A Biologist Looks at Intelligent Design

by David Sadava, Pritzker Family Foundation Professor of Biology, Joint Science Department

David SadavaBiology is the science of life. For centuries, biologists have tried to define what life is, and most come up with a set of characteristics:

  • Living things are chemically complex. Rather than just reflecting their environment, they can change the substances within them by rearranging the atoms. The muscle proteins we build up in the gym and the fat that we build up if we don’t go there are certainly not the same substances we eat.
  • Living things can regulate their interactions with their environment. A familiar example is the constant body temperature regardless of the weather in some organisms.
  • Living things grow and develop. Each one of us comes from a single cell, the fertilized egg. Yet by the time we are fully grown, we are made up of some 60 trillion cells, including many specialized ones.
  • Living things reproduce themselves. But the reproductive process is not perfect, as errors creep in. This produces many inherited varieties of species. Just as not all humans are alike, so too with fruit flies, bacteria, and pine trees.

Looking at the amazing variety of organisms and their activities, in creatures both alive today and in fossils that were once alive, biologists are at once awed and challenged. How can we make sense of the living world? Three ideas underlie the way biologists look at life:

  • Cell theory: All living things are made up of cells. The invention of the microscope several hundred years ago revealed a common “brick,” later called the cell that builds all life. Some living things are just one cell. Remember the microscopic amoeba in high school science class? Others, like us, have trillions of them. Cells may look different, but all have common structures, and it is inside of them that the chemistry of life occurs.
  • Mechanism: All of life can be explained in terms of the same laws of chemistry and physics that govern the rest of nature. For instance, living organisms have the same kinds of atoms — such as carbon, hydrogen, oxygen, and nitrogen — that occur in rocks, air, and the solar system. It’s the particular composition and joining of the atoms that gives life its unique constituents.
  • Evolution by natural selection: 150 years ago, Charles Darwin proposed two ideas that tie the myriad living organisms together. The first was that organisms can be related over time by common ancestry, that there has been descent with modification. The second was that over the generations coming from a common ancestor, there is an accumulation of random, inherited changes so the succeeding generations show variety. When the environment changes, some of these varieties will be advantageous to the organism for its reproductive success. In this way, natural selection leads to evolution of an organism over many generations.

While most people would sign on to the first of these three biological ideas (who can argue about the existence of cells?), they are not so sure about the next two. There has been a long tradition of belief that life is special, not totally subject to physical laws, and living things with their “vital essence” are not subject to natural selection. For example, William Paley, an English theologian used the “blind watchmaker” analogy in 1802:

“If we find a pocket watch in a field, we immediately infer that is was produced not by natural processes acting blindly but by a designing human intellect. Likewise, the natural world contains abundant evidence of a supernatural creator.”

In the twentieth century, biologists methodically unraveled complex organs like the eye. These organs were no longer mysterious, but explicable from their parts. Mechanism ruled. Biologists could explain the origin of each part of these complicated structures in terms of evolution by natural selection.

But biologists now had another way to describe life and that was in terms of its chemistry. Just as their predecessors had spent their careers looking at anatomy and function of organs and organisms, the tools of biochemistry now allowed biologists to describe such substances in cells as DNA and proteins. Progress was rapid, and applications to medicine and agriculture continued to be significant. Biologists’ excitement turned from the elaborate machines in organs to the molecular machines inside cells.

As the 20th century closed, history repeated itself. A biochemist, Michael Behe, looked at some of the molecular machines and, in 1996, pronounced himself dissatisfied with his colleagues’ mechanistic and evolutionary explanations. Instead, he revived some ideas to apply to this biological “micro world,” just as his predecessors had applied them to the biological “macro world.”

Unlike Biblical creationists, Behe did not deny the earth is very old, organisms are related by common descent, or there is evolution by natural selection on the scale of organs and organisms. Instead, he focused inside cells and said some of the intricate pathways of chemical conversions and aggregates of molecules could only be explained by “irreducible complexity” and had got there by “intelligent design.” These were certainly not new phrases!

The scientific community of biochemists responded to Behe. In numerous papers, they showed that natural selection could indeed explain the origin of the molecular machines and pathways that were the focus of Behe’s concern. An analogy to the issue at hand is the mousetrap. This simple machine has five parts: a flat platform, a metal hammer to kill the mouse, a spring to power the hammer, a catch to hold and release the spring, and a metal bar to connect the catch and hold the hammer back. You can’t catch a mouse with just a platform. You need all the parts together. There has to be a designer. But is this irreducibly complex? That is, do all the parts exist just for the mousetrap? Certainly not: all of them can have other uses.

Behe used the bacterial flagellum as an example of irreducible complexity. The flagellum is a whip-like projection that allows single-celled bacteria to swim in their moist environment toward food and away from poisons. It is clearly good for a bacterium to have one. A biologist would say that in terms of natural selection, the flagellum is selectively advantageous for survival and reproduction in these conditions. The first bacterium that had the inherited variation allowing it to form a flagellum would pass on this capacity to its off spring. Over time, this species of bacterium would evolve to all having a flagellum.

Like the mousetrap, the flagellum has several parts, all of them proteins: a propeller, a motor to drive the propeller, a universal joint to attach the propeller to the motor, a stator to hold the motor to the outer boundary edge of the bacterial cell, and bushing material to allow the motor to penetrate the cell boundary. All of these are essential; if one is missing, the thing does not work. Looking at this amazing structure, it is tempting to say it is irreducibly complex and an intelligent designer supervised its assembly.

But like the mousetrap, parts of the flagellum can have other uses. Biochemists showed the propeller protein is used by other bacteria to bind to other cells; the motor protein is used in reverse in many species to produce energy rather than use it; the universal joint protein is used in other species for the removal of substances from the cell; the stator protein is present in all bacteria where it acts as a hole through which salts can enter the cell; and the bushing protein is another molecular complex involved in killing other cells (indeed, it is involved in the plague or Black Death once attributed to supernatural forces). In short, all of the proteins in the flagellum were not put there just for that purpose. They or their cousins in other species have different functions. It is only when a random change in the inherited material of a bacterium caused the five components to come together in the same place that they assembled into a flagellum.

But having a flagellum would not be an advantage leading to evolutionary change until the environment changed and bacteria having the assembled components in a flagellum survived and reproduced better than their non-flagellum-bearing siblings. So the amazing structure of the bacterial flagellum can be explained in terms of mechanism and evolution by natural selection.

Behe proposed that several other molecular machines and pathways in the cells were irreducibly complex and could not be explained by natural selection. In each case, biochemists carefully demonstrated they could be. As the new century dawned, the matter seemed closed

But it wasn’t. Undaunted and financially supported by religious groups, Behe began a lecture tour (he has been to Claremont). His views have been used to challenge educators to teach intelligent design in the science classroom as an alternative explanation to evolution by natural selection. There have been court cases, statements by political leaders, and condemnations by scientists who thought the matter had been resolved in terms of science.

There is a deeper issue that underlies the persistence of proponents of intelligent design and irreducible complexity. One of the aims of the Center for Renewal of Science and Culture, a group that supports Behe and the idea of intelligent design, is “the overthrow of materialism and its damning cultural consequences,” and to liberate science from “atheistic naturalism.” In other words, they are worried about the mechanistic world that scientists have proposed. Biological complexity that can be explained by mechanistic natural selection removes the spiritual component from our wonderment.

Is science marching toward a mechanistic explanation for even those things that many of us regard as unique to life? If a wide variety of people were asked what distinguishes advanced animals, including humans, from the inanimate world, most would put emotions high on the list. If these are explained in mechanistic terms, we may have few places to go for a spiritual approach to life.

The vole is a small rodent that looks like a fat mouse. Two species of voles are prairie voles and montane voles; obviously, they live in different habitats. When prairie voles mate, a hormone called oxytocin is released and goes through the blood stream to the brain. When it arrives there, it binds specifically to a part of the brain that causes a behavioral change: the voles become socially bonded to one another, staying together through the birth and early life of their off spring. No such fidelity governs the post-coital behavior of montane voles. They mate, and the male soon goes on to other sexual conquests. Montane voles make oxytocin just fine, but it does not bind to the correct area of the brain. This single difference in oxytocin action is inherited. So biologists were able to isolate the chemical determinant of vole fidelity, put it into montane voles and — presto — a male and female who now made a home together.

If oxytocin is the “trust hormone” in voles, does it act the same way in humans? Some interesting data suggest it does. Humans produce oxytocin and have the binding site for it at the right place in their brains. In a clever experiment, two groups of people were given a nasal spray, but half of them got one with oxytocin. In a simulated financial transaction game, the oxytocin-exposed people trusted their money with a stranger more than their non-exposed counterparts. The implications of this for people in the business world, and even in non-business social interactions, are obvious.

The oxytocin story has broader significance. It and other stories like it are providing mechanistic and ultimately evolutionary explanations for behaviors that most humans have thought made us and some fellow animals unique in nature, and certainly distinct in some fundamental way — most would call it a spiritual way — from the non-feeling universe. Waking up in the morning to say to your partner that binding of oxytocin to the brain the previous night led to pleasant sensations of love and trust that are evolutionarily advantageous to the propagation of the species may not be the romantic world most people want. We may prefer some mystery that is ultimately not solvable by the laws of physics and chemistry. This is what the debate about intelligent design may be all about.


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