Lamarck and Darwin revisited

Abstract

Evolution had been puzzled scholars for centuries until Lamarck and Darwin proposed their general theories of evolution. While Lamarck was shown to be wrong, Darwin's insights revolutionized biology.

“That little word ‘why’ has run through all universe from the first day of creation, and all nature cries every minute to its creator ‘why’. And for seven thousand years it has had no answer” exclaimed Captain Lebyadkin, one of the characters of Fyodor Dostoyevsky's novel Demons. The protagonists of the Scientific Revolution of the 17^th century had an answer: the world was a machine, set in motion by a divine force and operating according to natural laws.

Isaac Newton explained in his Philosophiae Naturalis Principia Mathematica: “Blind metaphysical necessity, which is certainly the same always and everywhere, could produce no variety of things. All that diversity of natural things which we find suited to different times and places could arise from nothing but the ideas and will of a Being, necessarily existing”. For him and his followers, religious beliefs predicted a rational order beneath the apparent chaos in nature. Truth disclosed by science may have been identified with God's thoughts.

Did these members of the intellectual elite not notice the misery of the common people who were struggling to survive and feed their children? The philosopher and mathematician Gottfried Leibniz proposed a principle of pre‐established harmony to account for this apparent dichotomy: good and evil are intertwined to make this the best of all possible worlds. Many scholars of the 18^th century, the “Age of Enlightenment”, perceived the world in the same way: evil had no substantive nature. Just as darkness is the absence of light, evil means the absence of good. The enlighteners believed that once the light of knowledge penetrates the darkness of ignorance and superstition, mankind will see things as they are. Many of them may have been theists—or rather deists, who claimed that God exists as a first cause that created the universe but does no longer intervene in the world. Some may have been agnostics or atheists, but most shared the creed of the philosopher Nicolas de Condorcet that, thanks to human reason, the perfectibility of humans was unlimited.

Immanuel Kant, who extolled the enlightenment as the age of “man's leaving his self‐caused immaturity”, attempted to apply Newton's theory of gravitation to the evolution of the cosmos. He considered human reason to be powerful, but also confined since we face difficulties in understanding life: “It would be absurd for humans to hope that there may yet arise a Newton who could make comprehensible even the generation of a blade of grass according to natural laws which no intention has ordered”. Kant surmised that higher species evolve from lower ones, but could not see how lower species would develop from unorganized matter. He inferred that the idea of nature as purposively directed towards the evolution of rational beings submitted to moral laws has allowed us to conceive God as the author of nature and creator of life.

The first general theory of evolution of life was put forward by Jean Baptiste Lamarck in 1809 in his book Philosophie Zoologique. Simple organisms are spontaneously generated from inanimate matter and evolve into more complex ones. This intrinsic trend towards more complexity is reinforced by an adaptive force: the environment creates needs to which organisms respond by using features, which are then accentuated or attenuated through use and disuse. The idea is commonly illustrated by images of giraffes stretching their necks to reach leaves high in trees, which would gradually lengthen their necks. In the same way, Lamarck argued, a blacksmith, through his work, strengthens the muscles in his arms. The characteristics that an individual organism acquired through use or disuse are then passed on to its offspring. Lamarck was a practising naturalist with a broad knowledge of plants and animals but, as biologist Hans Driesch wrote, “Lamarck's theory of descend is purely fictitious construction and no proof is offered” 1. It is not surprising that he referred to God as the “sublime author of nature” in line with the deism of his scholarly contemporaries.

In the first half of the 19^th century, Alfred Russell Wallace and Charles Darwin developed the idea that natural selection might be involved in evolution. Darwin published his theory in 1959 in his book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. His conception of the world completely differs from that of classical rationalism. No rational designer was present at the beginning, and life is a struggle for scarce resources that conditions organisms’ stability, or, put differently, their onticity. Whatever increases the chance to survive is “good”, and whatever endangers it, is “bad”. Living beings that fit less into their environment, perish, the fittest ones survive and reason is gained: but this reason comes post factum, it is not present from the beginning as Newton, Kant or Lamarck surmised. Darwin presents us the Ontology of Evil.

Unlike Lamarck, Darwin and Wallace were empiricists and carefully based their arguments on observations. Lamarck did not recognize the merits of Lavoisier in developing modern chemistry and supported his material life force with obsolete concepts from alchemy, whereas Darwin painstakingly supported his arguments by data from other disciplines. But two important discoveries were not available to him in 1859. In 1867, Rudolf Clausius formulated the second law of thermodynamics, the fundamental implications of which for biology became clear only a century later. In 1866, Gregor Mendel published his theory on heredity, but biologists became aware of its importance only in 1900.

Not aware of Mendel's work, Darwin published his own theory of heredity in 1868, calling it pangenesis. He proposed that each part of the body emits small organic particles called gemmules that aggregate in the gonads to contribute heritable information to the gametes. Darwin thought that environmental effects that altered characteristics would alter gemmules, which would then be transferred to offspring. His pangenesis theory allowed for the Lamarckian idea of transmission of acquired characteristics through use and disuse.

Nowadays the term “Lamarckism” is used as an acronym for the inheritance of acquired characteristics. Accordingly, Charles Darwin himself may be classified as a Lamarckian. Yet, Darwin's theory underwent its own evolution up to the neo‐Darwinian synthesis, which denied that acquired characteristics could be inherited. Upon the triumph of Neo‐Darwinism in the 20^th century, Lamarck and his ideas were being discredited as absurd or even dangerous. Curiously, around the turn of the 21^st century, several scientists have been trying to resuscitate Lamarck's idea referring to the phenomenon of epigenetic inheritance, which has become a matter of controversy.

It concerns what John Maynard Smith called the dual inheritance system 2: the genome that transmits information vertically between generations, and an epigenetic or cellular inheritance system, that depends on gene activation, and which transmits states of differentiation horizontally during development. Cellular inheritance has been attributed mainly to methylation of the DNA, histone modifications and long‐lived noncoding RNAs, which collectively are called the “epigenome”. Occasionally, epigenetic changes are transmitted vertically during sexual reproduction, which has been called intergenerational epigenetic heredity. Some scientists think it plays a role in shaping evolution; Eva Jablonka and Marion J. Lamb titled their 1998 book Epigenetic Inheritance and Evolution. The Lamarckian Dimension. Many have expressed scepticism; Brian Hall criticized it 3 by referring to Maynard Smith's argument that environmentally induced changes tend to reduce, not enhance fitness, and that the flexibility required for epigenetic systems is at odds with the accurate replication required for genetic inheritance.

The genome represents the phylogenetic memory, which has been accumulating knowledge for millions of generations from random genetic variations. Maintaining the stability of the phylogenetic memory is a costly business: energy‐dependent repair mechanisms enable an error rate as low as 1 in 10¹⁰ base pairs, which is incredibly accurate. On the other hand, the error rate of DNA methylation, which apparently dispenses with repair correction, is as high as 10⁻¹ per site 4. We can tentatively assume that the occasional intergeneration epigenetic inheritance is contingent to this intrinsic high error rate, which would exclude evolutionary relevance of the inheritance of acquired characteristics.

Instead of the standard use of the term “Lamarckism”, we might apply it to a different part of Lamarck's theory: the idea that biological evolution is progressive in time. Darwin himself may have been equivocal in his writing about the evolutionary progress, while some prominent “Darwinists”, such as Stephen Jay Gould, were either rejecting it, or, like Julian Huxley and Richard Dawkins, observing it “nearly everywhere”. By anchoring Darwinism in the contemporary interpretation of the second law of thermodynamics, we can interpret evolution as a process of gaining and progressively accumulating knowledge. The basic thesis of this “cognitive Darwinism” stipulates that this process is not deterministic: actual knowledge knows nothing of what is hidden behind the horizon; new knowledge can only be acquired by blindly fumbling in all directions. Biological species compete for energy gradients. The losers end up in a deadlock, and new and more complex living forms, accumulating knowledge in a ratchet‐like manner, move ahead in the evolutionary maze 5.

Darwin's discovery has been the revolutionary breakthrough. The year 1859 divides the history of human thought into two ages: before and after Darwin.

EMBO Reports (2019) 20: e47922