudity evolve in humanoids? the answer to his ’ question ‘is why and when did your body become naked?'it's less known than the answer to his question. Determining the genetic evidence for the evolution of nudity is quite difficult, as there are many genes that contribute to the appearance and function of our skin. However, from large-scale comparisons of DNA code letters or nucleotides in whole genomes of different organisms, a number of clues can be obtained. Comparing human and chimpanzee genomes reveals that the most important difference between chimpanzee DNA and our DNA is in the codes of proteins that control skin properties. Human versions of some of these genes encode proteins that help make our skin particularly waterproof and scratch-resistant. These are critical properties that should be present on the skin in the absence of protective hair. The suggestion that the arrival of certain gene variables contributes to nudity by mitigating the consequences of nudity is made through these findings.
The superior blocking capacity of our skin is due to the structure and character of the outermost layer of the epidermis, called the stratum corneum (SC). SC can be described as a brick and stucco structure in buildings. In this order, we can compare multiple layers of flat and dead cells called corneocytes, which contain crest protein and other substances, to bricks. Also plaster the ultra-thin layers of lipids that surround each of the corneocytes.
It can be said that the majority of the genes that drive SC Development are ancient. In addition, the sequences of these genes are fairly well preserved in vertebrates. Genes that strengthen human SC have obvious signs, so these genes are important for survival. These genes encode the production of unique combinations of proteins that occur only within the epidermis, including the original types of keratin and involucrin. In many laboratories, the specific mechanisms responsible for regulating the production of these proteins are being worked out.
Other researchers are investigating the evolution of keratins in body hair with the aim of identifying the mechanisms responsible for the rarity and fineness of hair on human skin. In one of the studies on the relevant topic, Roland Moll of Philipps University in Marburg and his colleagues showed that the keratins in body hair are quite sensitive. For this reason, hair on the human body can be plucked or broken more easily than that of other animals. According to this study, published in 2008, human hair keratins were not as important for survival as those of other primates during evolution, and therefore they were weakened.
Geneticists are also trying to answer the question of how human skin contains so many eccrine glands. Due to changes in genes that determine the fate of Epidermal stem cells, this accumulation is almost certain to occur. In the early stages of development, the groups of epidermal stem cells in certain regions of sub-interacts with the cells beneath the skin, the hair follicle stem cells and genetically transmitted into chemical signals in these cells, eccrine glands, apocrine glands, oil glands, or simply directs the differentiation of the epidermis. Many research groups are investigating how epidermal stem cells are identified and preserved. These studies will reveal what drives the fate of embryonic epidermal cells and how these cells turn into eccrine sweat glands in humans.
Not Completely Naked
Although we have become naked apes, evolution has left parts of our bodies covered in hair. So any explanation as to why people have lost their fur should also account for why some areas still remain a little bit. Hair in the armpits and groin probably both release pheromones (chemicals that serve to get a behavioral response from other individuals) and help keep these areas moist during movement.
Hair on the head, on the other hand, acts as a shield for overheating, which will most likely occur in the upper part of the head. This idea may sound illogical, but having dense hair on the head creates a layer of air barrier between the hot surface of the hair and the sweating scalp. So on a hot and sunny day, the hair absorbs heat, while the air barrier layer remains cool and the scalp sweats, allowing the sweat to evaporate towards this air layer. Tight and curly hair provides optimal head protection in this context, because it increases the thickness of the space between the surface of the hair and the scalp, allowing air to enter this space. There are many things that have not been discovered about the evolution of hair in humans, but it is possible that having tight curly hair is the initial state of modern humans, and other hair types evolved as humans spread out of the tropical African region.
And when it comes to our body hair, the question becomes why they vary so much. As well as societies with members whose entire body has very little hair and hair, there are also societies with individuals whose body is covered with feathers and hair. Those whose body is covered with very little hair tend to live in the tropics, while those who have a lot of hair on their body tend to live outside the tropics. However, these body hair in people living in non-tropical areas does not provide significant warmth.
This variability in hairiness is certainly due to the amount of testosterone, because in all societies, men have more body hair compared to women. Some theories that explain this imbalance attribute it to sexual selection. For example, one of these theories suggests that women prefer men with busier beards and thicker body hair, because these traits occur together with power and sexual power. Another claims that men develop a preference for more childlike characteristics in women. These are interesting hypotheses, but no one has yet tested them on the modern human population, so we don't know if hairy men, for example, are really stronger and more fertile compared to more ruddy men. In the absence of experimental evidence, why human body hair varies in its current form is still someone's guess.
Content With Nudity
The loss of hair in the evolutionary process, of course, does not mean that everything will end, but its effects are not underestimated at all. That is, in the phases of human evolution in the process that followed hairless, this process had very strong results. Losing a large part of body hair has made it possible for excess body heat to spread through the eccrine glands by sweating, and thus our organ, which is most sensitive to heat, namely our ‘brain’, to become the effective and large we have today.
Australopithecae had a brain of 400 cm3, close in size to that of modern chimpanzees, while Homo ergaster had a brain almost twice the size of this. In a million-year evolutionary process following Homo ergaster, the human brain gained an extra 400 cm3 volume, reaching its present modern size. Of course, not all the evolutionary processes that lead to the formation of the modern brain consist of this. For example, all genetic and environmental factors that stimulate the formation of gray matter tissue and folds that cover the brain are also of great importance in explaining the functional position of the brain today. However, it can be said that the reduction of body hair also paves the way for a developed brain and facilitates the taking of an evolutionarily important big step.
However, a number of social repercussions of 'hairlessness' have continued. According to our emotional-situational position, the contraction and relaxation of the small muscles located at the bottom of the hair roots or hair follicles involuntarily makes our hair stand up, shudder. At this point, it must be said that we are not very good at showing our feelings with our feathers. Because the hair and hair density that we have lost has made it difficult for us to show our feelings in this way, as our feathers are thin and weak, unlike furry creatures such as cats and dogs. Hairlessness has again led to the fact that we cannot have characters to introduce ourselves through our hair, such as zebras, in short, we cannot communicate through our hair. This has formed the subtext of a group of scientists suggesting that one of the reasons why we develop our facial expressions, use a lot of gestures and facial expressions, and even develop complex language structures, is that we are ‘furless’ creatures.
It is very likely that the cosmetics we use today, body paints, maybe even tanning, even clothes and fashion, if we go further, arose with the need to cover up a similar lack of character. Looking at the whole, we can say that losing our fur is not only what makes us cooler, more developed brains; it's what makes us ‘human’.