Woodpeckers peck about 12,000 times a day. They bang their heads into trees an amazing 20 times per second, which raises the question: Why don't they get concussions?
Looking at how animals mitigate head trauma was a question that my co-author, Allen St. John, and I asked while writing our new book, Newton's Football. American football is in the midst of a concussion epidemic, and many people are looking for solutions. We figured that one possible place to look for solutions is Mother Nature.
First, we spoke to Prof. Lorna Gibson, a materials science professor at MIT who has studied woodpeckers, and she told us the following: Woodpeckers drum their heads into a hardwood tree at speeds of up to 15 miles per hour. How do they survive these impacts intact? Because of the size of their brains and the physiology of their skulls. A human brain has a mass of 1,400 grams. A woodpecker's brain is only 2 grams. That's the mass of two paperclips.
"It is a scaling phenomenon," Dr. Gibson explained to us. While this might seem like a highfalutin concept, this is something that we instinctually understand. If you dropped your cellphone from your nightstand, it would survive. But if you dropped your laptop from the same height, you might have to take a trip to the Apple store. The same goes for brains: The smaller the brain, the better its chance of surviving an impact. In fact, woodpeckers laugh off impacts that would kill a human. Size matters, and sometimes smaller is better, as you can see in this video.
Secondly, their brains are oriented differently: They're turned 90 degrees in comparison to human brains, which means the force is distributed over a greater area. More area means less force is directly applied to the brain tissue. This wider distribution of force is the trick behind a bed of nails. The multiple points of many nails spread the force of your body weight, while we know that a solitary nail can pierce even the toughest tire.
Finally, woodpeckers survive the 12,000 pecks a day because their brains fit snugly inside their skulls. The lack of space restricts the brain's movement. A concussion results from the collision of the brain with the inside of the skull. If there is no place for the brain to move, there is less chance for a concussion.
I admit that my collaborator and I were a little disappointed to find that woodpeckers don't offer much that's instructive about reducing concussions in humans. So we did a bit more digging and explored an animal that has more to offer by way of solutions: the ram.
Rams are big animals with relatively big brains, yet they engage in a spectacular head-butting ritual. Two animals will collide at speeds of 20 to 40 miles per hour with incredible force, yet they seem to sustain little damage. How?
One obvious trait of rams is their horns.
Now, am I saying that we should add horns to helmets? Sort of.
To understand the ram's horns, I stumbled onto a little-known journal article written by Dr. Andrew Farke. Farke is a paleontologist at the Alf Museum in California who studies horned dinosaurs. Since those creatures are long dead, he researches head-butting rams to better understand the ancient beasts. We spoke to him, and he shed some light on how rams escape this kind of head butting unscathed. A ram's horn is a porous bone that is covered in keratin, which is a protein found in our hair and nails. Keratin is elastic, and this property of the material allows the horns to give a bit under impact. This helps distribute the force, once again by providing greater contact area. But also, the bending of the horns increases the duration of the impact, which reduces the force.
Physicists use a concept called "impulse" to describe a collision. The impulse is equal to the force of the impact multiplied by the time of impact. The amount of impulse in any given collision is fixed, so if you want to minimize the force, you must increase the amount of time. As one increases, the other decreases, and vice versa.
Think of it this way: I toss my toddler nephew into the air. When I catch him with my hands, I allow my hands to continue moving downward. I move with him. If I didn't, he would land in my hands with a jolt, and there would be much crying afterwards. When my hands move with him, I am cushioning his fall by increasing the duration of impact. I am doing what the ram's horns are doing, which is cushioning the blow by allowing more time for the blow to happen. This is also how the crumple zones in cars work, absorbing huge amounts of energy by increasing the duration of the impact.
So if woodpeckers don't provide any insight on football helmets, what do rams have to tell us? That we need new materials in helmets, materials that lessen the force transferred to the brain. Football helmets use the same kind of polycarbonate plastic used in helmets from nearly half a century ago, equipment that was designed to eliminate skull fractures -- which it did -- with little or no regard to concussions. We need new research thrusts that look at how materials absorb force. Such research thrusts may not be as sexy as the Higgs Boson, but they could have direct impact (forgive the pun) on an important issue. We all love thrills, as evidenced by the joy that my nephew exhibits when I toss him in the air. But it's my responsibility to make sure that he doesn't get hurt when we play. All of us who enjoy football are similarly obligated to find ways to keep the sport as safe as it is thrilling.
Learn more about the science behind football in the new title from Random House called Newton's Football.