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The Definitions They Are a-Changin’: Lamarck, Inheritance, and Genomes

 A snappy t-shirt can say a lot about a person, such as your sense of humour or style (or lack thereof). It can also inform others of your opinions. One such shirt I remember clearly from my undergraduate days was from a (now defunct) biology undergraduate association: A black t-shirt with six panels, showing a cartoon giraffe reaching for leaves just out of reach until the final panel, where the giraffe lay deceased. Below the panels: Darwin 1, Lamarck 0. For those in the know, this is chuckle-inducing; oh, that Lamarck.

Darwin vs. Lamarck

While the name Darwin is familiar to most, Lamarck may be less so. Essentially, while both were pioneering naturalists and theorists of evolution, Lamarck argued that acquired characteristics could be inherited, while Darwin maintained that this is not the case. When the dust settled, science and history favoured Darwin over Lamarck. Centuries later, evolutionary theory is undergoing an internal census, and the crux of the issue may not be who was right or who was wrong, but why the two figures are represented as polar viewpoints, and what we lose when this is the way science is portrayed.

The acceptance of Darwin’s theories later played out in the role of Neo-Darwinism informing how we understand evolution and genetics today. This often involves ridiculing Lamarck to the point where he becomes a punchline, much like that t-shirt does. But was Lamarck so wrong? Tabitha M. Powledge, an award-winning journalist, once wrote an excellent commentary for PLOS Blogs in 2013 on Lamarck and how his ideas may be supported in view of epigenetics. Epigenetics is the study of mechanisms that affects gene expression with altering DNA, and you can learn more about it in an earlier PLOS ECR blog post by Cici Zhang. I don’t want to delve too deeply into epigenetics here, as Powledge’s more recent piece covers the relative minefield that the topic currently inhabits. What remains to be seen is how this dogmatism oversimplifies our understanding of inheritance and evolution, as argued by some scientists such as Étienne Danchin and Denis Noble.

Redefining Methods of Inheritance

The Modern Synthesis of evolution occurred between the 1930s and 1950s, when the theories of Darwin and Mendelian genetics was combined with modern experiments and discoveries such as the method of DNA replication. As an evolutionary biologist, Danchin worked on non-genetic transmitted variation, such as epigenetic variation and ecological variance. These methods of variation complicate the narrative that Neo-Darwinism advocates, where DNA is the blueprint. In fact, this analogy is so pervasive that those who are taught it begin to become suspicious of alternative methods of inheritance. Danchin instead encourages scientists to embrace an integrated view of the Modern Synthesis that includes non-genetic inheritance.

Denis Noble attempts to tackle this monopoly on inheritance that Neo-Darwinism holds by arguing that the idolization of Darwin at the expense of Lamarck is a hallmark of this dogmatism, and is both unnecessary and destructive. It is only now, with thoughtful reflection, that we can consider that maybe Lamarck was on to something. However, is it too late to reverse the clock on Lamarck being the butt of the joke among biology students? Noble says in his essay that the goal should be to “simply to distance ourselves from the biased conceptual scheme that Neo-Darwinism has brought to biology, made more problematic by the fact that it has been presented as literal truth.”

Eventually, this discussion will move from conferences and papers into the realm of the classroom, where this “literal truth” is often championed. What remains to be seen is how long it will take for this change to occur – will an alteration to the Modern Synthesis be welcomed with open arms, or will established Neo-Darwinist acolytes cry foul?

Generalising Genomes

Now that you have a sense of how inheritance is being redefined, it should come as no surprise that the definition of genome is also being called into question. As someone whose entire PhD project is based on insect genomes, you would expect that I would be able to answer the simple question: What is a genome? If asked last week, as I often am by friends and family who operate outside of science, I would give you the standard answer and move on. “Genomes are all of the DNA that is within a cell; the genome is the blueprint that an organism is built upon,” I would say somewhat matter-of-factly. Over time, I began to accumulate caveats – I don’t study epigenetics, I don’t really look into the mitochondrial genome (the mitochondria is a maternally-inherited organelle that has its own DNA and function) – but I was fairly certain on my blueprint analogy. This analogy however comes from the same school of dogmatic thinking as Neo-Darwinism, and after reading “What is a Genome?” in PLOS Genetics, I don’t have a solid answer anymore.

In the essay, Goldman and Landweber argue that while the genome-as-blueprint generalisation may have been useful at one point in time, it may be too constrained for scientific use. The authors say a genome is not really a blueprint, but instead represents a plethora of options that an organism could become, depending on the environment, methylation, other modes of inheritance, etc. Like Danchin and inheritance, Goldman and Landweber argue for a more all-encompassing explanation of the genome. In the meantime, they offer an alternative definition of genome, “an informational entity, often but not always manifest as DNA, encoding a broad set of functional possibilities that, together with other sources of information, produce and maintain the organism,” with a caveat of their own: time will tell if this definition requires further revision.

Featured Image: Discussion of Lamarck often includes reference to giraffes, as one of his key examples of acquired characteristics being passed on is an explanation of why the giraffe has a long neck – an inner ‘need’ drove the neck to stretch longer and longer with each generation until the tree canopies were reached. The image belongs to Steven Gerner (@sgerner on Flickr) and is used under a Creative Commons CC by-SA 2.0 license.

References

Danchin, Étienne. 2013. “Avatars of Information: Towards an Inclusive Evolutionary Synthesis.” Trends in Ecology and Evolution 28 (6): 351–58. doi:10.1016/j.tree.2013.02.010.

Goldman, Aaron David, and Laura F Landweber. 2016. “What Is a Genome ?” PLOS Genetics 12 (7): e1006181. doi:10.1371/journal.pgen.1006181.

Noble, Denis. 2015. “Evolution beyond Neo-Darwinism: A New Conceptual Framework.” The Journal of Experimental Biology 218 (Pt 1): 7–13. doi:10.1242/jeb.106310.

Online Resources

Powledge, Tabitha M. 2013. “Microbe Counts and Transgenerational Epigenetics” PLOS On Science Blogs. Published December 13, 2013. <https://blogs.plos.org/onscienceblogs/2013/12/13/microbe-counts-and-transgenerational-epigenetics>

Powledge, Tabitha M. 2016. “That Mukherjee piece on epigenetics in the New Yorker” PLOS On Science Blogs. Published May 13, 2016. <https://blogs.plos.org/onscienceblogs/2016/05/13/that-mukherjee-piece-on-epigenetics-in-the-new-yorker/>

Danchin, Étienne, personal website. <http://www.edanchin.fr/?lang=en> Accessed August 8, 2016.

Wikipedia contributors, “Charles Darwin,” Wikipedia, The Free Encyclopedia. <https://en.wikipedia.org/w/index.php?title=Charles_Darwin&oldid=730582014> Accessed August 8, 2016.

Wikipedia contributors, “Jean-Baptiste Lamarck,” Wikipedia, The Free Encyclopedia. <https://en.wikipedia.org/w/index.php?title=Jean-Baptiste_Lamarck&oldid=731637119> Accessed August 8, 2016.

Wikipedia contributors, “Denis Noble,” Wikipedia, The Free Encyclopedia. <https://en.wikipedia.org/w/index.php?title=Denis_Noble&oldid=729976975>Accessed August 8, 2016.

Wikipedia contributors, “Modern evolutionary synthesis,” Wikipedia, The Free Encyclopedia. <https://en.wikipedia.org/w/index.php?title=Modern_evolutionary_synthesis&oldid=731652378> Accessed August 8, 2016.

Wikipedia contributors, “Neo-Darwinism,” Wikipedia, The Free Encyclopedia, <https://en.wikipedia.org/w/index.php?title=Neo-Darwinism&oldid=728863149> Accessed August 8, 2016.

Zhang, Cici. 2016. “On epigenetics: We are not just our DNA” PLOS ECR Blog. Published March 11, 2016. <https://blogs.plos.org/thestudentblog/2016/03/11/epigenetics/>

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