Lamarckism, The First Theory of Evolution

These are the slides from a lecture I gave on Lamarckism last week, along with explanatory text. It goes through the intellectual precedents of Lamarckism, an explanation of Lamarckism, how it fares against natural selection, and an outline of its history. Here’s a PDF version.

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Lamarckism may have been the first comprehensive theory of evolution, but it wasn’t invented out of thin air by Lamarck. As with any theory, it’s founded on thoughts and principles already found in scientific circles of the time. With Lamarckism, the two most important pre-existing thoughts were the idea of the scala naturae, and the idea that species could change in different environments.

The scala naturae, the “great chain of being”, is an idea that can be traced back to Aristotle and probably before, and is basically a hierarchical classification system whereby those at the bottom of the hierarchy are the simplest organisms and those at the top are the most complex. Imagery based on it is still way too common and its influence is still pervasive in bad evolution popularisation – the ideas that evolution has a direction or that humans are the pinnacle of evolution are direct descendants of the scala naturae. The classical scala naturae is fairly similar to that presented on the right: the four elements at the bottom, then metals, salts and rocks, then mosses and plants, then insects, then seashells, then reptiles, then fish, then birds, then quadrupeds, then humans. In less scientifically-minded texts, humans would be followed by angels and, of course, God.

Scala naturae source: Bonnet C. 1745. Traité d’Insectologie.Vol. 1.

Ideas that species could change somehow were quite common in the early 19th century – this was not Lamarck’s breakthrough. For example, Buffon, his mentor, pioneered his own ideas about this, although all these concepts were rather vague.

img2Lamarck himself had a somewhat torturous road to academia, having served well in the army before being discharged, and going on to study four years of medicine before being dissuaded by his brother. He became an understudy of leading French naturalist Bernard de Jussieu, concentrating on botany and, in 1978, publishing a three-volume compendium of the French flora that was impressive enough to attract Buffon, who took him under his wing and got him a position at the French Academy of Sciences and the royal botanical gardens. The aftermath of the French Revolution was a reforming of the gardens into the National Museum of Natural History in 1793, in which he gained the position of invertebrate professor (despite this not being his specialty), a position he held until his death.

Biographical information aside, Lamarck is most famous for Lamarckian evolution (although, as we will see, what we nowadays call Lamarckism is actually neo-Lamarckism). Besides this, we take many of his advances for gratned – the word “biology” is his invention, as are the now-ubiquitous systematic categories of “vertebrate”, “invertebrate”, “insect”, “crustacean”, “arachnid”, “echinoderm”, and “annelid”. So do not think that he’s just some wacky naturalist of the past who is now completely discredited: some of his work does still live on.

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Anyway, our topic here is Lamarckism, his milestone idea about evolution that he outlined in three of his publications. He first came to think about such things while sorting through Bruguière‘s collection of fossil and extant molluscs at the Natural History Museum – he was the previous curator of invertebrates and died. Lamarck realised that the fossil molluscs and the extant ones are analogous, and by plotting their distribution in time, he could trace a direct lineage from the ancestral species to the recent ones. This triggered the rest of the thoughts, which he first exposed in his 1801 book, Recherches sur l’Organisation des Corps Vivants.

But the real explanations details of the evolutionary process came in what is considered his magnum opus, 1809’s Philosophie Zoologique. 1815 saw the release of the first volume of his new invertebrate textbook series, Histoire Naturelle des Animaux Sans Vertèbres, where he also provides a summary of Lamarckism.

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I already said that Lamarck was highly-influenced by ideas already floating around, especially that of the great chain of beings. Lamarckism takes the idea of progression as its first core foundation – organisms can be classified from simplest to most complex, and evolve in that direction.

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However, Lamarck went further than his contemporaries by trying to postulate a mechanism for this progression, rather than taking it for granted. He proposed that animal life has some sort of endowment built into it, an inherent ability to become more complex, and that would explain the presence of a natural hierarchical classification.

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This natural complexification can thus best be pictured not as a climb up a ladder, but by the species staying static on an escalator. The axis naturally carries the species up an axis of complexity – it’s just a matter of time for the species to transform from a simple morphology to a complex one.

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But if you think about it – as Lamarck did, of course – you would realise that there is a theory-breaking problem with this proposition of an automatic, linear progression. It’s the classic creationist argument: if we evolved from monkeys, why are monkeys still around? If this is a linear progression, then they should already be human.

This is solved by saying that biogenesis – the formation of new life – is constantly happening. In other words, there are many escalators (one for each category of life), and each one represents a different starting point. Humans are the oldest organisms, and “worms” (they still lumped the Vermes all together back then) are among the youngest, given their apparent simplicity.

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But there is also a second problem, one of scale. A hierarchical classification that goes something like worm-fish-reptile-bird-mammal-primate-human can be somehow justified by the standards of of the day.

Now pick one category from those, the mammal for example. You have rodents, bats, canids, felines, cetaceans, ungulates, pinnipeds. Making a sensible hierarchy out of these may be possible.

Now choose on ofe these categories, for example the felines. You have house cats, bobcats, ocelots, lions, tigers, pumas, leopards. At this point, making a hierarchy becomes an exercise in senseless futility, and Lamarck recognised this, and this is where the most famous part of Lamarckism comes in as an explanatory mechanism: the inheritance of acquired characteristics.

It must be noted, though, that the inheritance of acquired characteristics is not Lamarck’s original idea and was very widespread, although he did (unsuccessfully, as we will see) expand it with his own original additions.

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Inheritance of acquired characteristics is a fairly simple concept (at least it is if you forget all you know about modern biology, as you’re supposed to do when examining history of science). I will explain Lamarck’s version using the usual example of the giraffe.

So the giraffe is living in a savannah where the trees are growing taller. This induces a besoin (= “need“, not “want” as is usually wrongly translated) in the giraffe, and it changes its behaviour to be able to reach the taller branches. For example, it would extend its neck more. According to Lamarck, this extra use of the neck would cause the neck to grow through the flow of more vital fluid. This new neck state is an acquired characteristic, and it can be passed on to the offspring, hence why we speak of the inheritance of acquired characteristics.

The opposite is also true: if an organ is disused, then vital fluid will flow out of it and it will atrophy. This explains why cave animals have reduced eyes, for example.

Giraffe source: gmacfadyen

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Another example Lamarck used, just for your interest, is the membrane between the digits of many swimming animals, like frogs, sea turtles, otters, and beavers. By swimming more, the animal has a need to push water out of the way, and so the interdigital membrane gets used as a paddle, causing more vital fluid to flow into it.

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The key novelty in Lamarck’s concept of the inheritance of acquired characteristics was the invocation of vital fluid. The real ruckus here isn’t much any physiological discovery (vital fluid or anything close to it has never been discovered). Instead, it’s the completely naturalistic and mechanistic view that postulating something like vital fluid espouses, and it was fairly controversial at the time. One the social side, it was controversial because it does away with any need for a God guiding evolution (although, as we will see later, theologians did a complete U-turn when Darwin came into the picture!). And the concept of such a dynamic system went against the predominant view of the time that while organisms may change, they only change in preset ways – “there is an optimal phenotype for each environment. How it gets there, we don’t know, but vital fluid isn’t it” would have been the reaction of the typical naturalist of the time.

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So, to summarise, there are two foundational principles of Lamarckism. The first is the idea of a natural, linear progression along a scale of complexity. However, as the diversity of life demonstrates, there is a confounding factor leading to large meanders on the way to perfection: organisms will adapt to their local environments, leading to a diversity of forms even at the same level of complexity.

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So, now that we know what Lamarckism is all about, we can get back to the modern age and look at it critically, starting with what he got correct.

Any philosopher of science or thesis advisor will tell you that identifying the correct problems and asking the right questions is half the step towards good science. And in that respect, Lamarck excelled: he successfully figured out the four core problems of natural history of the time:

  1. Why are fossil forms different than extant ones?

  2. Why are some organisms more complex than others?

  3. Why is there so much diversity?

  4. Why are organisms well-suited to their environment?

img21But beyond that, he failed at providing any correct explanation – although it must be stressed that it was not through any fault of his own. If any of us (or Chucky) were alive at the time and working with the same material, we most probably would have converged on a similar set of ideas, and not on natural selection or mutationism.

Lamarck said that fossil forms are different because they always get replaced by the more complex ones as the lineage goes up the escalator of complexity. We now know that fossil forms are on a different part of a phylogeny and hence are different.

There is no such thing as a scale of complexity; complex traits arise in individual taxa as a result of their unique circumstances. Most typical examples of complexity, e.g. multicellularity, are unique phenomena that are in no way indicative of pervasive trends.

Diversity is not a product of constant biogenesis; all the evidence points to a single origin of life. Diversity is a result of speciation.

There is no such thing as vital fluid. Organisms are seemingly well-suited to their environment because the organisms that we see have made it through the unforgiving grinder of natural selection. It’s a perceptory illusion more than anything else, really.

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In natural selection as understood today, you consider a whole population of giraffes with variable neck sizes. Those with the taller necks will be able to reach higher tree branches and thus have access to more food. This gives them more energy and thus a slight advantage in reproduction, meaning that in the long run, they will produce more offspring. Assuming a genetic basis to neck length, this means that more offspring with taller necks are likely to be born, meaning that they will outcompete the shorter-necked ones over many generations.

In Lamarckism, the giraffe needs to reach taller trees and so its neck lengthens, and that longer neck gets passed on to the offspring.

It’s obvious to us now that this, the second core of Lamarckism, fails.

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The idea of a progression up a scale of complexity fails even on a molecular level, as the entire basis of molecular evolution shows. Motoo Kimura and Tomoko Ohta are the founders of the dominant neutral and nearly-neutral theories of molecular evolution, respectively. What they show is that mutations are overwhelmingly neutral – they have no effect on the fitness of an organism; nerly-neutral theory expands this a bit by saying that many of these neutral mutations will have an effect that is too tiny to really be noticeable. The rest of the mutations are deleterious, with only a small amount of mutations actually being beneficial.

If there was a preset linear progression to perfection, then we would expect all mutations to be advantageous, and that’s just not corroborated by any evidence.

Diagram source: Bromham L & Penny D. 2003. The modern molecular clock. Nature Reviews Genetics 4, 216-224.

The bit at the bottom of the slide snuck in because I co-opted this slide from my natural selection lecture. It’s not really relevant here, go to that post to see what it’s all about.

img25So we now know that Lamarckism is false, but it hasn’t always been this way. A full coverage of the history of Lamarckism would require a lecture/post all on its own, so this is just a broad look.

The idea of vital fluids never really took off, and thus Lamarckism – and evolution – remained contested until Darwin’s Origin of Species took the world by storm. Darwin showed the reality of evolution, but hadn’t managed to bring everyone on board with natural selection.

The idea of inherited acquired traits (IAT) which had been present (and even used by Darwin in his thoughts on social evolution) became synonymised with Lamarckism, and a whole host of neo-Lamarckisms with IAT at their core sprung up to counter natural selection. In scientific circles, these neo-Lamarckisms generally won out over natural selection. Outside of science, a curious thing happened: theology, which half a century ago was fervently opposed to Lamarckism, now endorsed it fully – only because Lamarckism, gutted of vital fluids and only retaining IATs, could easily be endowed with the action of a creative deity intelligently designing adaptations, much more comfortable than the supposed “randomness” of natural selection (these people were never that bright).

In 1900, both the neo-Lamarckists and the selectionists got beaten down by the rediscovery of genetics and the evolutionary movement that arose therefrom: mutationism. The three movements were at odds with each other. The difference betweent he three are what they stress as the dominant force in evolution: mutations (mutationism), natural selection (selectionism), IAT (neo-Lamarckism).

By 1910, the neo-Lamarckisms had started their decline, with Weismannism gaining more prominence. Weismannism is pure selectionism, what we now would term ultra-Darwinism. It generally became a two-dog race between mutationism and selectionism, which endured until the 1930s, when the Modern Synthesis began to get crafted – the Modern Synthesis, completed in the 1950s, was basically a fusion of mutationism and selectionism, with a heap of other stuff added to the mix. None of that other stuff included neo-Lamarckism, which had by then well and truly died.

At least it was so in the European and American academias. In Russia, a radically different story was unfolding, one of the dark chapters of the history of biology and of science in general: lysenkoism. Trofim Lysenko was a so-so scientist with very high political acumen. He used the latter to rise to the top of Soviet biological academia and became head of the Academy of Agricultural Sciences by the 1930s. And there, he began a dictatorship where he imposed his own idea of evolution – michurinism, rebranded neo-Lamarckism – and executed those geneticists who did not agree with this stance. Michurinism became the “new biology”, well-suited to collectivization and communism – there was a very heavy mixing of politics with the (non-existent) science, no doubt because Lysenko was Stalin’s little lap dog. The spread of Lysenkoism is also directly tied to the failure of Soviet collectivization and all the associated agricultural crises, because that’s just what you get when you base your country’s agricultural system on disproven theories. Lysenkoism went away officially in 1964, although strands of it remained for a couple of decades afterwards. Now it’s remembered as a blotch on the history of Russia and Russian science.

So, now, all Lamarckisms and neo-Lamarckisms are dead. However, the rise of epigenetics has led to a burgeoning and, in my opinion, misguided movement of neo-neo-Lamarckism (they get referred to as neo-Lamarckists, but that’s wrong, since neo-Lamarckism refers to the Lamarckisms of the 1860s-1930s). It bears little resemblance to the Lamarckism of yore, and postulates that epigenetic modifications – environmentally-induced changes to DNA and gene regulation that really require their own post – are an important driving force in evolution.

I don’t quite see their argument for the simple reason that epigenetic modifications must be made in germ cells to be passed on to the offspring (although internally-brooding organisms can also modify the environment of the womb to induce epigenetic changes in the developing fetus). So, for example, a snail that develops spines in response to predators in the water will not pass these spines on to its offspring automatically. What will get passed on is the capability to develop spines in the same situation… but this is regular heredity which doesn’t need any fancy neo-neo-Lamarckism to explain.

It’s my job, so I will keep an open mind about this – there may be cases where epigenetics does indeed play an important role in evolution. I just haven’t seen them yet. I do see epigenetics as important for ecology though, so that may be a more viable bridge for neo-neo-Lamarckists to attempt to build.

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For books on Lamarckism, I recommend these two:

Burkhardt Jr.’s 1977 The Spirit of System: Lamarck and Evolutionary Biology goes over Lamarckism, and is the best overview you can wish for.

For more on the battles between neo-Lamarckism, selectionism, and mutationism, see Bowler’s classic 1992 study in the history of evolution, The Eclipse of Darwinism: Anti-Darwinian Evolution Theories in the Decades Around 1900.

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