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.
Author
- Pim Edelaar
Visiting Professor, Division of Biodiversity and Evolution, Lund University; Universidad Pablo de Olavide
I’m referring to Lamarckism, named after theoretical proposals from French biologist Jean-Baptiste Lamarck in 1809 . 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 provided by Charles Darwin (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 Germany’s August Weismann in 1904 . 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.
Where Darwinism falls short
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.
It turns out 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.
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 now dozens if not hundreds of studies showing similar effects in all sorts of species, from bacteria and plants to animals. When rice plants 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.
Beyond epigenetics, the passing down of learned skills from one generation to another is also a form of Lamarckism. When killer whale mothers acquire the skill to hunt a different type of prey – for example, seals instead of salmon – this skill is copied by their offspring. This has been so reliable across generations and so profound that it even seems to have caused the formation of different species of killer whale .
Does this mean Darwinism is wrong? No, it doesn´t. Natural selection still accurately explains evolutionary processes a large proportion of the time. But as I argue in my new book , The Selective Organism: an Expanded Theory of Adaptive Evolution, we could see Lamarckian acquisition of traits as a second driver of evolution, acting alongside natural selection.
Whereas in Darwinian evolution individuals in a species are a target of natural selection, in which their traits are tested by their environment, in Lamarckian evolution they’re an agent of selection, developing certain traits out of a larger set of potential ones. For instance, the C. elegans worm could potentially produce a number of different RNA molecules (or none). Based on its environment, it selects molecules that help it to survive. In that sense, Lamarckian acquisition can be seen as a form of selection too.
How the theories combine
In my book I also make another argument. When an individual plant or animal is able to transmit acquired beneficial traits to its offspring as per Lamarckism, this should increase the offspring’s chances of survival and subsequent reproduction.
If so, this capacity should also be favoured by natural selection. In other words, Darwinism actually predicts that this Lamarckian capacity should evolve. This means that these are not competing theories but compatible ones, which together provide the best explanation for the evolutionary change of organisms.
Evolution by natural selection has been called “the single best idea anyone has ever had”. Besides explaining the natural world, it has found tremendous application in other areas. It has helped us improve how we breed plants and animals, for instance, and how we combat the evolution of antibiotic resistance in microbes.
The Lamarckian dimension should only further improve these applications. If the exposure of organisms to particular soil, climate, parasites or predators can benefit their offspring, there may be new ways to improve agricultural production. The same goes for conservation: scientists in Australia are already exposing coral to heat stress in the laboratory to trigger epigenetic responses that make them more resilient to heatwaves.
And if human parental behaviours can influence obesity or addiction in their children, then prevention programmes help not only the people that receive them but also future generations.
So after more than 200 years it is time to embrace Lamarckism again, and include it into an updated and improved version of standard evolutionary theory.
