Lamarck proposed two “Laws”, which was the aim of every scientist of the time; to make laws that paralleled Newton’s great laws of physics. His first law was use strengthened of an organ and disuse weakened it. If an organism failed to make use of its parts, then those parts would disappear. His second law was that everything that nature caused to be acquired or lost by individuals because of the conditions they had been exposed to over a long time would be conveyed to new generations. In short, the species would “learn” from experience. This would be enough to cause organisms to evolve. But he also thought that they were impelled to become more perfect over time by a “subtle fluid” that had an innate tendency to drive this improvement by purely physical means. Many later thinkers believed, in part because of the mistranslation in to English of his words, probably by Lyell, that he thought that these changes could be brought about predictively – that a giraffe could “strive” to reach leaves at the top of a tree and so pass on a slightly longer neck to its progeny. This is wrong; but it remains a sense in which people think of things as Lamarckian.
Despite the objections already made to spontaneous generation of living things from non-living material, Lamarck thought that simple forms (not, for example, more advanced forms like flies or mice) were continually appearing. Over enough time, they became advanced forms. Each of these forms was a single lineage. Initially he didn’t think that they branched off to become different forms; in true Chain style he thought they all followed the same pathway but as he worked out his view of adaptation by use and disuse he realised that forms would change in different ways. By 1809 he was prepared to admit many different branches, but always an increase in organisation.
Peter Bowler gave this figure to explain Lamarck’s progressivism. The scale of organisation, or the graded chain, at any one moment is filled by organisms that have their own distinct history. Humans evolved, in his opinion, from older ape forms, but not from the present apes, nor did apes and humans share common ancestors. When we have evolved further, apes will evolve to fill the “human grade”.
Two kinds of evolutionary thinking
Two kinds of evolutionarythinkingDarwinism and Lamarckism
John WilkinsMay 22, 2013Some quotes“Evolution is so simple, almost anyonecan misunderstand it” – David Hull“Natural Selection is not Evolution ” –Ronald A Fisher“Nothing in biology makes senseexcept in the light of evolution” –Theodosius Dobzhansky
John WilkinsMay 22, 2013Star Trek Evolution Why is it sopopular? Where doesthis idea comefrom? What shouldwe think aboutevolution?
John WilkinsMay 22, 2013The popular version Grades Direction Perfection Steady Humans are the goal
John WilkinsMay 22, 2013The scientific version Branches Randomness + selection Irregular No direction but locally Humans are one animal amongmany
John WilkinsMay 22, 2013Names The popular version is called many things: Great chain of being Ladder of progress Lamarckism The scientific version is also called manythings: Darwinism Neo-Darwinism The Modern Synthesis
John WilkinsMay 22, 2013Progress Depends on the “target” Jacob’s Ladder - God at the top,something ugly at the bottom Evolution has always been thoughtto be progressive Until Darwin (and even then)
John WilkinsMay 22, 2013There are two kinds ofevolution The one Lamarck developed andmade known. The one Charles Darwin developedand made known Only Darwin’s is truly novel, and yetit is the least well known, and so ittakes the longest to really “get”.
John WilkinsMay 22, 2013Before evolution Western thinking was historicalbecause of Christian theology, butchange tended to a goal Everything was ranked from lowestto highest Higher things were “more perfect”than lower things
John WilkinsMay 22, 2013The medieval viewStones … mere beingFire … + motionPlants … + growthAnimals … + senseMan … + reasonHeaven … + incorruptibilityAngels … + knowledge of goodGod … with the lot + perfectionRaymond Lull, 1512
John WilkinsMay 22, 2013The chain was also moralBovillus 1510
John WilkinsMay 22, 2013Great chain of being A view that goes back to the Greeks Everything is lined up along a scale Made into a time series in the 17thand 18th centuries Lamarck one of the firstevolutionists, and followed thisview
John WilkinsMay 22, 2013Three “Lamarckisms” That changes to individualorganisms are likely to be inheritedor will affect the hereditability oftraits. That things evolve on apreprogrammed pathway toperfection That change is predictive of theneeds (or wants) of organisms
John WilkinsMay 22, 2013Lamarck’s scale from lower tohigher At first a single scale Later, two, one for invertebrates,one for vertebrates Each “species” underwent changeup the scale
John WilkinsMay 22, 2013Lamarck’s view of evolution
John WilkinsMay 22, 2013Spontaneous generation Lamarck accepted the constantgeneration of living things in theirsimplest form, from the non-living Each new spontaneous generationstarted a lineage Each lineage would evolve through thesame stages as the earlier ones had Later, he allowed for some branching
John WilkinsMay 22, 2013Lamarck’s view of evolution 2
John WilkinsMay 22, 2013Bees and brains “It is absurd to talk of one animal beinghigher than another – We consider thosewhere the cerebral structures intellectualfaculties most developed, as highest. – Abee doubtless would where the instinctswere.” Charles Darwin, Notebook B “Never say ‘higher’ or ‘lower’” Darwin What about the flowers? What would theysay?
John WilkinsMay 22, 2013Darwin’s view Things get better locally, not globally Being “fitter” is a matter of being able to dowell then and there only Populations, not whole species, evolve Evolution branches all the time Everything has evolved as much aseverything else!
John WilkinsMay 22, 2013Branching evolutionNo real progress here
John WilkinsMay 22, 2013The tree of life is a coral tree
John WilkinsMay 22, 2013Darwin used the tree metaphor This, too could be misused Although Darwin’s tree was notdirectional at first, others came tobe
John WilkinsMay 22, 2013Haeckel’smightyoaksCentral trunk leadsdirectly to humans,and everything onthe trunk issomehow“important”
John WilkinsMay 22, 2013IndirectprogressionismPatten (1925) makes adirect line througharthropods (bugs) tovertebrates (non-bugs)
John WilkinsMay 22, 2013Indirect racismNotice how the earlier (and“less evolved”) forms areshown at the left of thediagram. Now notice the“races” of Homo - in order,African (i.e., the “Negro”),Australian (aboriginal),Mongolian (the “Asiatic”),and of course theEuropean.Diagram c1920. There wasno geological evidence atthe time (or now) of any ofthis.
John WilkinsMay 22, 2013Intelligence stillat the top of thechain…Despite the divergence ofevolution until now, Teilhard(1955) still thinks that it willall come together with humansas the final players. At least heisn’t racist about it – all“socialised” humans will evolveto the Omega Point.
John WilkinsMay 22, 2013Missing links and ancestors
John WilkinsMay 22, 2013Missing links and ancestors
John WilkinsMay 22, 2013Any ancestors at all? We cannot be sure that a fossil orliving species is actually anancestor Might be a sibling of the ancestor Might be the ancestor, but how totell? At best, we have likelihoods
John WilkinsMay 22, 2013Populations All evolution happens topopulations Not individuals (that’s “development”) Not entire species (that’s“speciation”) Not larger groups (that’s artificial)
John WilkinsMay 22, 2013Natural selection Does not equal “evolution” Is the process of adaptation (ofpopulations) Is not all that happens in evolution(that’s called “panadaptationism”)
John WilkinsMay 22, 2013SelectionFollows the fitnesspeaks (available ways tomake a living).They have to bereachable, and theyhave to be better thanwhat is already in place.Changes the frequencyof genes in populations.
John WilkinsMay 22, 2013Lessons to be learned Progress is not necessary There is no “next step” Selection is not all there is toevolution Everything is as evolved aseverything else
John WilkinsMay 22, 2013Further reading Bowler, Peter J. Evolution: The History of an Idea. Berkeley:University of California Press, 1984. Dennett, Daniel C. Darwin’s Dangerous Idea: Evolution and theMeanings of Life. New York: Simon and Schuster, 1995. Jordanova, L. J. Lamarck, Past Masters. Oxford; New York:Oxford University Press, 1984. Lovejoy, Arthur O. The Great Chain Chain of Being: A Study ofthe History of an Idea. Cambridge, Mass.: Harvard UniversityPress, 1964 (1936).
A particular slide catching your eye?
Clipping is a handy way to collect important slides you want to go back to later.