The history of hair: tracing its roots to early origins
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The history of hair: tracing its roots to early origins
Hair is unique to mammals and has driven mammalian evolution. However, the origins of hair-producing cells, and the genes that code for them, go much further back. Similar genes can be found in a wide range of animals. Dr Wilfred D. Stein was drawn into the evolutionary history of hair after studying treatments for hair health issues. His research involved diving into genome databases to discover the origins of hair-producing cells, and to investigate how similar genes present themselves in other animals.
Talk like a … biophysicist
Amino acids — the molecular building blocks that, when combined, make up proteins
Bioinformatics — a field of science using large databases and statistics to organise and analyse large quantities of biological information
Ectoderm — the cells in an embryo that develop into skin, hair and the nervous system
Ectodysplasin pathway — a cell signalling pathway that controls the development of ectodermal organs such as teeth, hair, and sweat and mammary glands
Epithelium — the cells that line the outer layer of a body’s surface, including the skin
Genome — the complete set of DNA of an organism
Keratin — a fibrous protein that is the main component of hair, feathers and nails
Keratin-associated proteins (KRTAPs) — proteins that interact with keratin in hair and fur and can influence the structure and traits of hair
Mammal — a warm-bloodied animal distinguished by having hair and secreting milk to feed its young
Placode — a thickening of embryonic ectoderm that goes on to form a definitive structure
Trichocytes — specialised epithelial cells that produce hair or nails
Though we are accustomed to it, hair is a curious trait and one only found in mammals. While it can have a range of functions, hair most often helps with regulating body temperature, in particular, insulating against cold conditions to help retain heat. “Hair, wool and fur appeared in mammals around 180 million years ago,” says Dr Wilfred D. Stein from The Hebrew University of Jerusalem. “Hair enabled the earliest mammals to fill an ecological niche as warm-blooded animals, which allowed them to forage during the night.” Human evolution has since changed the role of hair; we have lost most of the insulative hair of our ancestors and what remains is largely used for decoration.
To fully understand how hair evolved, it is necessary to investigate the cellular and genetic mechanisms that enable hair to develop. “Hair is produced by cells called trichocytes,” explains Wilfred. “These cells produce keratin, a structural, fibrous protein, and keratin-associated proteins (KRTAPs).” The KRTAPs provide strength and length to hair and fur fibres, with some helping to provide thicker wool or curlier hair. Not long ago, it was thought that KRTAPs were unique to mammals. Through careful analysis of genome databases, Wilfred and his collaborators revealed that this is not the case, shedding new light on the evolution of hair and potentially adding to our understanding of hair health.
Research beginnings
Wilfred’s path to studying the evolution of hair began with investigating hair health issues, such as baldness. “Alongside collaborators from the pharmaceutical industry, we were working on treatments for skin diseases that affect hair,” he says. “This naturally led to questions about keratins and KRTAPs, which drew us towards investigating how hair evolved.”
Charles Darwin, the father of the theory of evolution, was among the first to think about the evolutionary history of hair after hearing about a family in India who suffered from a hereditary skin condition. Many males in the family had little hair, early baldness, few teeth and dry skin – but this condition was not seen in any women, nor was it ever passed on from father to son. Later, other researchers would conclude that this disease arose from a genetic mutation on the X chromosome.
Intense research in the decades since has uncovered exactly what the family suffered from and which genes are affected. “The condition, ectodermal dysplasia, affects the genes of the ectodysplasin pathway,” explains Wilfred. “This pathway regulates the formation of ectodermal skin appendage organs, including teeth, sweat glands and hair.” During embryonic development, all these organs develop from structures called placodes, which are thickenings of the embryonic epithelium. “Placodes and the ectodysplasin pathway are not unique to mammals,” says Wilfred. “They also regulate the formation of teeth in fish, scales in reptiles, and feathers in birds.”
This indicates that placodes have an important role in hair development, but that something else is required to make hair different from these other appendages. “In evolution, the first placodes appear with non-jawed fish, which produced ‘proto-teeth’ made of keratin,” explains Wilfred. “When jawed fish emerged, they evolved ‘true’ teeth made from bone – also originating from placodes.” Yet, a missing piece of the puzzle remained: when and how did hair evolve its unique properties?
KRTAPs research
Wilfred and his collaborators wanted to understand how the evolution of placodes was related to the evolution of hair-producing cells (trichocytes) and the KRTAPs that they create. “Our research focused on bioinformatics, which involves looking at big genetic databases of many animals to see which have the same – or similar – genes for hair that mammals do,” says Wilfred. “First, we needed to identify and group the genes for KRTAPs, which involved comparing the amino acid sequences of KRTAPs in humans.”
Reference
https://doi.org/10.33424/FUTURUM556
Placodes and the ectodysplasin pathway are not unique to mammals. They also regulate the formation of teeth in fish, scales in reptiles, and feathers in birds.
Diagram of the time course of development of ectodermal placodes showing how, under appropriate timing and location signals, such a placode can produce a tooth or a hair fibre or sweat droplets.
Once these proteins were grouped according to their underlying genetic codes, the team got to work searching genome databases for occurrences of similar genes in other animals. “We showed that proteins closely related to the KRTAPs can be found in animals that took a different evolutionary path to the one leading to mammals many millions of years ago,” says Wilfred. “For instance, sea anemones express two KRTAPs, while zebrafish express one in their heads and one in their ovaries.” In these animals, these proteins have nothing to do with hair – in fact, they do not even interact with keratin. This suggests that the keratin-KRTAP association may be a purely mammalian trait.
Research conclusions
With these findings in hand, the team hypothesised that the combination of placodes and KRTAP-like proteins may have resulted in the origin of hair. “With the system for making placodes already available to them, we theorised that the earliest mammals co-opted some of the already-present KRTAPs, modifying and combining them with keratins to produce a new invention: the trichocyte,” says Wilfred. “The first hairs to evolve were whiskers, used to sense the surrounding environment.” Whiskers evolved in therapsids, mammal-like reptiles that are the ancestors of all modern mammals. Once the evolution of the trichocyte enabled the development of these first true hairs, it opened up new opportunities for the ensuing diversification of KRTAPs. “The platypus, which diverged from the rest of the evolving mammals early on, has around 20 KRTAPs,” says Wilfred. “Humans, on the other hand, have 93.”
These findings are interesting from the perspective of learning more about our own evolutionary origins and those of other animals, but they may also have applications to improve lives. “By understanding more about the factors that had to come together for hair to evolve, we can learn more about the mechanisms that drive hair growth,” says Wilfred. “This can help us understand, and potentially treat, hair health issues, such as premature hair loss.”
Dr Wilfred D. Stein
Emeritus Professor of Biophysics, Silberman Institute of Life Sciences, The Hebrew University of Jerusalem, Israel
Fields of research: Biophysics, biochemistry
Research project: Investigating the evolutionary origin of hair-producing cells
About biophysics
Biophysics involves applying methods and approaches typically used in physics to biological systems, to deepen understanding into how these systems work. It is a diverse field, offering flexibility to specialise in many different areas or use established principles to explore new areas, just as Wilfred did with his research into hair evolution. It can involve the study of biological systems at any level, from the molecular scale, through to cells and tissues, through to how whole organisms operate and interact.
Wilfred’s long career journey has involved the study of a diverse range of research areas. These include:
- Studying the physiology behind the transport of molecules across cell membranes.
- How different concentrations of certain chemotherapy treatments lead to very different effects on the cell cycle.
- The mechanics behind resistance of malaria mutations to antimalarial drugs.
- Mathematically modelling tumour growth.
- Studying the origin of specific genes by examining similar genes across different species.
Biophysics continues to evolve as new scientific frontiers are crossed. “Currently, there’s a lot of work to be done to understand exactly how the brain works,” says Wilfred. “This is the latest research front that biophysicists are now addressing.” Biophysics of the brain, or neurophysics, involves studying the physical properties of the brain, including how electrical signals are generated and transferred, how cells and structures move in space and time, and the movement of fluids around the brain. Studying these processes can lend insights into the physics behind how we process information. Technological advances are opening new doors for this field, giving us an ever-deeper understanding of the brain.
Pathway from school to biophysics
Wilfred recommends building a strong foundation in mathematics, computing, physics and biology at school and college.
At university, a range of undergraduate courses can lead to a career in biophysics, including physics, chemistry, biology and mathematics. Useful modules within these courses include biochemistry, neurobiology, pharmacology, computational biology and bioengineering.
Explore careers in biophysics
The Biophysical Society website is a key resource for learning more about biophysics and interacting with networks of biophysicists. This webpage provides more information about the field, and this webpage explains the career paths available for becoming a biophysicist.
The Hebrew University of Jerusalem, where Wilfred is Emeritus Professor, has a variety of science outreach programmes for schools, including laboratory activities, science festivals and fairs, and science conventions. Find out more.
Biophysicist salaries can vary widely given the diversity of the field. According to Salary Expert, the average salary for a biologist in Israel is around ₪191,000 per year.
Meet Wilfred
I was a ‘guinea pig’ for the first iteration of a biochemistry course during my master’s degree. It was taught by Sydney Brenner, who would later go on to receive the Nobel Prize. This course really piqued my interest in biochemistry and biophysics.
I’ve studied and taught around the world. I began in South Africa, moved to the UK for my PhD in London followed by a postdoc in Cambridge, then took another postdoc in Ann Arbor in the US. I’ve taught at Manchester University in the UK and then at the Hebrew University and Weizmann Institute in Israel. Guest professorships and sabbaticals have taken me to Denmark and the US. In all these places, I found colleagues to interact and work with, leading to valuable collaborations.
I also write memoirs about my family. My late sister-in-law researched the history of her family, and I edited and published her work after her death. This encouraged me to look into my own family history, which ties in closely with my passions around genomics and genealogy.
One of my biggest career moments involved a breakthrough around cell membranes. I was the first person to publish a model of the cell membrane as a lipid layer into which proteins are embedded. These two components make up cell membranes. My work was largely overlooked at the time, but I still remember my excitement as I conceived of this model, an excitement that was an epiphany.
I’m technically retired now, hence my ‘Emeritus Professor’ title. However, I continue to research and publish papers on early animal evolution as I enjoy it greatly. I am also enjoying spending lots of time with my family. My wife and I recently celebrated our 70th wedding anniversary!
Wilfred’s top tips
1. Do research because you find it fun and exciting – don’t just focus on advancing your career.
2. Find good colleagues to collaborate with. Those colleagues will help you unlock talents and abilities that you didn’t know you had.
Do you have a question for Wilfred?
Write it in the comments box below and Wilfred will get back to you. (Remember, researchers are very busy people, so you may have to wait a few days.)
Learn about the development and evolution of the inner ear:
www.futurumcareers.com/how-does-the-inner-ear-develop-into-a-sensitive-hearing-and-balance-organ
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