We have heard quite a lot in recent times about a resurgence of “Lamarckian” mechanisms, based largely on findings involving epigenetics. In this case, environmental differences cause changes in the patterns of expression of genes, and these alterations can sometimes be passed on through at least a few generations.
There are two reasons why it is inaccurate to consider this kind of change in heritable characteristics induced by the environment as “Lamarckian inheritance”.
One, Lamarck did not think that the environment imposed direct effects on organisms that were then passed on. He argued that the environment created needs to which organisms responded by using some features more and others less, that this resulted in those features being accentuated or attenuated, and that this difference was then inherited by offspring. As he wrote,
It is now necessary to explain what I mean by this statement: The environment affects the shape and organization of animals, that is to say that when the environment becomes very different, it produces in the course of time corresponding modifications in the shape and organization of animals. It is true, if this statement were to be taken literally, I should be convicted of an error; for, whatever the environment may do, it does not work any direct modification whatever in the shape and organization of animals. [Translated as in Kampourakis and Zogza (2007)]
What people insist on dubbing “Lamarckian inheritance” in the context of epigenetics is actually closer to the view held by Darwin than by Lamarck. In the second part of his 1858 joint paper with Wallace (excerpted from an 1857 letter to Asa Gray), Darwin wrote,
Selection acts only by the accumulation of slight or greater variations, caused by external conditions, or by the mere fact that in generation the child is not absolutely similar to its parent.
…
Now take the case of a country undergoing some change. This will tend to cause some of its inhabitants to vary slightly—not but that I believe most beings vary at all times enough for selection to act on them. Some of its inhabitants will be exterminated; and the remainder will be exposed to the mutual action of a different set of inhabitants, which I believe to be far more important to the life of each being than mere climate.
We can read similar things in the Origin:
I have hitherto sometimes spoken as if the variations—so common and multiform in organic beings under domestication, and in a lesser degree in those in a state of nature—had been due to chance. This, of course, is a wholly incorrect expression, but it serves to acknowledge plainly our ignorance of the cause of each particular variation. Some authors believe it to be as much the function of the reproductive system to produce individual differences, or very slight deviations of structure, as to make the child like its parents. But the much greater variability, as well as the greater frequency of monstrosities, under domestication or cultivation, than under nature, leads me to believe that deviations of structure are in some way due to the nature of the conditions of life, to which the parents and their more remote ancestors have been exposed during several generations. I have remarked in the first chapter—but a long catalogue of facts which cannot be here given would be necessary to show the truth of the remark—that the reproductive system is eminently susceptible to changes in the conditions of life; and to this system being functionally disturbed in the parents, I chiefly attribute the varying or plastic condition of the offspring. The male and female sexual elements seem to be affected before that union takes place which is to form a new being. In the case of “sporting” plants, the bud, which in its earliest condition does not apparently differ essentially from an ovule, is alone affected. But why, because the reproductive system is disturbed, this or that part should vary more or less, we are profoundly ignorant. Nevertheless, we can here and there dimly catch a faint ray of light, and we may feel sure that there must be some cause for each deviation of structure, however slight.
Two, the idea of inheritance of acquired characteristics predates Lamarck, was the dominant view in his time, and remained common long afterward. As Morse (1903) wrote,
Jean Lamarck first used the term “acquired character” to designate characters such as these and to him are are we to look for the first clear statement of the case. By this it is not to be understood that the idea of the transmission of acquired characters arose with Lamarck. No great generalization ever arose or ever can arise with one man alone. The attribution of the idea of the transmission of acquired characters to Lamarck falls in the same category as attributing evolution to Darwin.
Zirkle (1946) was more forceful yet,
What Lamarck really did was to accept the hypothesis that acquired characters were heritable, a notion which had been held almost universally for well over two thousand years and which his contemporaries accepted as a matter of course, and to assume that the results of such inheritance were cumulative from generation to generation, thus producing, in time, new species. His individual contribution to biological theory consisted in his application to the problem of the origin of species of the view that acquired characters were inherited and in showing that evolution could be inferred logically from the accepted biological hypotheses. He would doubtless have been greatly astonished to learn that a belief in the inheritance of acquired characters is now labeled “Lamarckian,” although he would almost certainly have felt flattered if evolution itself had been so designated.
Darwin, like Lamarck, invoked use and disuse and inheritance of acquired changes1; the Origin includes an entire section on it, the first part of which reads,
Effects of Use and Disuse.—From the facts alluded to in the first chapter, I think there can be little doubt that use in our domestic animals strengthens and enlarges certain parts, and disuse diminishes them; and that such modifications are inherited. Under free nature, we can have no standard of comparison, by which to judge of the effects of long-continued use or disuse, for we know not the parent-forms; but many animals have structures which can be explained by the effects of disuse. As Professor Owen has remarked, there is no greater anomaly in nature than a bird that cannot fly; yet there are several in this state. The logger-headed duck of South America can only flap along the surface of the water, and has its wings in nearly the same condition as the domestic Aylesbury duck. As the larger ground-feeding birds seldom take flight except to escape danger, I believe that the nearly wingless condition of several birds, which now inhabit or have lately inhabited several oceanic islands, tenanted by no beast of prey, has been caused by disuse. The ostrich indeed inhabits continents and is exposed to danger from which it cannot escape by flight, but by kicking it can defend itself from enemies, as well as any of the smaller quadrupeds. We may imagine that the early progenitor of the ostrich had habits like those of a bustard, and that as natural selection increased in successive generations the size and weight of its body, its legs were used more, and its wings less, until they became incapable of flight.
As was argued by Parkyn (1911),
It is difficult to understand how anyone well acquainted with Darwin’s works can come to any other conclusion than that he firmly believed in Lamarck’s principle of the transmission of characters acquired by use.
Designating epigenetics as Lamarckian greatly misconstrues what Lamarck actually argued. The parts of Lamarckian theory to which it does refer were likewise part of early Darwinian theory. In short, there is no vindication of Lamarck’s mechanism to be granted by epigenetics. That said, there is no doubt that Lamarck’s contributions to evolutionary thinking should be better appreciated. Certainly, the first step toward this would be an effort to understand what he actually proposed.
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Updated notes:
1) See the comments discussion. Wilkins has pointed out that Darwin was not simply a “Lamarckian” in terms of new traits arising through need+use/disuse (rather, he suggested that the strength of inheritability of traits is affected by use). However, Darwin did invoke disuse as a reason that traits could be lost which is enough to show that he did not throw out use and disuse as a mechanism of trait change.
