INTRODUCTION
Hair forms an integral part of the human body. It is a defining characteristic of mammals.1 There are 193 species of monkeys and apes. One hundred and ninety two of them are covered with hair. The exception is naked ape called Homo sapiens.2 In most of these species functions of hair include retention of heat, sexual dimorphism, attraction of mates, protection of skin and reflection (or absorption) of sunlight. Before understanding various theories of hair evolution let us first take a quick look at milestones in evolution of planet earth and human being.
EVOLUTION OF LIFE ON EARTH AND HUMAN EVOLUTION
Formation of earth and starting point of life on earth is still a great mystery. There are many milestones in this process. Human evolution starts as early as 55 million years ago (MYA) in the form of appearance of primates on earth and goes through various stages to the formation of Homo sapiens 200,000 years ago. This process in addition to other aspects involved transition of hairy primates into less hairy modern human being (Table 1 and Fig. 1).
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Figure 1: Evolution of Homo sapiens3
EVOLUTION OF HAIR
It is commonly believed that hair evolved to help retain body heat, because it is an excellent heat insulator.4 This, however, is a pure speculation. All primates have thick, coarse hair called fur, and explanations as to how this fur was lost in human evolution are deficient and contradictory. One really does not know that to maintain thermoregulation, whether warm bloodedness (endothermy) evolved first or hair evolved first. Our primates were totally covered with fur and now body hair of men and women are purely vestigial structures.5
Proposed Theories of Hair Evolution
- From scales
- From sensory appendages involved in regulation of temperature
- From neural crest cells involved in detection of touch sensation.
Evolution from Scales
Most Darwinists believed that hair evolved from scales. Although, both scales and hair are preserved well in fossil record, no confirmed evidence of hair evolution has been found after more than a century of searching. The scientists have not been able to determine the exact time when hair evolved. Some mammals, such as the Order Pholidota, have both horny scales and fully developed hair. Further proving this theory incorrect is the fact that, no animal has less than fully developed hair; none has structures that are morphologically in-between hair and scales or even hair that is not fully developed.
Evolution from Sensory Appendages involved in Regulation of Temperature
On the basis of anatomical, developmental, neurological and paleontological data it is suggested that hair arose from a highly specialized sensory appendages of mechanoreceptor function which facilitated thermoregulatory behavioral activity.6 The insulatory properties of this “protopelage” subsequently developed into a sensory appendage involved in regulation of temperature.
Evolution from Neural Crest Cells involved in Detection of Touch Sensation
There is theory proposed where it is suggested that body hair develops from migrating neural crest cells which induce patterns of tiny placodes that mature into hair follicles equipped with mechanoreceptors. These include lanceolate endings (velocity detectors excited by hair deflection), Ruffini receptors (tension receptors activated as hair is bent), and Merkel cells (slowly adapting sensors). In 5ontogeny, hair is first sensory, and only later does it insulate, as underfur thickens and thermoregulation matures.7
LOSS OF HAIR IN HUMAN EVOLUTION
Darwinists claim that mammals evolved hair primarily as a result of sexual selection and also for protection and heat insulation.8 Darwin and many others9 were very emphatic about the importance of sexual selection in primate evolution, and tried to explain human nakedness by selection. Cooper10 argues that on one side Darwin taught that “sexual selection” selected for hair in prehumans, and on the other hand “sexual selection” selected for hairlessness. The latest theory is that humans lost their hair to reduce their vulnerability to fur-loving parasites.11 Darwinists also admit they have no idea why humans did not lose all their body hair, including that on the head, pubic, and auxiliary hair.10 Actually, humans have more hair than a chimpanzee; the difference is that most human hair consists of the almost invisible, fine hair (Figs 2A to D).
EVOLUTION OF HAIR IN HUMANS
One needs to answer following questions for better understanding of human hair evolution.
- Were there any structural changes in hair?
- Why did body hair become fine and less dense?
- Why did head hair become long and dense?
- Why did pubic hair stand out prominently?
Were there Any Structural Changes in Hair with evolution?
Hair existed as a fully developed modern hair in fossil record. This means that the ancient hair has been found to be identical to modern hair in all respects. Hair of different mammals is often distinctly different, and no evidence exists that the hair from “more advanced” mammals is more evolved than that of “less advanced” mammals (such as rodents). They are just simply different. Scientists believe that mammalian hair evolved only once and never reversed or modified further. What does this mean? There has been no evolution in hair structure in last 200,000 years.
Why did Body Hair become Fine and Less Dense with Evolution?
Human Nudity Theories
- Movement of humans from forest to city—into shelter and body is covered with clothes. So there is no need for thermoregulatory function of hair.
- To reduce parasite load.
- Sex selection theory: Selection of less hairy men/women as partners.
Why did Head Hair become Long and Dense?
Head hair is much longer than hair elsewhere on body and it continues to grow for long periods. This lengthening has involved several evolutionary changes like faster rate of growth, longer growing phase, increased density and greater resistance to physical damage.12,13 Head hair is a perfect billboard upon which individuals can advertise their social standing. Good grooming is a social enterprise. Head hair grows simply to be cut and coiffed.
A gene called FGF5 studied in animal models inhibits hair growth. Single mutation in FGF5 promoted hair growth. 6Human head hair might also keep growing because it has become insensitive to growth inhibitory factors produced by FGF5 or similar genes.14
There are 10 main genes for the hair keratin, 9 of these are almost identical in humans, chimps and gorillas. The 10th, phi hHaA, is notably different. It is a pseudogene. This mutation occurred some 240,000 years ago. This is a time when humans acquired head hair that continues to grow.15
Why do Pubic Hairs Stand out Prominently?
Humans are the only mammals with prominent pubic hair. Pubic hair indicates prospective sexual partners and mating with that individual could be potentially a fruitful exercise. Pubic hair would have arisen only after we became “naked apes”, causing it to stand out so vividly against the backdrop of an otherwise hairless body says Robin Weiss, a virologist from University College, London in an article published in Journal of Biology.16 Pubic hair during evolution has become bushy and prominent and acquired a new role as a prominent sexual ornament, a visual signal of sexual maturity and possibly a reservoir for sexual pheromones.
WHAT’S NEXT?
There are two possibilities; either we will retain hair or we will not. As far as pubic hair is concerned, it is an ornament, worn or shed off depending on mood of the day. Possibility is that it may continue to evolve with evolving sex life.
As far as body hair is concerned, everyone likes it clean. Excess body hair is being disliked and many seek treatments to get rid of it. Possibility is that future generations will have less of body hair.
Scalp hair is the most sought after thing and is influenced by many genetic and environmental factors. A lot of research is currently being directed at stem cell research and other areas which can help retain the god gifted crown on human being. Time will only tell what future holds for us, but for today, the scalp hair loss is causing a great concern in masses and will continue to do so in years to come.
CONCLUSION
- Hair structure is not undergoing evolution, but hair distribution is.
- Body hair will diminish in the coming years with human evolution.
- Pubic hair is ornamental and may or may not be affected by evolution.
- Scalp hair has been affected tremendously by recent environmental and genetic changes and alopecia is developing in a larger population at an earlier age. Only time ahead and future genetic research will answer fate of human scalp hair in future evolution.
REFERENCES
- Denton M. Evolution: a theory in crisis. New York: Adler & Adler; 1986.
- Morris D. The naked ape. New York; McGraw-Hill; 1967.
- Unmasking Evolution. [online] Available from www.unmaskingevolution.com. [Accessed February, 2016].]
- Wong K, Simmons N. What is the difference between hair and fur? Sci Am; 2001.
- Wells HG, Huxley JS, Wells GP. The science of life. New York: Doubleday; 1931.
- Maderson PFA. When? Why? and How?: Some speculations on the evolution of the Vertebrate Integument. Am Zoologist. 1972;12:150–71.
- Rowe TB, Macrini TE, Luo ZX. Fossil evidence on origin of the mammalian brain. Science. 2011;332(6032):955–7.
- Darwin C. The decent of man, and selection in relation to sex. London: John Murray; 1871.
- Schwartz GG, Rosenblum LA. Allometry of primate hair density and the evolution of human hairlessness. Am J Phys Anthropol. 1981;55(1):9–12.
- Cooper W. Hair. New York: Stein and Day; 1971.
- Bhattacharya S. Early humans lost hair to beat bugs. London: New Scientist. 2003.
- Khumalo NP. African hair morphology: macrostructure to ultrastructure. Int J Dermatol. 2005;44:10–2.
- Loussouarn G, El Rawadi C, Genain G. Diversity of Hair Growth Profiles. Int J Dermatol. 2005;44:6–9.
- Higgins CA. FGF5 is a crucial regulator of hair length in humans. Proc Natl Acad Sci USA. 2014;111(29):10648–53.
- Winter H. Human type I hair keratin pseudogene phihHaA has functional orthologs in the chimpanzee and gorilla: evidence for recent inactivation of the human gene after the Pan-Homo divergence. Hum Genet. 2001;108(1):37–42.
- Weiss RA. Apes, lice and prehistory. J Biol. 2009;8(2):20.