Lamarck and Darwin: two divergent visions of the living world

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The last two decades have seen an accumulation of scientific data on so-called epigenetic phenomena, changes in the expression of genes induced by the environment and transmitted temporarily to the offspring. This has led some authors to make the connection with Lamarckism, some even go so far as to propose the elaboration of a new synthetic theory of evolution combining the theories of Lamarck and Darwin. A comparison of the basic principles of these two theories shows that their visions of the living world are too divergent to be reconcilable. This does not detract from the fact that research on epigenetic phenomena will certainly lead to an enrichment of Darwinian theory.

1. Conflicts and confusion between Lamarckism and Darwinism

lamarck - philosophie - zoologique - evolution - encyclopedie environnement
Figure 1. Portrait of Jean-Baptiste Lamarck (by Charles Thévenin) and cover page of his book “Philosophie zoologique, ou Exposition des considérations relatives à l’histoire naturelle des animaux… ” published in 1809 [Source: portrait – Charles Thévenin [Public domain], via Wikimedia Commons. Cover page: CC BY 4.0, via Wikimedia Commons]
The first coherent and solidly supported theory on the evolution of life was established in 1800 by Jean-Baptiste Lamarck (1744-1829), a great French naturalist, and published in 1809 in his book Philosophie zoologique (Figure 1).

Fifty years later, in England, The Origin of Species was published in which Charles Darwin (1809-1882) developed his own theory on the transformation of species by “descent with modification” (Figure 2) (see focus Darwin).

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Figure 2. Portrait of Charles Darwin (by John Collier, 1883) and cover page of his book “The origin of species by mean of natural selection, on the…”, 1859 edition [Source: portrait – John Collier [Public domain], via Wikimedia Commons. Cover page: public domain]
The great common point between the theories of these two great naturalists is the affirmation of the evolutionary fact, which goes against creationism, universally accepted until then. But their conceptions of the living world diverge radically on such essential issues as the origin of life and the very mechanisms of evolution. Genetics, born at the very beginning of the 20th century, provided Darwin theory with knowledge that was sorely lacking. In the 1940s, it made it possible to develop the synthetic theory of evolution or neodarwinism. One might have thought that the debate between Lamarkism and Darwinism was over.

This is not the case, these two theories are still the subject of conflicts and confusion. For the general public, evolution – when it is accepted, which is far from always being the case [1] – is generally understood in a Lamarckian way. That is, evolutionary changes occur under the more or less direct influence of the environment. The Darwinian process, which implies that fortuitous genetic variations may be the basis for significant biological transformations (see below), strikes common sense.

Surprisingly enough, these conflicts and confusions are also found among biologists, philosophers and science historians. Conflicts that are often linked to a deep rejection of Darwinism, for non-scientific motivations (seeTheory of Evolution: misunderstandings and resistance). Confusions that are due to misunderstandings or difficulties of interpretation. This is particularly the case with some of Lamarck’s writings on the appearance of life, which are ambiguous, if not contradictory [2].

This situation has been accentuated over the past two decades with the importance acquired by the epigenetic imprints of the genome, which is discussed in several articles in this encyclopedia (see Adaptation: Responding to environmental challenges; Epigenetics, the genome and its environment; The adaptation of organisms to their environment). Very briefly, these imprints involve chemical changes in DNA (or the proteins surrounding it), but do not change the sequence of nucleobases (so they are not mutations) and are reversible. They are usually triggered by stressful situations and influence gene expression, often in an adaptive sense. They can be transmitted to offspring for a few generations, referred to as epigenetic memory or transgenerational effect. This type of phenomenon, known for a long time, has been the subject of renewed studies since the beginning of the century (see Epigenetics, the genome and its environment).

This transgenerational effect, although transitory, may recall the heredity of the acquired traits discussed later. A phenomenon that is often, and wrongly, considered to be the main characteristic of Lamarck’s theory. This has led biologists to re-launch the debate on a possible update of this one. Some even go so far as to mention the need for a synthesis between the two theories. We will see that the considerable differences between them do not argue in favour of such an idea.

This subject will be treated here from the strict biological point of view, by comparing the basic principles of these theories and the visions of the living world that flow from them, particularly on the origin of life and on the mechanisms of transformation of species. An article by Laurent Loison and Francesca Merlin, which addresses this problem from the perspective of the history and philosophy of science, can also be found in the Encyclopaedia Universalis [3].

2. The origin of living beings and their genealogical relationship

In Lamarck’s vision, the “simplest” or “most imperfect” organisms always appear as “spontaneous generation” or “direct generation”. He writes in Zoological Philosophy: “In its march, nature began, and continues to do so every day [underlined by the author of this article] by forming the simplest organized bodies and it only forms directly those, that is to say, these first drafts of the organization, which have been designated by the expression of spontaneous generations“.

It should be noted in passing that in the light of our current knowledge on the extraordinary complexity of the most elementary living cells and on the origin of life, this idea of permanent spontaneous generation makes people smile. As well as the qualifier “simple” for living organisms (Read the articles The Origin of Life as seen by a geologist who loves astronomy; Once upon a time there was life… and Origin of the first cells: the engineer’s point of view).

Lamarck imagines that these primitive organisms gradually become more complex over the course of geological time to reach all existing living beings. A complexity that is synonymous for him with perfection and which would result from an inherent property of the living beings to which we will return later.

Figure 3. Representation of phylogeny of animal species according to Lamarck. On the left, diagram from his book “Philosophie zoologique” (1809) showing the increasing complexity of species. On the right, representation of the evolution of living organisms over time. Appeared by spontaneous generation, organisms become more complex over time. There is no filiation between two distinct lines. [Source: excerpt from the book (Public Domain); Diagram: JC Bregliano]
Thus, for Lamarck, spontaneous generations would occur frequently and, each time, the process of complexification would be repeated (although on these two points his writings are somewhat ambiguous). Thus, since the origin of the planet, the simplest organisms would spontaneously appear from the inert matter and would repeatedly initiate series that would evolve in parallel (Figure 3). Within each of these lines, filiation exists, from the simplest to the most complex, but there can be no genealogical relationship between the lines.

Lamarck also postulates that primitive plants and animals appear in two independent ways. It also allowed two separate routes for animals. One is relatively short, starting with what were then called “infusoria” (unicellular microorganisms) and the other is longer, starting with the simplest worms and leading to the vertebrates (Figure 3). In short, in Lamarckian theory, the living world would be composed of multiple successive and independent lines. There would be no single common ancestor.

Darwin, for his part, does not speak of the appearance of life in The Origin of Species, except to say that the knowledge of his time did not allow him to approach it. It is sometimes mentioned in his correspondence, notably in a letter from 1871 to his best friend Joseph Hooker. “It is often said that all the conditions for the first production of a living organism are present, which could ever have been present. But if (and oh! what a big if!) we could conceive in some warm little pond, with all sorts of ammonia and phosphoric salts, light, heat, electricity, etcetera present, that a protein compound was chemically formed, ready to undergo still more complex changes, at the present day such matter would be instantly devoured or absorbed, which would not have been the case before living creatures were formed.“.

darwin - schema - evolution - especes - the origin of species darwin
Figure 4. On the left, a diagram in which Darwin describes the principle of “descent with modification”. This is the only scheme that has been published in “The Origin of Species”. On the right, a sketch of a phylogenetic tree by Darwin, diagram taken from the 1st notebook (known as the B notebook) on the “Transmutation of Species” (1837-1838). Darwin describes very clearly here his ideas on the appearance and extinction of species. [Source: Public domain]
So for Darwin, the appearance of life could only have occurred in a world that was still abiotic, through a very slow process. He refuses the idea of permanent spontaneous generation, which has been universally accepted since Pasteur [4]. As a result, all living beings on the planet are derived from this ancestral form of life (Figure 4). In the conclusion of The Origin of Species he writes:”…all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed. “.

phylogenie - especes - schema - ancêtre - LUCA - Last Universal Common Ancestor - phylogeny of species
Figure 5. Schema summarizing the phylogeny of species from a common ancestor called LUCA (Last Universal Common Ancestor) [Source: Public domain].
This vision is fully in line with modern scientific research that is trying to understand the characteristics of this primordial ancestral form, called LUCA for Last Universal Common Ancestor (Figure 5). On this subject, we can consult the videos of the remarkable symposium “The Origins of Life” organized in 2013 by the french Academy of Sciences [5].

We can therefore see that from the outset, on the very origin of life, Lamarck and Darwin’s theories are based on two very different visions of the structure of the living world.

There are at least two other important differences between these theories. As they both concern the modalities of evolution, they are very intertwined; but for the sake of clarity we will present them separately.

3. The mechanisms of evolutionary transformations

We are entering into what is really the heart of the two theories. According to Lamarck, the variations of the individuals who are at the root of the transformation of species occur under the effect of external circumstances leading to “needs”, themselves at the origin of “actions” or “efforts”, which will create “habits”. Let us quote him: “The second conclusion is my own: it assumes that, by the influence of circumstances on habits, and then by the influence of habits on the condition of the parts of the animal, and even on that of the organization, each animal can receive in its parts and its organization, changes that can become very significant. ».

In the same Chapter VII of Zoological Philosophy it states a first law: “In any animal which has not gone beyond the end of its development, the more frequent and sustained use of any organ gradually strengthens, develops, enlarges (…) this organ; while the constant defect of such an organ, imperceptibly weakens and deteriorates it, gradually reduces its faculties and eventually makes it disappear“.

In plants, Lamarck is led to propose an even more direct influence of the environment on the organism because, of course, we cannot talk about efforts and habits in plants! In his theory, variations are therefore always induced, more or less directly, under the influence of external conditions.

Since the discovery of genetic mutations at the beginning of the 20th century, neolamarckians have had to integrate the idea that these mutations are at the root of variations. They then imagined that they had to be directed by the environment, on specific genes, to adapt the organism to its environment. But this idea is in contradiction with all the experimental research carried out since the 1940s. The most recent and one of the most demonstrative was published in 1997 by an American team [6]. We will come back to this later.

Based on these induced variations, the transformation of species would be driven by a trend towards increasing complexity, at least in animals. This trend would have the role of “driving” in the evolution. But where would this trend come from? It would be an immanent property of living beings that irreversibly pushes them towards ever greater complexity. It is therefore a law of nature that requires no explanation. It should be noted in passing that, in the same logic, Lamarck did not believe in the extinctions of species, except those destroyed by human actions. For him, species are transformed by becoming more complex but do not become extinct.

Lamarck, however, wanted to be very materialistic and often repeats that the living obey only physical laws. It can be admitted that the reference to the “Supreme Author of all things”, frequent in his writings, is a matter of political opportunism (Napoleon did not appreciate that the role of God was neglected!). Nevertheless, this push towards complexity, which according to him is the exclusive property of the living world, is a singular reminder of vitalismPhilosophical doctrine which establishes the existence of a vital principle distinct from both the thinking soul and the physico-chemical properties of the body, governing the phenomena of life (André Lalande’s definition)..

It should be noted that this trend towards complexity, as well as the influence of the environment on changes, both function as an anti-hasard. The share of randomness in the transformation of species is therefore limited in Lamarck. This is what seduces many people in his theory, including biologists and philosophers of science.

Darwin, for his part, strongly contests that external conditions are the cause of the variations. In the introduction to The Origin of Species, he writes: “Naturalists continually refer to external conditions, such as climate, food, etc., as the only possible cause of variation. In one very limited sense, as we shall hereafter see, this may be true; but it is preposterous to attribute to mere external conditions, the structure, for instance, of the woodpecker, with its feet, tail, beak, and tongue, so admirably adapted to catch insects under the bark of trees. ... ». He also refuses the idea of a force pushing for increasing complexity, which he finds “silly”.

In Darwinian theory, the main forces at play are “spontaneous and accidentalhereditary variations from which natural selection operates (see Figure 4; see Theory of Evolution: Misunderstandings and Resistance). It is the latter that plays the role of “engine” of evolution, accidental variations are only the basic “material”. Darwin writes: “I am convinced that Natural Selection has been the main but not exclusive means of modification“.

darwin - lamarck - evolution - espece - girafe - schema - transformation evolutive - selection naturelle - evolution species darwin
Figure 6. Diagram summarizing the evolutionary transformation of species according to Lamarck (A) and Darwin (B). In Lamarck (A1 to A3), this transformation occurs under the effect of external circumstances leading to “needs”: here, the giraffe’s neck will lengthen (arrows) so that it can feed on the high leaves of the trees. For Darwin, “spontaneous and accidental” hereditary variations within a species will increase its diversity (B1) and this is what natural selection is based on: in the example of the giraffe, there are neck size variations in an ancestor of the giraffe and the environment (the height of the branches) will serve as a selection screen; long-necked individuals will reproduce more effectively because they are better fed (B2). Diagram based on Solarist’s drawing (Own work) [CC BY 3.0], via Wikimedia Commons. [Source: Photo © Jacques Joyard]
The Darwinian evolutionary process therefore does not imply any finality. The combination of accidental variation and selection results in the best adaptation of a population at a given time in a given environment, with a significant proportion of hazards (see Focus The ups and downs of evolution: the role of small numbers). By itself, this process does not imply any tendency towards complexity, let alone perfection. There may be acquisition of new functions but also loss of functions, thus simplification, which is often observed in parasites. Not to mention the extinctions of species, or even entire zoological groups, , not accepted by Lamarck. Darwinian evolutionists readily say that if evolution were to begin again, there is no reason to believe that it would follow the same path. Here again, there is a wide gap between the Lamarckian and Darwinian visions.

4. Transmission of changes to progeny

Let us return to the question already mentioned of the inheritance of acquired characteristics, an expression often associated with Lamarck, but which is in fact much later. This third point is much less different between the two theories than the previous ones, but still important with regard to the knowledge accumulated in genetics.

Under the pen of biologists or science historians, this inheritance of acquired characteristics is sometimes presented as an analogy between Lamarck and Darwin’s theories and sometimes as the only major difference between them. It is therefore difficult for non-specialists to find their way around. Let’s try to clarify.

First of all, let us recall that in both Lamarck’s and Darwin’s time, we knew nothing about the mechanisms of heredity [7]. So we had to try to understand why dogs don’t make cats…, among other things!

Since, in Lamarckism, variations occur under the influence of the environment, they are not, from the outset, hereditary (today we say: they are not genetic, but only phenotypic). However, for them to play a role in the transformation of species, they must absolutely be heritable, hence Lamarck’s second law: “Everything that nature has caused to be lost or acquired through the influence of circumstances in which their race has long been exposed (…) it retains by generation to new individuals from them, provided that the changes acquired are common to both sexes or to those who produced these new individuals“.

Thus the characters acquired under the influence of the environment would be transmitted to the progeny. This was not a hypothesis specific to Lamarck, he took up an idea considered in his time, and already since antiquity, as self-evident, but contradicted by the research carried out over the last century.

Darwin does not totally exclude that certain traits acquired under the direct influence of the environment may become heritable. He had even brought to light a very old hypothesis (the pangenesisHypothesis inspired by very old ideas and proposed by Darwin to explain heredity, but also reproduction and development. Very small particles (gemmules) would be produced by the different parts of the body and transmitted to the reproductive organs. Darwin himself considered it to be very speculative and provisional.), dating from Hippocrates (460-370 BC), to explain heredity in general and who could also explain this heredity of the acquired characters. But for him it could only be, at best, a secondary mechanism. Concerning pangenesis, he himself wrote that this hypothesis was very speculative and provisional. He considered that the only significant variations for the transformation of species are those that are heritable, those that are now called “genetic” (see The genome between stability and variability). He wrote, from the first chapter of The Origin of Species: “Any variation which is not inherited is unimportant for us“. A phrase that can be used by breeders and agronomists who create new breeds and varieties.

In short, the inheritance of acquired characteristics is absolutely necessary to Lamarck’s theory. From Darwinian perspective, it is not an integral part of the theory, although Darwin does not exclude it completely in some cases.

5. The multiple resistances to Darwinism

This brief overview of the essential differences between the two theories shows that they are based on visions of the living world that are difficult to reconcile (see Table). To speak of a new synthesis between Darwinism and Lamarckism based on epigenetic phenomena is therefore irrelevant and can only be a source of confusion. Nevertheless, these phenomena will certainly lead to the enrichment of synthetic theory, as discussed in another article on this site (see The adaptation of organisms to their environment), but it is still too early to say more.

Table. Some major differences between Lamarck’s and Darwin’s ideas

But here we need to broaden the debate on this propensity to challenge the basic mechanisms of Darwinian theory. It is nothing new, it is a recurrent phenomenon since the publication of The Origin of Species in 1859, relaunched after the development of synthetic theory in the 1940s. As soon as new experimental facts seem to disagree with this theory, journalists, but also scientists, seize the opportunity to question it, even when the authors of these works recognize themselves in the Darwinian current.

Two recent examples are very emblematic of this trend. The first concerns the work of a Japanese researcher, Motoo Kimura, published from 1968 onwards. He published a summary of his work in 1983 in a book entitled The neutral theory of molecular evolution, which was published in 1990 [8]. In short, Kimura emphasizes that many of the DNA mutations revealed by biochemical techniques must be neutral with regards to natural selection. At the time, journalists and biologists (who had obviously not read his texts) used it against neodarwinism on the theme: “all mutations are neutral so natural selection plays no role in evolution”. It was the central pillar of Darwinian theory that was targeted.

Kimura issued very strong denials because he never wrote that all mutations were neutral. His work is not at all outside Darwinian theory; a whole chapter of his book is devoted to natural selection. Its conclusions are now widely accepted by evolutionists and population geneticists (see Genetic Polymorphism and Selection).

The second example is more recent and even more edifying. It is based on the 1987 experiments on the colibacillus carried out by a famous American geneticist, John Cairns. He used a strain carrying a defective gene responsible for a nutritional sugar deficiency, a deficiency that prevents bacteria from reproducing but does not kill them. He observes that the rate of reverse mutations (gene that has become functional again) is much higher under deficiency conditions than under normal conditions. It was then legitimate to wonder whether this abnormal rate of reversion would not be due to mutations directed by the medium, targeted precisely on the defective gene to make it functional again. Many laboratories have tackled the problem and a high-level scientific controversy has been ongoing for 10 years.

It was decided in 1997 by the remarkable experiences of Susan M. Rosenberg’s team, already mentioned above [6]. This team demonstrated that the rapidity of onset of reverse mutations was due to the induction, by the deficiency situation, of an unusually high mutagenesis rate; but it operated throughout the genome, without any targeting of the defective gene. A result that is in line with neodarwinism. This increase in the mutation rate, triggered by stress conditions, is also discussed in another article on this site, about the “SOS response” (see The genome between stability and variability).

What is particularly significant is that during the first years of the controversy, articles of extreme virulence against neodarwinism, described among other things as “an absurd theory from which we would finally be rid“, were published in specialized scientific journals, which were considered serious.

We will note that the attacks provoked by these two types of work go to the very heart of the differences between Darwinism and Lamarckism: natural selection in the first case and the random nature of mutations in the second. It is difficult not to see in it a desire to return to Lamarckism. Some of the reactions to epigenetics may well be in the same vein.

Elements of explanation on this persistent craze for the Lamarckian vision have been mentioned in another article already mentioned (see Theory of Evolution: Misunderstandings and Resistance). On the one hand, Lamarck’s role in adaptation through effort is more in line with common sense and social morality, and therefore easier to accept. As for the immanent tendency towards the living to become ever more complex, it may suggest a certain spiritualism (reinforced by Lamarck’s frequent reference to “the Supreme Author of all things“), which may reassure those who are unhappy with Darwinian materialism. Feelings rarely go hand in hand with science.

 


References and notes

Cover image. A tropical forest with monkeys and snakes (Henri Rousseau, 1910). [National Gallery of Art, Washington, USA, Public Domain]

[1] “Les Pieds dans le plat” website; http://www.lespiedsdansleplat.me/la-montee-en-puissance-des-ideologies-creationnistes/

[2] Pietro Corsi, Jean Gayon, Gabriel Gohau & Stéphane Tirard (2006) Lamarck, philosopher of nature, Ed. PUF

[3] Laurent Loison & Francesca Merlin, “Épigénétique et Théorie de l’Évolution”, Encyclopædia Universalis [online], accessed 22 September 2017. URL: http://www.universalis.fr/encyclopedie/epigenetique-et-theorie-de-l-evolution/

[4] Spontaneous generation is an Aristotelian notion that implies the appearance of living beings from inanimate matter, without ascendants. This idea was long part of common sense: it was believed that maggots were born from rotten meat. Challenged by scientists as early as the 17th century, it was not until the 19th century (when it also took the name “heterogeny”) that it was abandoned. On April 7, 1864, at a public conference in the “Grand amphitheatre” of the Sorbonne, Louis Pasteur presented the result of 6 years of research on the subject and refuted the spontaneous generation. The french Academy of Sciences will then officially declare that spontaneous generation does not exist.

[5] Website of the french Academy of Sciences; http://www.academie-sciences.fr/archivage_site/video/v160913.htm

[6] Torkelson J. et al (1997) Genome-wide hypermutation in a subpopulation of stationary-phase cells underlies recombination-dependent adaptive mutation. EMBO J. 16(11):3303-11.

[7] The work of the Czech monk and botanist Gregor Mendel (1822-1884), who first experimentally established the laws governing biological heredity, is contemporary with Darwin. However, the publication of Mendel’s work in 1866 went unnoticed at the time. It was only 35 years later, at the beginning of the 20th century, that the Dutchman Hugo de Vries, the German Carl Erich Correns and the Austrian Erich von Tschermak independently rediscovered the laws of heredity, and recognized in Mendel their discoverer. Before Mendel, genetics was much less advanced than physics was before Newton.

[8] Motoo Kimura (1990), Théorie neutraliste de l’évolution, Paris, Flammarion, (ISBN 2-082-11153-9).


The Encyclopedia of the Environment by the Association des Encyclopédies de l'Environnement et de l'Énergie (www.a3e.fr), contractually linked to the University of Grenoble Alpes and Grenoble INP, and sponsored by the French Academy of Sciences.

To cite this article: BREGLIANO Jean-Claude (May 27, 2019), Lamarck and Darwin: two divergent visions of the living world, Encyclopedia of the Environment, Accessed December 9, 2024 [online ISSN 2555-0950] url : https://www.encyclopedie-environnement.org/en/life/lamarck-and-darwin-two-divergent-visions-of-living-world/.

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拉马克和达尔文:两种对待生命世界的不同看法

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foret tropicale singes serpent - henri rousseau - lamarck - darwin - evolution - encyclopedie environnement

  在过去的二十年中,关于所谓的表观遗传现象,即环境诱导基因表达发生变化,并暂时传递给后代,这方面已经积累较多的科学数据。这导致一些作者将其与拉马克主义相关联,有些人甚至提出了将拉马克和达尔文的理论结合起来,用以阐述一种新的综合进化论。学者们通过对这两种理论的基本原理进行比较,发现二者对生命世界的看法存在巨大的分歧,且无法调和。但是,表观遗传现象的深入研究势必会丰富达尔文理论。

1.拉马克与达尔文的冲突与困惑

环境百科全书-生命-让-巴蒂斯特·拉马克
图1. 让-巴蒂斯特·拉马克(Jean-Baptiste Lamarck)的肖像(查尔斯·塞韦宁Charles Thévenin所画)和他出版于1809年的著作《动物学哲学,或与动物自然史有关的考虑的阐述……》封面[资料来源:肖像-查尔斯·塞韦宁(Charles Thévenin)[公有领域],通过维基媒体共享, 封面:知识共享许可协议BY 4.0,通过维基媒体共享]

  1800年,法国伟大的博物学家让-巴蒂斯特·拉马克(Jean-Baptiste Lamarck,1744-1829)提出了第一个连贯且得到有力支持的生命进化理论,并于1809年在他的著作《动物学哲学》中发表(图1)。

  五十年后,查尔斯·达尔文(Charles Darwin,1809-1882)在英国出版了《物种起源》一书,在其中阐述了他的关于生物通过“后代渐变”(图2)(见焦点文章达尔文)进行物种转化的理论。

环境百科全书-生命-查尔斯·达尔文
图2.查尔斯·达尔文肖像(Charles Darwin)(出自约翰·科利尔John Collier,1883年)和他的著作《物种的起源是通过自然选择,在…》1859年版的封面[来源:肖像-约翰·科利尔(John Collier)[公有领域], 通过维基共享资源。封面:公有领域]

  这两位伟大的博物学家的理论之间的最大共同点是都肯定了进化这一事实的存在,这与当时普遍接受的创世论相悖。但他们对生命世界中生命起源和进化机制等基本问题上存在根本分歧。诞生于20世纪初的遗传学能够为达尔文理论提供的知识非常有限。在20世纪40年代,遗传学的发展使现代综合进化论或新达尔文主义的产生成为可能。此时,或许人们会认为,拉马克主义和达尔文主义之争已经结束。

  然而,事实并非如此,两种理论至今仍然存在冲突和困惑。对于公众来说,进化论通常以拉马克的方式来理解,但并非所有人都能够接受它[1]。拉马克认为,进化或多或少是在环境的直接影响下发生的。达尔文的理论则强调,偶然发生的遗传变异可能是重要生物转化的基础(见下文),这是常识。

  令人惊讶的是,生物学家、哲学家和科学史学家之间也存在着这些冲突和困惑。这些冲突通常与对达尔文主义的反感相关,其动机不具有科学性(参见进化论:误解和抵抗)。困惑是由误解或解释困难引起的。拉马克关于生命诞生的一些著作尤其如此,其内容即使不是矛盾的,也有些模棱两可[2]

  在过去的20年里,随着基因组的表观遗传印记愈发重要,这种情况变得更加突出,本百科全书的几篇文章对其进行了讨论(参见适应:应对环境挑战表观遗传学,基因组及其环境生物体对环境的适应)。简而言之,这些印记涉及DNA(或其周围的蛋白质)的化学变化,但不会改变核碱基的序列(因此它们不是基因突变)并且是可逆的。在适应性意义上,它们通常由压力情况触发并影响基因表达。它们可以遗传给后代几代,称为表观遗传记忆跨代效应。这类现象早已为人所知,自本世纪初以来一直是新的科研热点(参见表观遗传学、基因组及其环境)。

  这种跨代效应虽然是短暂的,但可能会让人联想到后文所讨论的后天特征的遗传。这种现象经常被错误地认为是拉马克理论的主要特征。这导致生物学家重新发起了关于是否可能更新这一理论的讨论。有些人甚至提出了综合两种进化论以形成一种新理论的想法。但显然二者之间存在的巨大差异并不支持这种想法的实施。

  我们在这里将严格从生物学角度讨论这个主题,通过比较这些理论的基本原理和由此产生的看待生命世界的观点,特别是关于生命起源和物种转化机制的观点。劳伦特·洛伊森(Laurent Loison)和弗朗西丝卡·梅林(Francesca Merlin)的文章从科学史和科学哲学的角度解决了这个问题,二人的文章也可以在百科全书[3]中找到。

2.生物的起源及其谱系关系

  在拉马克看来,“最简单”或“最不完美”的有机体总是以“自然发生”或“直接生成”的形式出现。他在《动物学哲学》中写道:“大自然在其前进的道路上,从形成最简单的组织体开始,并且这一过程每时每刻都在发生[本文作者划线标注],也就是说,它只是直接形成了那些最早最简单的生物,这些生命形式已由自发世代的表达指定”。

  顺便提一下,出于我们目前对活细胞的异常复杂性和生命起源最基本的了解,这种永久自发产生的想法令人感到可笑。以及生命有机体的修饰语“简单”(阅读文章热爱天文学的地质学家所见的生命起源生命出现的时代:40亿年前地球海洋的化学第一个细胞的起源:工程师的观点)。

  拉马克猜想这些原始生物随着地质时间的推移而逐渐变得复杂,最终演变为所有现有生物。拉马克认为,生物的复杂性与生物自身所具有的趋于完美的特性密切相关,它是生物的固有属性,我们在后文会介绍这个属性。

环境百科全书-生命-拉马克进化论对动物物种系统发育的解读
图3.拉马克进化论对动物物种系统发育的解读。
左边是他的著作《动物学哲学》(1809)中的图表,显示了物种日益复杂的情况。右侧,表示生物体随时间的进化。由于自然发生,生物随着时间的推移变得更加复杂。两条不同的线之间没有亲缘关系。[来源:摘自本书(公有领域);图:JC布雷利亚诺(JC Bregliano)](Phenotype 表型;Time 时间;Distinct lines without any genealogical relationship没有任何谱系关系的线条;Complexification of species over time物种随时间的复杂化;New species formed by spontaneous generation自然发声形成的新物种)

  因此,对于拉马克而言,自发的演化会经常发生,并且每次复杂化的过程都是会重复的(尽管在这两点上他的著作表述有些模棱两可)。因此,自地球起源以来,最简单的生物会自发地从惰性物质中出现,并会反复启动平行进化的序列(图3)。这在每一行中,都存在亲子关系,从最简单到最复杂,但这些线之间不能有宗谱关系

  拉马克还假设原始动植物以两种独立的方式出现。并且认为动物的出现有两条不同的路径。一个相对较短,从当时所谓的“纤毛虫”(单细胞微生物)开始,另一个较长,从最简单的蠕虫开始,一直延伸到脊椎动物(图3)。简而言之,在拉马克理论中,生命世界的谱系图将由多个连续且独立的线组成。不会有一个共同的祖先。

  达尔文在《物种起源》中没有谈到生命如何在地球上出现,他所生活的那个时代的现有知识限制了他对生命的出现进行解读的可能性。但有时在他会在与友人的通信中提到自己的观点,特别是在1871年在给他最好的朋友约瑟夫·胡克的一封信中说:“人们常说,孕育生命所需的所有条件都已经存在,这些在当时可能确实已经存在。但是如果(哦!多么大胆的假设!)我们的生命可以在某个温暖的小池塘里孕育,有各种氨和磷酸盐,以及光、热、电等条件存在,产生的蛋白质等化合物有条件通过化学方式形成,并准备进行更复杂的变化,在今天,这种物质会立即被吞噬或吸收,这在生物形成之前是不可能的。”

环境百科全书-生命-带有饰变的传衍
图4.左图,达尔文描述了“带有饰变的传衍”的原理。这是在《物种起源》中发表的唯一一种假设方案。右边是达尔文的系统发育树草图,图表取自“种变说”(1837-1838)的第一个笔记本(称为B笔记本)。达尔文在这里清楚地描述了他关于物种起源和灭绝的想法。[来源:公有领域]

  所以对达尔文来说,生命的出现只能发生在一个仍然是非生物的世界中,其过程非常缓慢。他拒绝永久自然发生的想法,这是自巴斯德[4] 以来被普遍接受的想法。因此,地球上的所有生物都源自这种共同祖先的生命形式(图4)。在《物种起源》的结尾,他写道:“……所有曾经生活在这个地球上的有机生物都是从某种原始形式发展来的,这种原始的方式带来了最早的生命。”

环境百科全书-生命-物种系统发育的模式
图5.总结来自称为LUCA(最后共同祖先)的共同祖先的物种系统发育的模式
[来源:公有领域]。(Last Universal Common Ancestor 共同祖先;Eukarya 真核(生物)域;Protista 原生生物(界);Plantae植物界;Fungi 真菌界;Animalia 动物界;Archaea 古生菌;Euryarchaeotes 古菌门;Crenarchaeotes 生菌门;Nanoarchaeotes 纳米古菌;Korarchaeotes 科拉古菌门;Thaumarchaeotes 奇古菌门;Bacteria 细菌;Proteobacteria 变形菌门;Chlamydias 衣原体;Spirochètes 螺旋体;Cyanobacteria 蓝藻;Firmicotes 厚壁菌;Actinobacteria 放线菌)

  这一观点与现代科学研究结果完全一致,现代科学研究试图了解这种原始祖先形式的特征,称为LUCA,即共同祖先(Last Universal Common Ancestor)(图5)。关于这个主题,我们可以查阅法国科学院于2013年组织的特别研讨会“生命的起源”的视频[5]

  因此,我们可以看到就生命的起源而言,拉马克和达尔文的理论是基于对生命世界的两种截然不同的看法。

  二者理论之间至少还有另外两个重要的区别。由于二者都涉及生命的进化方式,因此它们交织在一起错综复杂。但为了表述清楚,我们将分别介绍它们。

3.进化转变的机制

  我们现在介绍这两种理论真正的核心内容。拉马克认为,作为物种转化根源的个体变异是外部环境的影响下产生了“需要”,而“需要”本身就是“行动”或“努力”的起源,而这种“行动”或“努力”将成为生物的“习惯”。我们在此引用他的话:“第二个结论是我自己的:它假设环境对生物习惯的影响,然后是习惯对动物身体各部分情况的影响,甚至是对组织状况的影响,每只动物都可以在其身体各部分和组织中发展出可能对其生存非常重要的变化。”

  在《动物学哲学》的第七章中,它陈述了第一条定律:“在任何尚未达到其发育终点的动物中,对器官频繁和持续的使用会使该器官逐渐加强、发展、扩大……;而若这种器官有持续的缺陷,其功能则会在不知不觉中被削弱和减退,进而逐渐减少其功能,最终使其消失”。

  在讨论植物的进化机制时,拉马克则提出了环境对有机体的影响更为直接,因为对于植物而言不存在所谓的努力和习惯!因此,在拉马克的理论中,变化总是或多或少直接在外部条件作用下产生。

  自20世纪初发现基因突变以来,新拉马克主义者不得不在原有理论的基础上整合突变是变异根源这一观点。然后他们认为这些变异必须是特定的基因在环境的引导下产生的,以使有机体适应其环境。但这个想法与自20世纪40年代以来进行的所有实验研究相矛盾。一个美国团队在1997年发表了最新的也是最具示范性的一篇文章[6],我们稍后再讨论这个问题。

  基于这些诱发产生的变异,物种的转变将沿着复杂性增加的趋势变化,至少在动物中是这样。这种趋势将在演变中起到“驱动力”的作用。但这种趋势从何而来?它应该是生物的内在属性,会不可逆转地将生物体的结构变得更加复杂。因此,这是无需解释的自然法则。顺便提一下,按照同样的逻辑,拉马克不相信物种会灭绝,除了那些被人类活动毁灭的物种。他认为,物种的转变是生物自身的复杂化,但生物本身不会灭绝。

  然而,拉马克十分支持唯物主义,并经常强调生命只应遵循物理定律。必须承认,拉马克在他的著作中经常提到“造物主”有一定政治投机的意味(拿破仑不能接受上帝在生命产生和演化过程中完全不起作用!)。然而在他看来,这种不断趋向复杂的趋势,是生物独有的属性,是对生命主义哲学学说的一个特有的强调,该学说确立了一个与思维灵魂和身体的理化性质不同的另一个重要原则,它支配着生命现象(安德烈·拉兰德(André Lalande)的定义)。

  应该注意的是,这种复杂化的趋势,以及环境对生物形态变化的影响,都起到了抵抗外来危害的作用。因此,拉马克主义所表述的物种转化中的随机程度十分有限。这就是他的理论吸引了许多生物学家和科学哲学家的原因。

  而达尔文强烈反对外部条件是引起物种性状改变的原因这一观点。在《物种起源》的导言中,他写道:“自然学家不断将外部条件,如气候、食物等视为变异的唯一可能原因。正如我们将在下文中看到的那样,这可能在一定程度上是真的;但是,啄木鸟的身体结构(例如啄木鸟的脚、尾巴、喙和舌头)非常适合在树皮下捕捉昆虫,将这种高度契合的形成仅仅归因于外部条件是荒谬的。……”他还拒绝一股力量推动复杂性增加的观点,他认为这很“愚蠢”。

  在达尔文理论中,“自发的和偶然的遗传变异发挥主要影响,自然选择也从中起作用(参见图4;参见进化论:误解和抵抗)。正是后者扮演了进化“引擎”的角色,偶然发生的变异只是为进化提供基本的“材料”。达尔文写道:“我相信自然选择一直是主要的但不是唯一的修改手段”。

环境百科全书-生命-物种进化转变的图表
图6.根据拉马克(A)和达尔文(B)总结的物种进化转变的图表。
在拉马克(A1到A3)中,这种转变发生在导致“需求”的外部环境的影响下:在这里,长颈鹿的脖子会变长(箭头),以便它可以以树木的高叶为食。对于达尔文来说,一个物种内“自发的和偶然的”遗传变异将增加其多样性(B1),这就是自然选择的基础:在长颈鹿的例子中,长颈鹿的祖先存在着颈部长短的差异,而环境(树枝的高度)将成为选择的屏障;拥有长颈的个体将更有效地繁殖,因为他们吃得更好(B2)。基于 Solarist的图画绘制的图表(自己的作品)[知识共享许可协议 BY 3.0],通过维基共享资源。[来源:照片©雅克·乔亚德(Jacques Joyard)]

  因此,达尔文的理论所表述的进化过程并不存在任何决定性。偶然发生的变异和选择相结合的结果是,一个种群在给定时间和给定环境中的最佳适应,很大程度上是具有危害性的(见焦点文章进化的起伏:小数量的作用)。就其本身而言,这个过程并不意味着任何复杂性的倾向,更不用说趋于完美了。在此期间生物体可能会获得新功能,但也可能会失去已有的某些功能,从而使身体结构更加简化,这种现象通常在各种寄生虫中被观察到。不用说物种的灭绝,即使整个动物群的灭绝,拉马克都不接受。达尔文进化论者欣然说,如果进化要重新开始,没理由会重复之前同样的路。拉马克和达尔文的观点之间再一次发生了巨大分歧。

4.将变化传递给后代

  让我们回到已经提到的关于后天特征的继承问题上,这个表达通常与拉马克的理论有关,但实际上它的出现要比拉马克的理论要晚得多。这第三点在两种理论之间的差异远小于前一种,但对于遗传学中积累的知识仍然很重要。

  在生物学家或科学史学家的笔下,这种后天特征的继承有时表现为拉马克和达尔文理论之间的类比,有时是它们之间的唯一主要区别。因此,非专业人士很难自行理解,我们在此试着澄清一下。

  首先,让我们回顾一下,在拉马克和达尔文的时代,我们对遗传机制一无所知[7]。所以我们必须试着理解为什么“狗不会生猫”诸如此类的问题。

  由于在拉马克主义中,变异是在环境的影响下发生的,所以它们从一开始就不是可遗传的(今天我们说:它们不是遗传的,而只是表型的)。然而,要让它们在物种的转化中发挥作用,它们必须是可遗传的,因此拉马克第二定律:“由于其种族长期生存环境的影响,自然会导致其失去或获得的一切会一代一代地保留给后代,前提是两性或产生这些新个体的人所共有的。”

  因此,在环境影响下获得的性状将传递给后代。这不是拉马克特有的假设,他采用了一个在他那个时代已经被考虑过的想法,并且自古以来就被认为是不言而喻的,但却与上个世纪进行的研究相矛盾

  达尔文并不完全排斥在环境直接影响下获得的某些性状会遗传的可能。他甚至论述了一个非常古老的假设,即“泛生论”理论(“泛生论”理论是受古代思想启发并由达尔文提出来解释生物遗传、繁殖和发育的假说。非常小的粒子(gemmules)将由不同的身体部位产生并传播到生殖器官。达尔文本人认为这是非常推测性和临时性的。),这种假说甚至可追溯到希波克拉底时代(公元前460-370年)。泛生子假说能够解释一般性的遗传,也可以解释后天特征的遗传。但对达尔文来说,这充其量只能是次要机制。关于泛生论,达尔文认为,这个假设大都是推测性和暂时性的。他认为物种转化过程中唯一有意义的变异是那些可被传递的变异,现在被称为“遗传”(参见稳定性和变异性之间的基因组)。他在《物种起源》的第一章中写道:“任何不可遗传的变异对我们来说都是无关紧要的”。这句话可以被培育新品种的育种者和农艺师使用。

  总之,后天性状的遗传对于拉马克的理论至关重要。从达尔文的角度来看,它则并不是进化论的一部分,尽管达尔文在某些情况下并没有完全排除它。

5.对达尔文主义的多重抵制

  通过对两种理论之间本质区别的简要概述,我们发现它们的基础完全是难以调和的两种看待生命世界的观点(见表)。因此,讨论所谓基于表观遗传现象的达尔文主义和拉马克主义之间的新综合是无关紧要的,只会成为混乱的根源。尽管如此,这些客观存在的现象肯定会丰富综合理论,正如本网站另一篇文章所讨论的那样(参见生物体对环境的适应),但现在说更多还为时过早。

表.拉马克和达尔文思想的一些主要区别
环境百科全书-生命-拉马克和达尔文思想的一些主要区别

  但在这里,我们需要将有关这种倾向的辩论扩大化,以挑战达尔文理论的基本机制。这并不是什么新鲜事,它是自1859年《物种起源》出版以来已经反复出现过的现象,又在20世纪40年代综合理论的发展之后被重新启动。一旦新的实验结果可能同达尔文进化论相悖,记者和科学家就会抓住机会质疑它,即使他们明知道达尔文主义仍是目前的主流观点。

  最近的两个例子则能够证明这种趋势的存在。第一个例子是日本研究员木村资生从1968年开始发表的工作。他于1983年在一本名为《分子进化中性学说》的书中发表了他的工作总结,该书于1990年出版[8]。木村强调,生化技术证明了许多DNA突变在自然选择方面是中性的。当时,记者和生物学家(显然没有读过他的文章)用它来反对新达尔文主义的主题:“所有突变都是中性的,所以自然选择在进化中没有作用”。它是达尔文理论的核心支柱。

  木村资生表达了对这一观点的强烈否认,因为他从未写过所有突变都是中性的。他的工作完全没有跳出达尔文主义的基本理论。他的书中有一整章专门讨论自然选择。其结论现在已经被进化论者和群体遗传学家广泛接受(参见遗传多态性和选择)。

  第二个例子更新,且更有启发性。它基于1987年美国著名遗传学家约翰·凯恩斯(John Cairns)在大肠杆菌中进行的实验。他使用了一种携带有缺陷基因的菌株,该基因会导致营养糖缺乏,这种缺陷会抑制细菌繁殖但不会杀死它们。他观察到,在营养缺乏条件下,反向突变(再次发挥功能的基因)的发生率比正常条件下要高得多。那么自然有理由怀疑这种异常的反向突变率是否是由培养基成分所引发的突变造成的,并且突变会精确地针对有缺陷的基因以使其再次发挥作用。许多实验室已经解决了这个问题,并且一场高水平的科学争论已经持续了10年。

  这场争论在1997年由苏珊·M.罗森伯格(Susan M. Rosenberg)团队的精彩实验一锤定音,前文已经提到过[6]。该团队证明,反向突变之所以会迅速发生是由于营养缺乏诱导产生了异常高的诱变率。但它是作用在整个基因组,而没有针对任何缺陷基因的靶向。这一结果符合新达尔文主义。这种由外界压力条件引发的突变率增加也在本网站的另一篇讨论“SOS反应”的文章中进行了讨论(参见稳定性和可变性之间的基因组)。

  值得注意的是,在争议发生的最初几年,一些所谓严肃的专业科学杂志上发表了针对新达尔文主义的极端恶毒的文章,将其描述为 “一种我们终将摆脱的荒谬理论”。

  我们将注意到,这两类作品所引发的冲击直指达尔文主义和拉马克主义差异的核心:第一个案例中受到冲击的是自然选择理论,第二个例子则质疑了突变的随机性。很难不从中看到对拉马克主义回归的期待,而对表观遗传学的一些反应可能也是出于相同的原因。

  已经提到过的一篇文章为这种对待拉马克进化论观点的热衷提供了解释(参见进化论:误解和抵抗)。一方面,拉马克认为生物会通过自身努力来适应环境,这更符合人们的常识和社会道德,因此更容易被接受。至于生命变得越来越复杂的内在趋势,它可能暗示了某种唯心论(拉马克经常提到“万物的至高无上的作者”以强调这一点),这可能会让那些对达尔文唯物主义不满的人感到安心,毕竟感情和科学很难齐头并进。

 


参考文献和注释

封面图片:有猴子和蛇的热带森林(亨利·卢梭(Henri Rousseau),1910)。[美国华盛顿国家美术馆,公有领域]

[1] “脚下的土地”网站;http://www.lespiedsdansleplat.me/la-montee-en-puissance-des-ideologies-creationnistes/

[2] Pietro Corsi, Jean Gayon, Gabriel Gohau & Stéphane Tirard (2006) Lamarck, philosopher of nature, Ed. PUF

[3] Laurent Loison & Francesca Merlin, “Épigénétique et Théorie de l’Évolution”, Encyclopædia Universalis[online],accessed 22 September2017.URL:http://www.universalis.fr/encyclopedie/epigenetique-et-theorie-de-l-evolution/

[4] 自发产生是一个亚里士多德提出的概念,它认为生物是从无生命的物质中出现,没有上代。这个想法长期以来一直是常识的一部分:人们认为蛆虫是从腐烂的肉中诞生的。早在17世纪这种观点就受到科学家的质疑,直到19世纪(这一观点当时也被称为“异型生殖”)才被废弃。1864年4月7日,在索邦大学“大圆形剧场”的一次公开会议上,路易斯·巴斯德(Louis Pasteur)展示了对这一题目6年研究的成果,并驳斥了自发产生。法国科学院随后正式宣布不存在自发产生。

[5] 法国科学院网站; http://www.academie-sciences.fr/archivage_site/video/v160913.htm

[6] Torkelson J. et al (1997) Genome-wide hypermutation in a subpopulation of stationary-phase cells underlies recombination-dependent adaptive mutation. EMBO J. 16(11):3303-11.

[7] 捷克僧侣和植物学家格雷戈尔·孟德尔(Gregor Mendel,1822-1884 年)首先通过实验确立了生物遗传规律,他的工作与达尔文同时代。然而,孟德尔的作品在1866年出版时并未引起人们的注意。直到35年后,即20世纪初,荷兰人雨果·德弗里斯(Hugo de Vries)、德国人卡尔·埃里希·科伦斯(Carl Erich Correns)和奥地利人埃里克·冯·切马克(Erich von Tschermak)独立重新发现遗传规律,并在孟德尔的理论中得到了验证。在孟德尔之前,遗传学远没有牛顿之前的物理学先进。

[8] Motoo Kimura (1990), Théorie neutraliste de l’évolution, Paris, Flammarion, (ISBN 2-082-11153-9).


The Encyclopedia of the Environment by the Association des Encyclopédies de l'Environnement et de l'Énergie (www.a3e.fr), contractually linked to the University of Grenoble Alpes and Grenoble INP, and sponsored by the French Academy of Sciences.

To cite this article: BREGLIANO Jean-Claude (March 13, 2024), 拉马克和达尔文:两种对待生命世界的不同看法, Encyclopedia of the Environment, Accessed December 9, 2024 [online ISSN 2555-0950] url : https://www.encyclopedie-environnement.org/zh/vivant-zh/lamarck-and-darwin-two-divergent-visions-of-living-world/.

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