Judgment Day: Intelligent Design on Trial

PBS Airdate: November 13, 2007
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Chapter 6

NARRATOR: Lawyers for the parents may have impressed the judge and reporters. But many in Dover wondered, "Why is evolution taught as fact if it's ‘just a theory?'"

ALAN BONSELL: Maybe Darwinism is the prevalent theory out there today, but it is a theory. It isn't a law of science. It isn't, you know, a fact. It is a theory.

BILL BUCKINGHAM: We just wanted alternative views talked about, too. We weren't, we weren't saying, "Don't talk about Darwin." Talk about Darwin, it's a theory. But that's what it is, it's not Darwin's law, it's not Darwin's fact, it's Darwin's theory.

ROBERT ESHBACH: To say it's just a theory is really a bit insulting to science because in science, a theory holds more weight than just a fact does.

KEVIN PADIAN (Dramatization): And here I think the term "theory" needs to be looked at the way scientists consider it. A theory is not just something that we think of in the middle of the night after too much coffee and not enough sleep. That's an idea. A theory, in science, means a large body of information that's withstood a lot of testing. It probably consists of a number of different hypotheses and many different lines of evidence. Gravitation is a theory that's unlikely to be falsified, even if we saw something fall up. It might make us wonder, but we'd try to figure out what was happening rather than immediately just dismiss gravitation.

KEVIN PADIAN: Facts are just the minutiae of science. By themselves, they can be right or wrong. But a theory is something that has been tested and tested over and over again, built on, revised. It continues to be reworked and revised.

ROBERT MUISE (Dramatization): Dr. Miller, would you agree that Darwin's theory of evolution is not an absolute truth?

KENNETH R. MILLER (Dramatization): Well, I certainly would, for the very simple reason that no theory in science, no theory, is ever regarded as absolute truth. We don't regard atomic theory as truth. We don't regard the germ theory of disease as truth. We don't regard the theory of friction as truth. We regard all of these theories as well-supported, testable explanations that provide natural explanations for natural phenomena.

ROBERT MUISE (Dramatization): Should we regard Darwin's theory of evolution as tentative?

KENNETH R. MILLER (Dramatization): We should regard all scientific explanations as being tentative, and that includes the theory of evolution.

NEIL SHUBIN: Science is about discovering the unknown, what we don't know. I don't focus on what we know as a scientist. I want to find new things that tell me about what I don't know.

NARRATOR: As the plaintiffs testified, that quest to investigate the unknown has led to the discovery of some of the strongest evidence for evolution.

Darwin was convinced that species evolve over time, through natural selection acting on inherited traits. But he had no idea how those traits arose or how they were passed from generation to generation.

When 20th century scientists discovered the role DNA plays in heredity, they founded a new science, called "genetics," that put Darwin's theory to the test.

Virtually every cell in every living thing contains chromosomes, which are made of densely packed strands of DNA that function as a blueprint of the individual organism's characteristics. During reproduction, chromosomes from each parent replicate and shuffle their parts to produce new chromosomes. Then, each parent passes chromosomes to offspring. But the process is imperfect. Along the way, DNA is subject to random mutations, or mistakes, giving each offspring its own unique blueprint. Sometimes this produces characteristics in offspring that are benign. Other times it produces harmful characteristics, like a misshapen wing. But occasionally, the process gives rise to a beneficial trait. For example, a butterfly whose coloration mimics another species of butterfly that tastes bad to birds.

About a hundred years after Darwin proposed that natural selection acts on new traits appearing in a population, genetics revealed the biological mechanism that gives rise to those traits in the first place.

KENNETH R. MILLER (Dramatization): And therefore you could say that when modern genetics came into being, everything in Darwin's theory was at risk, could have been overturned if it turned out to contradict the essential elements of evolutionary theory, but it didn't contradict them, it confirmed them in great detail.

NARRATOR: And, as Miller would testify, a genetics paper published less than a year before the trial had confirmed what has long been the most inflammatory part of Darwin's theory, the common ancestry of humans and apes.

That paper explored a curious discrepancy in our chromosomes. The cells of all great apes, like chimpanzees, gorillas and orangutans, contain 24 pairs of chromosomes. If humans share a common ancestor with apes, you'd expect us to have the same number. But surprisingly, human cells contain only 23 pairs.

KENNETH R. MILLER (Dramatization): The question is, if evolution is right about this common ancestry idea, where did the chromosome go? Well, evolution makes a testable prediction, and that is that somewhere in the human genome, we ought to be able to find a piece of Scotch tape holding together two chromosomes, so that our 24 pairs...two of them were pasted together to form just 23. And if we can't find that, then the hypothesis of common ancestry is wrong and evolution is mistaken. Next slide.

NARRATOR: To solve this riddle for the court, Miller would show how scientists discovered traces of our evolutionary past buried in the very structure of a chromosome carried by all humans.

Typically, on the ends of every chromosome, you should find special genetic markers, or sequences of DNA called "telomeres." And in their middles, you should find different genetic markers called "centromeres." But if a mutation occurred in the past, causing two pairs of chromosomes to fuse, we should find evidence in those genetic markers: telomeres not only at the ends of the new chromosome, but also at their middles, and not one, but two centromeres. Finding a structure like this in our chromosomes would explain why humans have one pair fewer than the great apes.

KENNETH R. MILLER (Dramatization): And if we can't find that, then evolution is in trouble. Next slide.

Lo and behold, the answer is in Chromosome Number 2. All of the marks of the fusion of those chromosomes predicted by common descent and evolution, all those marks are present on human Chromosome Number 2.

So the case is closed in a most beautiful way. And that is the prediction of evolution of common ancestry is fulfilled by that lead pipe evidence that you see here, in terms of tying everything together, that our chromosome formed by the fusion from our common ancestor is Chromosome Number 2. Evolution has made a testable prediction and it has passed.

WITOLD "VIC" WALCZAK (Dramatization): So modern genetics and molecular biology actually support evolutionary theory?

KENNETH R. MILLER (Dramatization): They support it in great detail. And the closer we can get to looking at the details of the human genome, the more powerful the evidence has become.

NEIL SHUBIN: Darwin didn't even know about molecular biology and DNA, yet that's where some of the most profound evidence is being uncovered today. Think about that. That somebody in the 1800s made predictions that are being confirmed in molecular biology labs today. That's a very profound statement of a very successful theory.

KENNETH R. MILLER: Not a single observation, not a single experimental result, has ever emerged in 150 years that contradicts the general outlines of the theory of evolution. Any theory that can stand up to 150 years of contentious testing is a pretty darn good theory, and that's what evolution is.

NARRATOR: And the deep understanding of evolution as proposed by Darwin has, with genetics, unlocked many of the secrets of life.

ROBERT PENNOCK (Michigan State University): It's an explanatory framework within which all the rest of biology fits. It's something that we use in practical biological applications: medicine, agriculture, industry. When you're getting a flu vaccine—that really depended upon evolutionary knowledge. In many, many specific ways, evolution makes a practical difference. It's not just something that happened in the past, evolution's happening now.

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