WILLIAM PROVINE: Darwin's theory of evolution was truly revolutionary. But it wasn't the first theory of evolution, nor was it the first to include a proposed mechanism for descent with modification.
In 1809, the same year that Darwin was born, the French naturalist Jean-Baptiste Pierre Antoine de Monet, de Chevalier de Lamarck published Philosophie Zoologique. In it, he presented a theory of evolution that included two driving forces, a natural tendency towards increasing complexity and an adaptive force powered by use and disuse. A familiar example of this adaptive force is the idea that giraffes develop longer necks as the result of stretching to reach leaves at the tops of trees. Giraffes that stretch their necks reach more leaves and could consequently have more offspring, to whom they passed on their stretched necks.
Central to Lamarck's theory was the idea that evolution was a progressive process, moving towards ever greater complexity and ever greater perfection of adaptations. Lamarck's theory, in other words, included both a theory of descent with modification and a theory for the acquiring of adaptations of those characteristics of organisms that seemed to fulfill some kind of purpose. Lamarck's theory is most often mentioned in the context of a failed theory. This is simply not true.
Lamarck's theory was both very useful and also revolutionary for its time. Lamarck was really the first naturalist to propose a comprehensive theory of evolution and definitely the first naturalist to propose a testable mechanism by which evolution had occurred. Although many other naturalists over the past 2,000 years had proposed something like evolution, Lamarck was the very first naturalist to propose a mechanism that could be applied both to descent with modification and to the origin of functional adaptations.
Furthermore, Lamarck did something that no one else had done before. He proposed an observable mechanism by which evolution had occurred, the inheritance of acquired characteristics, especially as the result of use and disuse. Lamarck's theory therefore not only proposed that evolution had happened, it also included an explanation for the origin of evolutionary adaptations. That is, Lamarck proposed a mechanism whereby characteristics that appear to have a purpose in the life of the organism could evolve.
Adaptations are characteristics of living organisms that answer the question, what is it for? If you ask what is the long neck of a giraffe for, almost anyone who has watched a giraffe forage for food would answer, giraffes have long necks in order to eat the leaves at the tops of trees. That little phrase, "in order to," is the tip-off that one is dealing with something that has a purpose. Things that happen or that exist in order to do something are things that are designed to bring about some goal, some final end state.
In Aristotle's terminology, the goal of an adaptation is its final cause. In other words, an adaptation is a characteristic of a living organism that has a function in the life of that organism. And one can identify a characteristic as an adaptation because it appears to have a purpose. Lamarck was very clear in Philosophie Biologique that the concept of purpose was central to biology, including evolutionary biology. He believed that natural history involved not only answering the question what and how, but also the question why.
What questions ask for a simple description of something, such as the long necks of giraffes. For almost two millennia, natural history consisted almost entirely of descriptions, of answers to what questions about nature. How questions ask for much more. They ask for an analysis of how something works. Answering a how question about living things involves all the disciplines we now associate with the science of biology, anatomy and physiology, biochemistry and molecular biology, cell biology, genetics and development, and ecology.
But that still leaves the why questions about nature. Why do giraffes have long necks? Lamarck, like most biologists, explained the long necks of giraffes by saying, giraffes have long necks in order to reach the leaves in the tops of trees. That is, Lamarck believed that the answers to why questions about nature necessarily included some kind of purpose. And indeed, saying that giraffes have long necks in order to forage in the tops of trees sounds perfectly reasonable to most people, including most biologists.
We have already noted that at least since the time of Newton, physical scientists have restricted their explanations for natural processes to material and efficient causes only. For example, I've already told you how this rock has a material cause. It's made out of limestone. In an an efficient cause, the process by which the limestone was made. However, we could also apply final cause logic to this rock.
I could drop it, for example. And then say, the rock falls in order to reach the ground. To most people that explanation sounds odd. Physical processes don't happen for purposes, at least as far as we can tell. They simply happen. Rocks don't fall in order to reach the ground. They simply fall.
A force causes them to fall. And that's the end of the explanation. We explain the movement of dropped rocks by referring exclusively to causes and effects, not to purposes. But it does sound reasonable to say, for example, that giraffes have long necks in order to reach the tops of trees.
What's the difference between saying that rocks fall in order to reach the ground, which sounds odd, and saying giraffes have long necks in order to reach the leaves at the tops of trees, which doesn't sound odd at all? It seems then that biological processes, unlike physical processes, do indeed have purposes. As we will see in the next part of this series, one of the reasons that Darwin's theory is so important to the modern science of biology is that, according to Darwin's theory, purpose is not necessary to explain either descent with modification or the origin of evolutionary adaptations.
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Published 150 years ago, Charles Darwin's
On the Origin of Species provided the foundation for the modern science of biology. It also set in motion a revolution in the sciences and in our understanding of ourselves and our place in nature.
This CyberTower Study Room is a brief introduction to Darwin's theory and its implications. Beginning with an overview of Darwin's predecessors, we learn how Jean Baptiste Lamarck set the stage for Darwin's monumental achievement with his Philosophie Zoologique, which advanced a theory of evolution by means of the inheritance of acquired characteristics.
Darwin, whose academic training at Cambridge University was in Anglican theology, became an acclaimed naturalist and science writer following the five-year voyage of HMS Beagle. Using the notes and specimens that he had collected during the voyage, Darwin spent twenty years refining his theory, first published in 1859, of evolution by natural selection.
In the last segment of this Study Room, we visit the Museum of the Earth in Ithaca, New York, whose director, Dr. Warren Allman, discusses the importance of such museums to the science of evolutionary biology. We also hear from Cornell professor William Provine, who discusses Darwin's work and its importance to the history and philosophy of biology.
This video is part 3 of 6 in the Darwinian Revolutions series.