Lamarckian Evolution is Making a Comeback

In the introduction I make the statement, “I also learned how correct Jean-Baptiste Lamarck, the famous French biologist, was for all the wrong reasons.”

Lamarck was an accomplished biologist living in the late 18th and early 19th centuries. He was an expert in the taxonomy of invertebrates, and was widely regarded as a botanist. He also wrote about physics, chemistry and meteorology.

He is best remembered, however, for his publication of Philosophie Zoologique in 1809 in which he lays out his theory of evolution. In the book, he outlines two laws of nature. The first is that animals develop or lose physical traits depending on usage of those traits. For example, if an animal like a mole always lives in darkness, then they would, over generations, become blind. Through usage, characteristics of an animal are either enhanced or decay during a lifetime. The second law states that these acquired changes during a lifetime are passed on to offspring, i.e. inherited. These two laws explain how species evolve by continual adaptation to their environment and eventually branch off into new species once the changes become large enough. This is often referred to as Lamarckian evolution.

There were other interesting aspects of his theories. He believed that there was some natural force that drove organisms toward increased complexity quite apart from the usage law. The wide variety of organisms found in nature was because different life forms appeared spontaneously at different times. Thus they do not all evolve from a common ancestor. When gaps seemed to appear in the fossil record in certain lineages, he attributed that to a failure in finding all the relevant fossils. His theory clearly assumed gradual and continual evolution, but that evolution was always driven toward greater complexity.

Lamarckian evolution was largely debunked when the works of Gregor Mendel and others later demonstrated that inheritance occurred according to discreet rules of dominant and recessive inheritance rather than through acquired characteristics. Further discoveries in genetics during the 20th century further put the notion of inheritance through acquired characteristics to rest.

BUT, Lamarck has gotten a bit of a reprieve in the 21st century. By 2003, we had completed the Human Genome Project, which told us a lot about our genome and genes, but little about the epigenome. Since then, we’ve learned a lot. The epigenome refers to the 98% of our genome that does not code for proteins (what we traditionally call genes.) Instead, much of that huge portion of our genome has to do with the regulation of genes, largely through the coding of various types of RNA and the subsequent methylation and acetylation of DNA and histones. We have between 20,000 and 25,000 protein-coding genes.  That’s about the same number as a mouse and even a worm. And many if not most of these genes do about the same thing across a wide spectrum of animals. What makes us different from a mouse or a worm is largely controlled by the epigenome.

It turns out that the epigenome is responsive to various factors in our environment like diet and chemicals. These factors do cause changes in the epigenome, which, in turn, cause changes in the expression of various genes during a lifetime. The epigenome does not ever change the DNA sequence of a gene. The remarkable fact is that some of the epigenomic changes acquired during a lifetime are passed on to progeny through the sperm and egg! Although it is not through usage of parts of the body as Lamarck proposed, there is evidence of inheritance of traits acquired during a lifetime. One could call that Lamarckian.

Another way that acquired traits will increasingly be passed on to progeny will occur once germline genetic engineering becomes more prevalent. So perhaps Lamarck was more prescient than we give him credit for.

Lamarck was extremely accomplished and well ahead of his time. He lived long before we understood genetics and his evolutionary theories preceded those of Darwin. To some extent, he has been given a bit of a bum rap. He got some things right and some things wrong. You can say that about a lot of our great scientists. He did recognize that something changes in an individual through generations and those changes result from interaction with the environment. Darwin also theorized that individuals change from generation to generation. Neither understood that these changes first require random genetic changes. Both knew that the environment played a large role in evolution, although Darwin’s natural selection is what is generally accepted today as the driving environment force rather than usage of body components. He was wrong about the multiple spontaneous emergences of different life forms at different times, but he was correct about apparent gaps in evolutionary lines reflecting incompleteness in the fossil record.

Lets give Jean-Baptiste Lamarck his due.