Science in Seconds with Timothy Bromage - Part 1

February 27, 2010

Brit Trogen


Dr. Timothy Bromage is a renowned researcher of human evolution, professor of Biomaterials and Biomimetics at NYU, and the 2010 recipient of the Max Planck Research Award, valued at $1.2 million.  In addition to fieldwork leading to the recovery of the oldest known specimen of fossil in the human genus, he recently discovered a previously unrecognized "long-period rhythm" in bone microstructure, providing for the first time a basis for understanding the connection between chronobiology and the life history of an organism. 


[Interview has been edited for length and clarity]


BT: Dr. Bromage, your research uses ancient teeth and facial bones to study the life history of hominids. How exactly can you tell a story using teeth?

TB: The fascinating thing about teeth and their usefulness, first of all, is that because it’s an extremely hard tissue—it’s 97% mineral—it survives in the fossil record extremely well. So whatever you can do with teeth, you can do it not only in modern species but also for fossil species.

Of course, to study early human evolution the only evidence that exists is hard tissue evidence from the teeth. But teeth provide a window into life history. They can reveal something about the pace and the pattern of the life of an animal.

BT: Can you give an example of that?

TB: One example is the eruption of the teeth. For all primates the eruption of the first three molars rough out the thirds of the growth and development periods; the first molar at the point one third in, the second at two thirds, and the third molar at the end of growth and development. A human erupts its first permanent molar around age six. A chimpanzee around age three. A macaque monkey say around one and a half.

So because we have a very much longer growth and development period, everything is longer. Our age at sexual maturity is later. Our age at first breeding is later. Our lifespan is longer. All our life history has been pulled out and enlarged to accommodate a long-lived, large bodied, big brained primate. And this is just [what you learn from] the eruption of the teeth. But it shows you how dental development tells you something very exquisite and personal about the way a species grows up.



BT: You've been credited with discovering a new biological rhythm.  Can you elaborate on how that came about?

TB: Well, this was one of the recent paradigm shifts that was focused on by the Max Planck Society and Alexander Von Humboldt  people. In the field of biological rhythms it’s well known that there are seasonal rhythms and annual rhythms. And circadian rhythms—daily rhythms—are something for which there are whole journals devoted to researching. But that community, if you tell them there are long-term rhythms, they just simply don’t believe you. Because how could an entire science of chronobiology have missed something so fundamental?


Well I’ll tell you why. The reason is, all of the people who do work on biological rhythms use rats and mice and hamsters. Well, long period rhythms are related to body size.  So rats and mice and hamsters don’t have long period rhythms; they only have the circadian rhythms because they’re very small body size. Small bodied primates that are around a kilo or so only have a long period rhythm of two days. And then as you move into larger body size you find three day [rhythms], and four day, five, six, seven, eight, etcetera.

"Dental development tells you something very exquisite and personal about the way a species grows up."

Now, we knew that for humans, when we're kids and our teeth are growing, every 8 to 9 days or so the enamel forming cells actually change the way they produce the enamel for several hours—the cells change the way they produce their matrix. And that becomes visible structurally using a microscope if you later take that tooth and make a section of it with a saw, and look at it under a microscope. You actually see this as a microstructural event. 


And that was a completely enigmatic feature. Nobody really knew what [these events] were. People had suggested before that the long period rhythm was related to body size. But why would a tooth be related to the body size of an animal? It doesn’t make any sense. 


And then one day the epiphany occurred when we discovered that that long-term period actually has nothing to do with teeth—it’s about bone. Or really, it’s about the development of the whole animal, but we see it in bone. And suddenly it all made sense. Long period rhythm is about the amount of bone being laid down. To carry your body mass around you need a certain amount of bone mass. They’re scaled to each other. 



Now, this rhythm is a very much larger package of things, because it’s not only controlling the scaling of the size of your bone to your body, but everything to your body. The size of your liver to your body, the size of your kidney, your muscle mass. All of the tissues and organs need a cell division rate which is compatible to keep up with the developing body as it grows larger.

So this rhythm is probably actually generated in a metabolic pathway that controls the rate of whole body metabolism. Which is very likely generated in a part of the brain called the hypothalamus. And this long period rhythm is a mechanism that mammals probably tugged on through natural selection and evolutionary processes to affect increases in size, and to fill various ecological niches.

So this ended up being something a lot bigger than just understanding how bone and tooth relate to each other. And even bigger than the early human.


For more information about Dr. Bromage and his research, visit his webpage at



Email (optional)


© 2010 Science in Seconds. All rights reserved.     Disclaimer  |  Contact  |  Subscribe
Friend Science in Seconds on Facebook Follow Science in Seconds on Twitter Science in Seconds RSS Feed