Biological Evolution and the Kinship of All Life
Dr. Sean B. Carroll is a professor of genetics, molecular biology, and medical genetics at the University of Wisconsin-Madison, and a researcher and vice-president for science education at the Howard Hughes Medical Institute. He is a leader in the field of evolutionary developmental biology, or “evo devo,” and is the author of Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom (W. W. Norton, 2005).
Dr. Jeff Hardin is chair of the department of zoology at the University of Wisconsin. He is the senior author of World of the Cell (Pearson Education, 2015).
Dr. Neil Shubin is the Robert R. Bensley Professor of Organismal Biology and Anatomy, associate dean for academic strategy, and a member of the Committee on Evolutionary Biology at the University of Chicago. He is the author of Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body (Knopf Doubleday, 2008) and The Universe Within: Discovering the Common History of Rocks, Planets, and People (Pantheon Books, 2013).
Dr. Neil Shubin: There is something incredibly beautiful about seeing the past, finding a fossil, and being one of the first humans on the planet to hold this piece of history of our planet. But there’s a beauty that lies even deeper, because if you know how to look, you can begin to see connections. You can begin to see connections among humans and one another, among humans and other species, and between humans, other species, and the planet itself. The only reason that is possible is because we share an evolutionary connection with them.
Dr. Jeff Hardin: Evolution, simply put, is the change of organisms over time. These changes suggest that if we were to go back in time, we would be able to see that current organisms have some shared common ancestor in the past.
Dr. Neil Shubin: The Earth’s a dynamic place. The more we study biology, the more we study paleontology and geology, the more we see that everything on our Earth is capable of changing, and that includes the species on it.
Dr. Sean B. Carroll: I don’t think the terms evolution and Darwinism should be interchanged. Darwinism is a left-over term from a 19th Century…but evolutionary science has grown enormously in the 150 years since Darwin. So, I think it’s just better to refer to it as evolutionary science in all of its stripes.
Our understanding of evolution has expanded in the most dramatic ways in the last 30 or 40 years I’d say in two dimensions. One is the mechanisms. Changes happen in creatures because of changes in DNA. Well, that was just outside Darwin’s grasp. It wasn’t until the 1960’s that we cracked the genetic code. It wasn’t until the subsequent decades that we could really start looking at different creatures and say, “Well, they differ here versus there in the genetic code.” So really, DNA is a forensic record of evolution. It’s where all the blueprints, it’s where all the important changes are taking place.
Dr. Jeff Hardin: The key idea is that genetic material changes through mutation. How mutations occur in an organism has nothing to do with desires or its fitness or its own adaptation. There’s no obvious connection between that organism’s life and the particular mutation it acquires.
Dr. Sean B. Carroll: Here’s the random process. As DNA is replicated in germ cells making sperm and egg, there are random copying errors that take place, these typos, substitution of a letter, little deletions, et cetera. Where those occur in the DNA is essentially at random. So, that’s the raw material that evolution is working with. That’s random. The nonrandom part is this sifting and winnowing process, which is now that you have a population of individuals with all these random mutations distributed throughout, who works better? Who just does a little bit better in terms of maybe getting to food, finding a mate, producing offspring, or whatever it might be? That’s a nonrandom process.
That depends upon the conditions that an organism is confronted with. That’s natural selection. Natural selection works both ways. It works for things that are beneficial, and against things that are harmful, not random. The variations themselves have arisen at random. It’s that interplay between random and nonrandom natural selection that is the evolutionary process. That’s the machinery.
The second big change in our understanding of evolution is the fossil record. Darwin, when he wrote The Origin of Species, he said, “The crust of the Earth is a vast museum that’s barely been explored.” Well, we’ve been exploring that crust for the last 150 years, and great stuff is coming out of there.
Dr. Neil Shubin: When you’re a paleontologist, one of the greatest thrills is, from time to time, you’ll find a species in the fossil record that bridges two great steps in evolution. What this represents is a great transition between fish and land living animal. This is a creature that has fins with limb bones inside. It shows us how this huge transition that if you just look at the end points, seems so incredibly impossible happened. It makes the impossible possible. It makes the impossible real.
Dr. Sean B. Carroll: Whether it’s feathered dinosaurs out of China or a dozen different Hominid species coming out of Africa, we keep finding new things that existed in the past that give us yet a fuller picture of the history of life on Earth.
Dr. Jeff Hardin: It’s important to say that evolutionary biologists don’t all agree to what extent evolutionary history is contingent. That is to say, if you were to wind the tape of history back and replay it forward, would you get a very different result or would you get something remarkably similar to what we have now?
Dr. Neil Shubin: Would everything be the same? Would there be a bipedal, hairy, warmblooded species with big brains walking around? We simply don’t know the answer to that, but there are some interesting little data points along the way. One interesting observation is convergence and parallel evolution. That is, we sometimes see similar patterns of evolution in unrelated creatures.
Dr. Jeff Hardin: The eye is an example of convergence. The structures in eyes that things like squids or octopi have and mammals have are remarkably similar, yet they’re derived from very different structures over evolutionary time, so we’re converging on a particular solution.
Dr. Sean B. Carroll: I don’t think you would see exactly the same creatures emerge because there’s a tremendous amount of contingency in history. The easiest way to think about that is a pretty good sized asteroid hit the world 66 million years ago, and that really changed the makeup of life on the planet. That said, biologists are struck that similar types of creatures can evolve independently in different parts of the world.
Dr. Jeff Hardin: It’s clear there is contingency in evolution, but to what extent is contingency the order of the day versus convergence? Well, evolutionary biologists are working that out. Understanding our evolutionary history helps us understand who we are today. Evolutionary biology has incredible value for understanding how humans work.
Dr. Sean B. Carroll: I think the discussion that’s really interesting between religious thinkers and scientists is getting over this question of, “Did evolution really happen?” The more interesting question is how should we think about the role of humanity, the role of individual lives and our meaning and purpose here in light of evolution, in light of our evolutionary history?
Dr. Neil Shubin: When we look at other critters, we understand much more about ourselves. We understand how our cells work, how our cells divide, how they die. The trick of understanding much of cancer and some of the cell biology of cancers means understanding other creatures. I like to think that as we discover cures, from Alzheimer’s to different cancers, that the breakthroughs that will extend and enrich our lives will in some way be based on flies, worms, and, in some cases, even fish. I can’t imagine a more powerful or more beautiful statement on the importance of our evolutionary connection to the rest of life on our planet than that.
- Course Categories: Biblical Studies, General Theology
- Science Topics: Earth Science & Environment, History & Philosophy of Science, Life Sciences
Darwinism, Biological Evolution, science and religion, Dr. Jeff Hardin, paleontology, Dr. Neil Shubin, kinship of all life, common ancestor, DNA, human evolution, Dr. Sean B. Carroll