试题详情
阅读理解
The brain of a woodpecker (啄木鸟) experiences a seemingly catastrophic impact every time its beak (喙) meets wood. "When you see these birds with hard beaks, flexible tongues and strong neck muscles in action, hitting their head against a tree quite violently, then as humans we start wondering how these birds avoid getting headaches or brain damage," says Van Wassenbergh, a researcher at the University of Antwerp in Belgium.
In the past, scientists have suggested the bird's brain is protected from the impacts, perhaps by a beak that absorbs some of the force, or something in its head that acts as a cushion (缓冲物). But Van Wassenbergh wasn't convinced. So he led a team to settle the issue using high-speed video of woodpeckers in action.The videos revealed some remarkable details. For example, "they close their eyes at the moment they impact the wood," Van Wassenbergh says, to protect their eyes from pieces of wood.
The videos also showed that woodpeckers' beaks often get stuck in the wood. But they break free almost instantly, thanks to a clever beak design that provides independent motion of the upper and lower beak.
What the videos did not show is any sign that the woodpecker's brain is somehow cushioned. "The way we see the head behaving is very rigid, like a tool hitting wood," Van Wassenbergh says. That means the organ repeatedly experiences slowdowns that would cause an injury in a human brain.
Yet the woodpecker brain is unharmed even after thousands of impacts in a single day. That is possible because a woodpecker's brain is protected—not by cushioning, but by its tiny size and weight, Van Wassenbergh says. "An animal that has a smaller size can stand higher slowdowns" he says. "That's a biomechanical law."
That idea was suggested in 2006 by Lorna Gibson, a professor at MIT. Now, it has been confirmed by Van Wassenbergh's high-speed videos.A woodpecker's brain is about 700 times smaller than a human brain. "That is why even the hardest hits we observed are not expected to cause any injury," Van Wassenbergh says.
试题所涉知识点
