Iguacu Falls, which lies at the junction of Brazil and Argentina, rivals Niagara Falls in stunning beauty. Iguacu is longer by far, stretching over several kilometers, with islands between parts of the falls. Except in one place, however, it is not as thunderous. That place is known as The Devil's Throat. By a trick of geography it is possible to stand very close to the waters rushing down the throat. You stand, however, below the crest of the falls, to one side, looking up at its might. And there you see an example of adaptation which takes your breath away. You have to imagine that there are clouds of spray, there are rainbows, there is thunder and there is water cascading down in stunning power. And, from time to time, small birds fly right into the falling waters. The guide, having pointed them out, stands back to answer the obvious question which is 'why are they doing that?" He tells you that they are not committing suicide, they are nesting behind the falls where no predator can get to them. "But they fly right into the falls," you exclaim. "Look closer," comes the reply. So you do, and, with patience, you see that the birds are flying through tiny gaps in the downward flow, gaps made by thin rocks jutting forward. These birds have adapted to their environment. The question is, will we, when our circumstances have changed thanks to global warming?