Read Online Undeniable by Bill Nye - Free Book Online Page A

animals that eat acacia tree leaves can reach the leaves on the lower branches. But only the giraffes who happen to have the slightly longer necks can keep going and reach and eat the higher leaves that other animals and other shorter members of their tower can’t reach. So when the scarce leaf supply is gone from the lower branches, the tall members of a tower get more food and are more likely to have healthy babies.
    Now, imagine a drought like that happening almost every year for, say, ten years. Like North America, Africa is subject to climate patterns associated with El Niño events in the western Pacific Ocean. Such patterns can last for years. Over the course of a few seasons, a tower (a population) of giraffes might find little to eat. In that case, only the tall would survive. The pressure would be high. Instead of giraffes that were a little bit taller doing a little bit better, the taller ones would be the only ones to make it through the drought. The shorter members of the group would, in just a few years, die out. Their genes would be eliminated quickly.
    This idea illustrates, in simplified fashion, how changes in the environment can select for well-suited genes surprisingly quickly. You can’t stretch your own neck to give your kids long necks. You have to have long-neck genes (or longer-neck genes), and they have to make it into your offspring. Poor Lamarck, smart as he was, did not see how the process really worked. But as modern observers, we have to give credit to Lamarck for even taking on the problem, for even thinking about it.
    While we’re talking about giraffes, there is another remarkable and vital point to be made about evolution and the survival of the “good-enough.” It is an unfortunate linguistic happenstance that “survival of the fittest” sounds so good, because random natural variation does not produce perfectly fit individuals, nor does it need to. Evolution is driven by the idea of “fits in the best,” or “fits in well enough.”
    When we look at the anatomy of a giraffe, we come across a great many surprising and interesting features. First of all, although a giraffe has what seems to us a pretty long neck, a giraffe has seven vertebrae, just as you and I do. Her or his neck is, in a fundamental sense, the same as ours. This is evidence of a common ancestry. Somewhere back in time, there were vertebrate mammals (those with backbones) that gave rise to both giraffes and to us. Seven vertebrae are not very many for the giraffe’s long neck. Having such few, large bones limits the animal’s flexibility. But evolution constrains us all to work with what we’ve got.
    Along this line, the nerve that extends from your brain to your voice box, your larynx, runs down from your brain and past the larynx. It goes right by your larynx like the pavement of a big city beltway. This same nerve runs around an artery near your heart, and then back up to your neck, where it connects to your larynx. It really does. The same is true for a fish, where the nerve from the brain to the gills takes a pretty short route. But with generation after generation, certain animal necks got longer. Gills changed so that they could take in oxygen from the atmosphere rather than take in oxygen dissolved in water. This same nerve kept running the same route. Down from the brain, around a heart artery, then back up to the larynx. That’s another consequence of evolution: Every generation can only be a direct modification of what came before.
    In a giraffe, it’s wild. The nerve runs from the brain down to the animal’s heart, which is in its chest, just like yours, then back up to its voice box, the larynx. If you were to sit down and design a connection from the brain to the larynx, you’d make it just 5 centimeters or so (2 inches). But because animals like us and giraffes came from ancestors with the same kind of nerve wiring, we end up and giraffes