Undeniable (7 page)

Living things were generally believed to have a soul or a metaphysical quality that was passed from parent to child and even from tree to acorn. In the minds of nineteenth-century naturalists, permanence had been there from the beginning; change was not built in. Yet they suspected that a mechanism for change did exist. How could nature or a deity cause so many forms to arise or be created? Did a creator imbue every seed with a soul? Expressing it in the words of the nineteenth century: How could what they called “homogeneity” become “heterogeneity”? Darwin's descent by natural selection was a result of not only a great step in thought, but also the sidestepping of a great many ideas that missed the mark.

A number of Darwin's predecessors latched onto some aspects of natural selection without getting the fundamentals right. And nobody did a more spectacular job mixing correct and incorrect than Jean-Baptiste de Monet, who went by his courtly, inherited French noble name of Chevalier de Lamarck and is commonly called simply “Lamarck.”

In mid-eighteenth-century France, Lamarck speculated that when animals and plants exercise certain organs, those that use other organs regularly and vigorously would not only enhance the function of said organs, but would pass on the tendency to have an improved or strengthened organ to their offspring. Apparently, he observed that blacksmiths had muscular arms and shoulders, as one might expect from a lifetime of hammering on anvils. He expected that a blacksmith's kids would inherit those arms, passing along big shoulders, or perhaps the ability to develop big shoulders. From there, he drew a bigger conclusion about the bigger system in nature.

It's not hard to see why Lamarck thought that way. We are all familiar with people who follow in their mother's or father's footsteps. If you are the son of a blacksmith, you would grow up knowing more about metalworking than the average person. When you come of age and seek a trade, it's reasonable that you'd have a leg (or a hammer) up on other would-be blacksmiths. It must have reinforced the conclusion in Lamarck's mind. Today, there are a great many major league baseball players who are the sons of major league players. It probably has something to do with being exposed to baseball culture and the details of the rules in addition to inheriting the right physique for the game; but you can see how these factors working together might result in a son following in his father's footsteps. You might think that the more you did something—the more you swung a bat or a hammer—the better you would get at it. Along with that you might conclude that the children of a horseshoer, a barrel maker, a bat swinger, or a ball thrower would tend to inherit these abilities. If that is true of people, why not animals as well?

Seeking to link cause and effect, Lamarck speculated that this supposed ability to change or modify the traits passed on to offspring was the result of a
complexifying force
. If an animal wanted to eat certain leaves, for example, it might develop the right kind of teeth for it, and then pass that beneficial new trait to its offspring. This came to be called the inheritance of acquired traits. It would be a tendency or agent in nature that helps the successive generations build on beneficial modifications that resulted from a previous generation's effort.

Lamarck's speculation was a helpful means to gain insight into the ways in which species change. He was grasping to understand the means by which an organism could gain complexity or specificity and efficacy as he, she, or it reproduces. For me, the iconic example is the giraffe (
Giraffa camelopardalis
). Imagine being a central European thinker and coming upon a giraffe for the first time; because of their unassuming ways and their seeming amicable outlook on life, giraffes are just fascinating. Inevitably you would wonder: How did they get those long necks? Why don't they have regular necks like dogs, cats, and cows? After all, we do not observe giraffes actively stretching their own necks as they grow up. They are just born that way. If you cut the tail of a mouse, its offspring still have tails. If a big-shouldered family stops working as blacksmiths, they still have big shoulders. Lamarck's ideas did not stand up to scientific scrutiny.

We know now that a giraffe's neck, like all its physical attributes, is controlled by genes, and living things in nature cannot alter their genes. All organisms—sea anemones, fireflies, giant squid, miniature poodles, and humans—have to play the genetic hand they're dealt. What Darwin realized, and what Lamarck missed, is that the complexity emerges slowly through a whole population, not quickly within a single person or animal. With that said, researchers have recently discovered an intriguing twist to the story. Under the right conditions, and up to a point, inheritance
can
work the way Lamarck believed it did. Although genes themselves do not change on their own, the way that those genes are activated can change within a single individual's lifetime. This phenomenon is called epigenetic change—changes coming from the outside.

In the not-so-distant future, there may be another way that your genes can change. Scientists are working on gene therapy—ways to alter your DNA to eliminate or obviate a disease, to make adjustments, or to incorporate what we hope are improvements to our genes. Someday it may be possible to make modifications in the so-called germ line, which would result in that new DNA being passed on to your kids. Creepy or fabulous? Crazy or ethical? The possibility of genetic modification reminds me of the need for a scientifically literate electorate. Please stay tuned and vote!

Keeping all of this in mind, let us once again consider the giraffe in its natural habitat. Having traveled in Africa a couple of times and observed giraffes in nature, I can tell you that you don't have to be the world's foremost authority to see that giraffes eat leaves on branches pretty high off the ground. They use their necks to get to vegetable matter that other animals would have to work quite a bit harder to get to. If you were a cat, you could climb out on those branches and gnaw away. But it would be a lot more work. Oh, and cats generally eat other animals rather than delicious acacia tree leaves. Giraffes have another fascinating feature that I didn't notice, until it was pointed out to me. They have very tough tongues and lips. They can just grab onto the thick part of an acacia tree limb and slide their mouths right down the limb to the thin end, stripping all the leaves off as they go. Here's the thing: African acacia trees are loaded with thorns. You and I cannot grab an acacia branch with our bare hands, let alone our bare tongues. Yee-ouch! But giraffes can.

Thinking as Lamarck had thought, you might conclude or presume that the giraffes that we see today got their long necks by just reaching. You might think that just by stretching their necks to get food, giraffe necks would naturally get longer—and so would the necks of their offspring. But no. Darwin reached the correct answer: The ancestors of our modern giraffes, who happened to have slightly longer necks than their contemporaries, were able to reach just a little bit higher on acacia trees than the other members of their giraffe herd, or no kidding, other members of their tower. (It's like school, as in a school of fish. Only this is a tower of giraffes.) The giraffes with longer necks were better—just a little bit better—at getting enough nutrition. So, they were just a little bit better at having babies, too.

The evolutionary pressure to have longer necks was probably stronger when food supplies were scarce. Imagine a drought on the savannah, the African landscape that a European or American might describe as somewhere between a forest and prairie. During the drought the trees that survive probably have fewer, smaller leaves that don't carry as much water as they do when there's been plenty of rain. In this situation, all of the 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 end up with this arrangement, which seems quite odd at first. After you mull it over, it's just what you'd expect from fish, from yourself, and from giraffes.

The same must be true of a giraffe's tongue and lips. Each generation of proto-giraffe, the ancestors of modern giraffes, had successively tougher tongues. A tough tongue enabled you, as a proto-giraffe, to get a little more to eat from the leaves of high branches. Eventually, a generation of giraffes was born that could eat high and thorny acacia leaves.

To drive this idea home, join me in a little thought exercise. Imagine a bicycle. Now, imagine a two-wheeled hand truck or a two-wheeled cart, the kind you see city dwellers bring to the grocery store. Now, imagine making changes to the cart or hand truck so that it becomes a bicycle—but making those changes step-by-step, in accordance with evolutionary principles. You would have to stretch the cart into a parallelogram shape or something similar, so that the wheels were one before the other rather than side-by-side. The wheels would have to be bigger. The tires would have to hollow out and become filled with air. You might have to modify the axle to become a chain. Maybe the handle that goes over the top would somehow have to become the top tube of a bike frame. And every bit of the cart would probably have to be thickened to become a bike frame able to support the weight of a human bouncing over a rough road.

The crucial evolutionary requirement is this: At every stage, with every change you make, the whole thing has to still be functional. It has to still roll. It has to still be drivable or take-to-the-store-able. Otherwise, the cart or hand truck would die out. If at any point it didn't roll, or couldn't be steered in some fashion, or if there were no practical way to keep it in balance, you'd have to abandon it. You'd just leave it by the side of the road to rust to dust, and try again with one of your other related designs. Inevitably, you'd have to keep a lot of the original design and make changes in an incremental way. That's how things are in nature, where there is no deliberate designer who can take things apart, redesign them, and put them back together if they don't work. Instead, every step has to be “good enough.” Every generation has to survive lest that species or type of organism will disappear from our world.

That is why giraffe necks are so similar to our necks and to dog necks and to horse necks. If we look closely, our necks are similar to fish necks. We are descendants of a common ancestor way back in Earth's history. Configuring necks this way is almost certainly not how a designer or engineer would build the world. But the details all make perfect sense once you embrace the idea that evolution does not work the way a human designer or engineer would.