They haven't changed because their environment has stayed the same. The water they live in bubbles up from deep in the earth, and so it's always the same temperature. But just meters away the environment is very different, away from the thermal vents with the ebb and flow of the water, the temperature fluctuates. Billions of years ago, bacteria were living here too, but as their living conditions changed, they changed as well. From one generation to the next, there were minute alterations. In themselves they were almost insignificant, but these tiny changes started the most amazing process.
--Because if you add up enough tiny changes from generations through millions of generations, you can get a revolutionary transformation.
From being simple bacteria the creatures in these pools became more complicated. Single cells became groups of cells, and groups of cells (became) early plants and animals, and the changes continued. Dozens of species became hundreds, and hundreds turned into tens of thousands. Parts of bodies were adapted to meet new challenges. Great leaps were made. A fish's fins over countless generations developed into legs and it became a reptile. Some reptiles developed feathers and became birds. Others became mammals in every shape and size from blue whale to baboon, every creature we see on the earth today including ourselves. All these happened. It's the miracle of evolution. The human body is just one branch in the huge spreading tree of life that grew from those simple bacteria.
Yet we carry with us the remnants of what has gone before us in our strange past, and there is a place we can go to see just one of those remnants, shaped by one of evolution's truly incredible transformations. It's inside my own head. All we need to do is go and find it.
This is my eardrum, a thin skin stretched tight across my ear canal. But what I want to show you lies on the other side of my eardrum. This device can take me there. I'm inside a huge magnet with a field strong enough to lift a car clean off the ground. It's a magnetic resonant scanner and it can reveal layer by layer what's inside my head. Up to now, this has been the forefront of medical imaging, but we are about to take it one step further.
By putting the medical scans together, we've created a 3-dimensional picture of my own head and I can look at any part of it that I want.
words and expressions
thermal : Of, relating to, using, producing, or caused by heat.
熱的：有關(guān)、用、產(chǎn)生熱的或由熱造成的
ebb and flow :潮的漲落,盛衰,消長
minute:Exceptionally small; tiny微小的, 異常小的，極細(xì)微的
baboon:狒狒
remnant:A surviving trace or vestige:
遺留下來的痕跡或者殘余
eardrum:耳膜
field:magnetic field:磁場
resonant :Producing or exhibiting resonance:
共鳴的，共振的：產(chǎn)生或顯示共鳴的
