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Updating Darwin: biologists are returning to an…

Science · July 30, 2026 · The Conversation · 6 min

To make sense of some characteristics that species exhibit from birth, you have to turn to an old discredited theory known as Lamarckism.

<a href="https://theconversation.com/profiles/pim-edelaar-2601235">Pim Edelaar</a>, <a href="https://theconversation.com/institutions/lund-university-756">Lund University</a>; <a href="https://theconversation.com/institutions/universidad-pablo-de-olavide-1362">Universidad Pablo de Olavide</a>

Evolution is a fact of life. So much so that even the theory of evolution is evolving. Lately, a centuries-old discredited idea has been making a strong comeback. It helps us explain scientific observations that according to standard evolutionary theory should be impossible.

<figure class="align-right zoomable"> <a aria-label="Zoomable image" href="https://images.theconversation.com/files/749999/original/file-20260724-101-1aoayb.jpg?ixlib=rb-4.1.1&q=45&auto=format&w=1000&fit=clip"><img alt="Portrait of Jean-Baptiste Lamarck" src="https://images.theconversation.com/files/749999/original/file-20260724-101-1aoayb.jpg?ixlib=rb-4.1.1&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/749999/original/file-20260724-101-1aoayb.jpg?ixlib=rb-4.1.1&q=45&auto=format&w=600&h=757&fit=crop&dpr=1 600w, https://images.theconversation.com/files/749999/original/file-20260724-101-1aoayb.jpg?ixlib=rb-4.1.1&q=30&auto=format&w=600&h=757&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/749999/original/file-20260724-101-1aoayb.jpg?ixlib=rb-4.1.1&q=15&auto=format&w=600&h=757&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/749999/original/file-20260724-101-1aoayb.jpg?ixlib=rb-4.1.1&q=45&auto=format&w=754&h=952&fit=crop&dpr=1 754w, https://images.theconversation.com/files/749999/original/file-20260724-101-1aoayb.jpg?ixlib=rb-4.1.1&q=30&auto=format&w=754&h=952&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/749999/original/file-20260724-101-1aoayb.jpg?ixlib=rb-4.1.1&q=15&auto=format&w=754&h=952&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a> <figcaption> Jean-Baptiste Lamarck. <a class="source" href="https://en.wikipedia.org/wiki/Jean-Baptiste_Lamarck#/media/File:Jean-Baptiste_de_Lamarck.jpg">Wikimedia</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a> </figcaption> </figure>

I’m referring to Lamarckism, named after theoretical proposals from French biologist Jean-Baptiste Lamarck <a href="https://www.cambridge.org/by/universitypress/subjects/life-sciences/evolutionary-biology/philosophie-zoologique-ou-exposition-des-considerations-relative-lhistoire-naturelle-des-animaux">in 1809</a>. Lamarckism stands for the hypothesis that parents of a given organism may acquire or improve certain characteristics during their lifetimes in response to the demands of their environment. And they then somehow transmit those characteristics to their offspring, making those better able to cope with the same demands too.

Lamarck sought to explain why organisms and their environments fit so well together, and how organisms change over time, as observed in the fossil record. Of course, an alternative explanation was <a href="https://darwin-online.org.uk/converted/pdf/1861_OriginNY_F382.pdf">provided by Charles Darwin</a> (and others) half a century later. Darwin’s ideas were built around natural selection, which says that some individuals within a species are born with differences that lead them to perform better and therefore reproduce more than others.

Darwin argued that if these differences can be passed from parent to offspring, the next generation will contain relatively more of these higher performing individuals. In other words, the next generation will have a greater fit with their environment.

Over time, Lamarck’s idea was discredited. A key moment was an experiment performed by <a href="https://identity.wellcomecollection.org/works/ax46du33">Germany’s August Weismann in 1904</a>. He surgically removed the tails of adult rats before allowing them to reproduce, expecting to see this change inherited by their offspring. But it never happened, despite him removing the tails of many generations of rats. Lamarckism as understood then would have predicted that the offspring should have been born with no tails, so for many years biology textbooks presented his theory as a firmly refuted hypothesis.

<h2>Where Darwinism falls short</h2>

Lamarck’s ideas weren’t entirely wrong, however. Take, for example, the small worm C elegans. When an adult worm is exposed to external stimuli such as viral or bacterial infections, starvation, or stressful temperatures, it can adapt to cope better over time. And, surprisingly, its subsequent offspring also cope better from the moment they are born – as do successive generations.

<a href="https://doi.org/10.7554/eLife.65797">It turns out</a> that this occurs via the inheritance of DNA-like molecules called small RNAs (ribonucleic acids). When adult worms experience stress, they produce these RNAs to fine-tune the activity of their genes to mount an effective response. When the worms reproduce, specific proteins transfer these small RNAs to their eggs, meaning the offspring are born with the benefits they provide.

<figure class="align-center zoomable"> <a aria-label="Zoomable image" href="https://images.theconversation.com/files/719935/original/file-20260223-57-q777bx.png?ixlib=rb-4.1.1&rect=0%2C0%2C1384%2C1140&q=45&auto=format&w=1000&fit=clip"><img alt="C. elegans worm" src="https://images.theconversation.com/files/719935/original/file-20260223-57-q777bx.png?ixlib=rb-4.1.1&rect=0%2C0%2C1384%2C1140&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/719935/original/file-20260223-57-q777bx.png?ixlib=rb-4.1.1&q=45&auto=format&w=600&h=495&fit=crop&dpr=1 600w, https://images.theconversation.com/files/719935/original/file-20260223-57-q777bx.png?ixlib=rb-4.1.1&q=30&auto=format&w=600&h=495&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/719935/original/file-20260223-57-q777bx.png?ixlib=rb-4.1.1&q=15&auto=format&w=600&h=495&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/719935/original/file-20260223-57-q777bx.png?ixlib=rb-4.1.1&q=45&auto=format&w=754&h=622&fit=crop&dpr=1 754w, https://images.theconversation.com/files/719935/original/file-20260223-57-q777bx.png?ixlib=rb-4.1.1&q=30&auto=format&w=754&h=622&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/719935/original/file-20260223-57-q777bx.png?ixlib=rb-4.1.1&q=15&auto=format&w=754&h=622&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a> <figcaption> The 1mm long C. elegans is one of many creatures with traits that don’t easily fit Darwinism. <a class="source" href="https://elifesciences.org/digests/38198/controlling-cell-division-with-light">Sander van den Heuvel et al</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a> </figcaption> </figure>

This is like a person receiving a vaccine against flu or measles, developing immunity in response, and then all their newly born children and even grandchildren being immune too. It was previously thought that these kinds of epigenetic molecular marks were always erased during reproduction, meaning offspring have to start their own response from scratch. The fact that acquired traits can actually be inherited is clearly Lamarckism in practice.

It’s also far from unique. There are <a href="https://press.princeton.edu/books/hardcover/9780691157672/extended-heredity">now dozens</a> if not hundreds <a href="https://doi.org/10.1016/j.tree.2021.08.006">of studies</a> showing similar effects in all sorts of species, from bacteria and plants to animals. <a href="https://pubmed.ncbi.nlm.nih.gov/40409269/">When rice plants</a> are exposed to cold, for instance, they develop a seemingly permanent resistance by adding chemical tags to their genes. This has enabled them to spread northward from their tropical origins.

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