But I want to start with the easiest question and the question you really should have all asked yourselves at some point in your life,  不过我今天要从这个最简单的问题开始，这个问题是大家应该在以前问过自己的，

　　because it's a fundamental question if we want to understand brain function.  因为如果大家想了解大脑功能的话。

　　And that is, why do we and other animals have brains?  这个问题是很基本的，那就是，为什么我们和其他动物都有大脑呢？

　　Not all species on our planet have brains, so if we want to know what the brain is for, let's think about why we evolved one.  地球上不是所有物种都有大脑，所以要搞清大脑有什么用，那我们应该先考虑为什么我们进化出了大脑。

　　Now you may reason that we have one to perceive the world or to think, and that's completely wrong.  大家也许觉得我们有大脑是为了感知世界或者思考，其实是完全错误的。

　　If you think about this question for any length of time, it's blindingly obvious why we have a brain.  如果再好好思考一段时间的话，其实我们有大脑的原因很明显。

　　We have a brain for one reason and one reason only, and that's to produce adaptable and complex movements.  大脑的存在，有且仅有一个原因就是为了生成有适应性的、复杂的动作。

　　There is no other reason to have a brain.  没有其他原因了。

　　Think about it. Movement is the only way you have of affecting the world around you.  想想看。动作是你唯一对世界产生影响的方法。

　　That's not quite true. There's one other way, and that's through sweating.  当然也不尽然，另一个办法是通过排汗。

　　But apart from that, everything else goes through contractions of muscles. 不过除了那个以外，所有事情都是由肌肉的收缩来办到的。

　　So think about communication -- speech, gestures, writing, sign language -- they're all mediated through contractions of your muscles.  想想我们的沟通方式--语言、手势、写作、手语--都是由肌肉的收缩来完成的。

　　So it's really important to remember that sensory, memory and cognitive processes are all important,  所以重要的一点就是感知、记忆，认知过程也很关键，

　　but they're only important to either drive or suppress future movements.  但是它们的重要性都只是在于它们能够促使或者抑制动作的发生。

　　There can be no evolutionary advantage to laying down memories of childhood or perceiving the color of a rose if it doesn't affect the way you're going to move later in life. 如果不是能够影响到大家未来生活中的动作的话，能够记住小时候的回忆或者感知到玫瑰花的颜色，在进化这一点上没有任何特别的优势。

　　Now for those who don't believe this argument, we have trees and grass on our planet without the brain,  如果有谁不相信这个说法，我可以举例说不会运动的树和草都没有大脑，

　　but the clinching evidence is this animal here -- the humble sea squirt.  不过有一种动物提供了确凿的证据--不起眼的海鞘。

　　Rudimentary animal, has a nervous system, swims around in the ocean in its juvenile life.  海鞘是一种初等生物，有神经系统，生命初期在海中游动。

　　And at some point of its life, it implants on a rock.  然后在某一时刻海鞘会把自己移植到岩石上再也不移动。

　　And the first thing it does in implanting on that rock, which it never leaves, is to digest its own brain and nervous system for food.  海鞘在岩石上固定后的第一件事就是把自己的大脑和神经系统作为食物消化掉。

　　So once you don't need to move, you don't need the luxury of that brain.  也就是说，一旦不用再移动也就不需要大脑这样的奢侈品了。

　　And this animal is often taken as an analogy to what happens at universities when professors get tenure, but that's a different subject. 并且，这种动物常常被类比到大学里面，教授获得终身职位之后的情况，不过那是另一个话题了。