Undeniable (23 page)

Are we the only organisms around here that have this sense—a sense of doom? It sure seems like it. I spent a great deal of time in the Pacific Northwest watching and swimming with salmon. When it's time for them to head upstream to mate, they stop eating. They get their chemical energy, their food, by digesting themselves from the inside out. They essentially eat their own intestines on the way upstream to their deaths. Do salmon know that they are going to die as they head upstream to lay eggs or deposit sperm? Or, are they like a teenage boy driven by sex, sex, sex?—they can't think, or they actually
don't
think, of anything else, not even food. Or are salmon aware of their impending end of life, and are they sad? I must say it just doesn't seem like it. They swim; they mate; they die. It doesn't seem like there is a lot else going on with them.

Apparently, our closest relatives, the chimpanzees, suffer a few days of depression or mourning, when a member of their troupe or barrel dies. Do they perform rites associated with the death of a colleague or mate? If they do, I am skeptical that they take it as seriously as humans do.

But humans?! We go nuts. We construct all sorts of systems to reassure ourselves that there is more to it than swimming, mating, and dying. We deposit our writings and musings in libraries. We build statues to people whom we admire, so that at least in one sense these people live on, or their memory does. Heck we name buildings, highways, and mountains after certain people. We keep letters of deceased ancestors. We erect grave markers. All of these things, in some way, preserve a life, or at least a life's work.

It seems that we really are special, so why shouldn't there be something special waiting for us on the other side of Cowboys' Stadium? But when we're waning, when we're dying, it's not obvious that our minds are anything more than a product of an exquisitely complex system of chemical structures and chemical reactions. I remember well my grandmother talking with me about wildflowers. She had an extraordinary memory, and she had done quite a bit of artwork that included pastoral scenes of New England and a great many flowers with a naturalist's attention to detail. She spoke to me about pollen, pistils, stamen, and ova. I remember a few conversations about baseball. She listened to it on the radio, sometimes with remarkable attention to detail. She would comment on Don Mattingly's swing, even though she couldn't see it. She just thought about what she heard and where the ball went, and so on. Toward the end of her life, though, her amazing mind slipped away. She became incompetent with regard to baseball, wildflowers, the delicate control of her artist's pencils, and just about everything else.

I worked closely with Bruce Murray, a planetary scientist at the Jet Propulsion Lab (and founder of the Planetary Society) who had a tremendous influence on the United States' space program. He insisted that the early space probes should have cameras on them, and is largely responsible for the first pictures humans ever captured of the planet Mars. Toward the end of his life, Bruce could tell you a great deal about those heydays, but he could not remember whether or not he had had lunch, let alone what he had had for lunch. It's heartbreaking. At the Planetary Society we honor him by naming our collection of pictures and videos the Bruce Murray Space Image Library. His loss of memory is evidence of the chemical construction of our evolutionarily built, good-enough brains. Despite many human beliefs about an afterlife, it sure seems as though these remarkable people did not have their consciousness transported to some wonderful eternal place of rest and contemplation. Instead, it seemed as though they lost their faculties as certain systems in their bodies shut down.

Blame evolution for this unsettling conflict between the way the world works and the way we wish it would work. The fear of death, combined with a novel ability to envision the future, enabled humans to outcompete other species. But that combination also makes us unable to believe that what we see around us is all there is. Our brains got too big to think about the world any other way.

I guess the question of whether or not we're special is another way of asking, what's the point of our having big brains? Diligent paleontologists and archeologists have combed hills and valleys looking for earlier versions of us. Researchers have found dozens of bones and skulls that once belonged to our distant, distant relatives. As we study these other humanlike almost-people, we realize that they were almost like us. As we examine our recent humanlike ancestors like Neanderthals, or Cro-Magnon, or other humanlike ancestors, it becomes clear: If these guys and gals were dressed like us, you'd hardly notice them on a busy sidewalk. It just seems as though they were almost like us. Their brains were almost like ours. They almost embraced the same worldview that we have with the same suspicions or beliefs about a life after death.

It looks like we came out with the most versatile brain, which could throw, catch, and hit balls—and invent the rules of games involving balls, better than they could. It looks like these same brains gave us the ability to wonder about our place in the scheme of things, and that led us to science, and that led us to the discovery of evolution. We are products of evolution and as such, we can't believe it's all over, when it's all over.

It is a great irony of the evolution of the human brain: Our strength is also our weakness. Our asset is our liability. Through millennia of refinement, we have the ability to recognize patterns better than any other organism out there. Sure, monarch butterflies head south, when it's the right time of year. Deciduous trees shed leaves, as the days get shorter. They sprout new ones, when their internal chemical clock says it's time to. But no organism out there creates calendars with leap years. No organism out there launches rockets that go into space and back, boosted and directed by chemicals and physics. I can imagine, though, another tribe that could almost do these things. It was just that we recognize patterns a little better, so we beat them to the best food sources and shelters. And now, we're left with these brains that can make us crazy.

Which brings me back to Ken Ham and his belief, widely shared among his followers, that Earth is only 6,000 years old. When I debated Mr. Ham, I talked a lot about the geological evidence that Earth is far, far older. But for my opponent, the debate was not about the testable age of our planet. For him, it was about evolution. For him, it was about the apparently irreconcilable discrepancy between what our brains can observe along with the knowledge we can acquire and store, and the discovery that we got to this exalted state through the same process that makes some finch beaks short and sharp and others long and tapered. He just cannot believe it.

I sympathize with the troubling nature of the shortness of our lives, but a relatively short life is what we each have in store. Wishful thinking cannot change the facts, but scientific thinking can place them in a greater context. Human mortality can get you down and make you want to listen to old country western songs about how miserable life can be—or it can fill you with joy.

We have found out at least one, nearly incredible, truth about how we all got here. The astonishing thing about nature and the universe is that we can understand any of it. We humans have been around in our present form for nearly 100,000 years, yet almost everything we know about evolution has emerged in just the past 150 years. Think what lies ahead for our species, if we preserve biodiversity and raise the standard of living for everyone. We will make discoveries that would have astonished my grandmother, my colleague Bruce, and you and me today.

 

23

MICRO OR MACRO—IT'S ALL EVOLUTION

To understand evolution, we need to think both big and small. It's a recurring theme in evolutionary research, going back all the way to Darwin and Wallace. When I was a full-time engineer, I worked on drawing boards for huge airliners at one company and microscopic instruments at another. Down in the lower right of virtually all engineering drawings, there's a box where I, as the designer, indicated the scale of the picture. At Boeing, I drew at around 1 inch to represent 100 inches, 1:100. At Sundstrand, it was 1 inch to represent 0.010 inches, 100:1. It still fascinates me that the physics worked at every scale. A hydraulic actuator powerful enough to move a house is subject to the same laws of nature as a tiny spring that can detect the gravity of the Moon.

When it comes to evolution, we need to consider the big picture and the small picture. Nature affects every individual, but the effects of natural selection become apparent on the large scales: on groups, populations, species, and whole ecosystems. Researchers have coined the terms
microevolution
and
macroevolution
to describe the different ways in which evolution can unfold, though both are guided by the same fundamental principles that lead from micro to macro. Today, especially in the U.S., there are creationists who indoctrinate people to think only of the small picture. They accept the micro but reject the macro, because micro is all that their faith can accept. It's sad, and it's not science. The natural world is a package deal; you don't get to select which facts you like and which you don't. And in this case, you can't understand one kind of evolution without the other.

In its original form, Darwin's natural selection describes what happens to an organism once it is in the environment. For us, the process kicks in once we're born. For a plant, it would be once the seed is out there. For a fish, it would be once her (and his) eggs are deposited. Each new generation may be able to exploit its world's resources or not. It may get lucky and come upon plentiful resources, chemical energy for bacteria, a nice wetland for a frog. You are born with a set of genes copied from your ancestor or ancestors. Being able to keep warm, or cool, or digest the food resources around you, these are the forces of selection. There are other ways things can change from generation to generation, however.

Whether you get eaten or killed (get unselected) before you reproduce (get selected) is a huge driver of genetic change. But your genes can also be different from those of your parents just through random mutation, which is the imperfect copying from one strand of DNA to another. It can literally be a cosmic ray from outer space that knocks into one of your genes and changes it. Genes sometimes jump from one place on the DNA molecule to another. These are called transposon genes. It could be that your parent's eggs or sperm (or a plant's ova and pollen) got messed with a little by some chemical. It could be radiation from some radioactive elements in Earth's crust that caused a mutation. Sometimes viruses get into the reproductive cells of an organism and modify its genes. Virus manipulation can also be exploited deliberately—to adjust the genes of corn plants so they are tolerant of aggressive weed killer, for example.

With the little changes that happen with reproduction, the configuration of your DNA and your genes can change for you and others in the population of your kind. This is called “genetic drift.” If the genes drift a little at the same time that there's a change in the environment, the drifted genes may be the only ones that make it through. This is an example of microevolution—a change in the genetic mix within a species or population. You can think of it simply as evolution by small changes over short times.

Another source of change is the random variation that is amplified in small populations. Consider a bag of Halloween candies, where half of the candies are orange and the other half are brown. Reach in the bag and take out a handful. In general, the smaller the sample you grab, the greater the chance that it won't be an even mix. If you grab five candies, you might have three orange and two brown. That would be a 20 percent discrepancy favoring orange. On the other hand, if you were able to grab five hundred, whatever unevenness was in the mix would be smoothed out. Your ratio of orange to black would be much closer. You would seldom have such a large 20 percent difference. In the case of genes in nature, if something happens in the environment that leaves you stuck with only a small handful of individuals, the equivalent of a small handful of candies, from that moment on your uneven mix will be favored. It will be the set of genes that gets carried on. Since in this case, we are only considering one species, evolutionary researchers often refer to this, too, as microevolution.

Along this line, let's say there's a favorable mutation in a population, such as a slightly darker skin pigment that provides better protection from ultraviolet light from the Sun (which happens now and again). People with that mutation might do well and reproduce more often in places with a lot of ultraviolet exposure. That favorable darker skin gene will preferentially show up in their kids and grandkids and great-grandkids. Because it's so important to human cultures, I've devoted all of chapter 32 to this phenomenon. Researchers call this “gene flow.” The gene flows out into the population, albeit over successive generations. Since we're just talking about one gene in one organism, researchers often describe this as microevolution, as well.

In contrast, we have macroevolution: sexual, artificial, and natural selection writ large. Instead of considering one gene in one organism, we are now looking at sweeping species changes caused by shifts in the environment or by mass extinction events. The processes of microevolution and macroevolution are fundamentally the same, only the scale is different. We can study individual genes, a sequence of chemicals along an organism's DNA molecule. Or we can study a population of organisms, or an ecosystem full of organisms. They get passed on or eliminated by the same rule: If you fit in, whether as a gene or as a whole
Tyrannosaurus
, you'll get carried on. If you don't, you won't.

This distinction between micro and macro is useful for evolutionary biologists. Where it's been troublesome for me as a science educator is with the creationist community. As I learned firsthand from my debate with Ken Ham, an especially committed gentleman, creationists will seize on anything they see, or claim they see, as a loophole in evolutionary science. Mind you, finding flaws in a scientific theory is a noble business. It's a crucial part of the process by which science advances. But it requires honesty and consistency, and I don't see much of either in the creationist arguments.