On my way into my other job, I usually see a sidewalk board from the salon behind us to entice potential walk-in clients. For the past few weeks, the sign has simply said "Your hair shouldn't say 'I give up!'" Uh, okay? A little presumptive, but also reflective of modern culture--to say hair is important is an understatement. Is it smooth, frizzy, curly? What color is it: brown, blonde, blue? Is it the right hair style for the occasion? Is it doing what I want it to do? Why is this one hair not going in the direction it needs to go in?
Brushing societal standards aside, hair is a major point in the timeline of animal evolution and a characteristic of the mammalian class. If you ever get me going on anthropology, I'll somehow end up talking about how we are primates (although talking about this in a blog for a primatology lab is a little redundant). So as primates who have created products, sprays, and pomades to make our hair do whatever we want it to (as well as waxes, lotions, and cream to remove said hair), you would think that we have it all figured out when we study hair in our closest relatives.
Surprisingly, there is little research on hair function and evolution in primates (or more broadly, any mammal). We've taken steps to force hair to do things and look a certain way, and have studied the growth and structure of human hair, but not much else.
Primates have an incredible diversity in their coats between and even within species. By studying primate hair and the context of its morphology and coloration, we can begin to understand our own relative hairlessness.
But how do you go about researching hair?
It's no small feat. The lab is working on this project in collaboration with Dr. Brenda Bradley at the Primate Genomics Lab at George Washington University. Evolutionary forces have an effect on pelage (read: hair/coat) variation, specifically coloration, density, and length. So what evolutionary factors affect hair, you ask?
Hair is critical for many species in maintaining homeostasis. Hair density is a major factor in thermoregulation. On the other hand, coloration can be extremely useful in varying climates. Trade offs can be made between hair thickness (note, not density) and coloration
to assist against heat stress during the day and protect against heat loss at night.
I've indirectly talked about sexual dimorphism and sexual selection in other posts, but exploring these factors in regards to pelage can help us learn more about our own species. Sexual selection can positively or negatively select for certain phenotypic features as a way to determine potential reproductive success. Some studies have related nutrition and growth to hair pigmentation, serving as an indication of the individual's foraging success.
Some primates represent extremes of sexual dimorphism in pelage coloration, for example, the stark contrast between male and female coats in black-crested gibbons (Nomascus concolor). Sexual dichromatism is rare in mammals, although there are more subtle variations throughout the primate order.
Differences in hair thickness between males and females within primates could be a result of body size dimorphism (females are typically smaller than males), although minimal research has been done on this topic.
Another aspect of this discussion and our research is how hair plays into social communication and identification. Like humans, primates have complex social structures and hierarchies, varying from species to species. For primates that live sympatrically with other closely related species, scientists suggest a trend of more complex facial markings. Take, for example, the Titi monkey, and all of the different species distinguished by colorings shown below.
On the other end... Mandrills have colorful faces and colorful butts, with their butts being oddly reminiscent of their faces. Don't believe me? Just hop on Google for a quick search and see for yourself. This matching coloration may function as a way for neonates (read: babies) to imprint on and recognize mom as they are born. Oh, bright colors are the very first thing you see in your life? And mom's face is just as colorful? That's pretty rad.
Primates are incredibly reliant on visual cues as opposed to other mammals, putting an emphasis on species specific coats and markings. Communication could potentially be a main function of hair pigmentation and diversity, but, again, there has been limited research.
So what else can affect hair? We've talked about keeping cool (or warm), sexual selection, and communication and identification. And while this next factor isn't that much of an issue in humans, it could be part of the reason why we are virtually hairless compared to our relatives: parasites. By lowering hair density, thickness, and length, parasites would be more easily detected, and thus removable. It would also make parasitic wounds more visible, and thus easier to clean.
That was a lot.
Thermoregulation, sexual selection, communication and identification, and parasites. These are potential evolutionary factors affecting hair density, thickness, and pigmentation.
I've mentioned before that we don't actually have live primates in the lab, so how are we going about this research?
We've been able to collect photographs of over 900 museum pelts in excellent condition, representing over 150 primate species. Our photographs come from several museum collections, including The National Museum of Natural History, The Harvard Museum of Comparative Zoology, The Yale Peabody Museum of Natural History, the American Museum of Natural History, and the Field Museum of Natural History. We use Photoshop to identify colors on the skins, and Excel to organize all of our numerical data and measurements.
Really, though, this project is a foundation for future research and study of primate hair. It is among the first to provide a comprehensive and quantitative analysis of hair variation for a mammalian group. Through our collaboration with the Primate Genomics Lab, we will analyze and identify genetic differences behind variations in pigmentation and length for primates such as the Eulemur genus. This genetic aspect will cover different regions, sexes, and species.
Only by understanding hair's function in other primates, can we begin to understand why we lost so much of our own.
Female black-crested gibbon with one-year old infant
© Dr. Fan Peng-Fei
Dr. Fan Peng-Fei
Adult and subadult male black-crested gibbons
© Dr. Fan Peng-Fei
Dr. Fan Peng-Fei