Monday, February 20, 2017

Aristotle And Darwin: Why?

A thought provoking passage from The Lagoon: How Aristotle Invented Science by Armand Marie Leroi-

The history of Western thought is littered with teleologists. From fourth-century Attica to twenty-first century Kansas, the Argument from Design has never lost its appeal. Aristotle and Darwin, however, share the most unusual conviction that though the organic world is filled with design there is no designer. But if the designer is dead for whose benefit is design? It's the prosecutor's question: cui bono?

Darwin answered that individuals benefit. Biologists have batted the question about ever since. The answers they've essayed are : memes, genes, individuals, groups, species, some combination or all of the above. Aristotle, however, generally appears to agree with Darwin: organs exist for the sake of the survival and reproduction of individual animals. This is why so much of his biology seems so familiar.

Yet there is a deep difference between Aristotle's teleology and Darwin's adapatationism, one which appears when we follow the chain of explanation that any theory of organic design invites. Why does the elephant have a trunk? To snorkel. Why must it snorkel? Because it's slow and lives in swamps. Why is it slow? Because it's big. Why is it big? To defend itself. Why must it defend itself? Because it wants to survive and reproduce. Why does it want to survive and reproduce? Because..

Because natural selection has designed the elephant to reproduce itself. Darwin gave teleology a mechanistic explanation. He halted the march of whys.

Aristotle was an eternalist. In his cosmos, organic beings were produced by a union of their parents. They in turn by a union of their parents.. continued into infinite regress. Organisms wanted to survive and reproduce so that their "kind" persist for ever. This static world had always existed. He saw divinity in immortality.

In Aristotle's world organic beings don't change and transform into anything else. He never did come around proposing a theory of transmutation or change or evolution. He had some of the raw material to advance such thoughts.

His extensive dissections and comparative anatomy had given him an understanding that life is arranged in a hierarchical manner. Dogs and foxes are more closely related to each other than either is to lions and leopards. Both, canids and felines though are part of a larger mammal family. Members within this family are more similar to each other than they are to members of reptiles. Aristotle recognized that there are groups within groups. He termed the basic taxonomic units as genos. These are part of the larger magiste gene. Ikthis (fish), entoma (insects),ornis (birds), zootoka tetrapoda (live bearing tetrapods- mammals), oiotoka tetrpoda (egg laying tetrapods -reptiles, amphibians) were some of his "greatest kinds" or  magiste gene.  Yet, he didn't ponder upon the relationship between life's groupings and never realized that this pattern is a tree like structure, resulting from common ancestry and subsequent lineage branching. The figure to the left is Darwin's sketch (Notebook B 1837) of the tree of life depicting common ancestry and the branching nature of life.

Aristotle was aware that there is variation within each "kind" or genos. Organisms within a genos varied in their eidos or form. He also had a theory of inheritance. Parents passed on their eidos to progeny, often not exactly. Progeny then, occasionally, could be somewhat different from parents. Moreover, his understanding of inheritance was surprisingly modern. A child might inherit her father's nose or her mother's nose but not something in between. So, he had a particulate view of inheritance. This also meant that traits remain stable and may pass on unaltered over many generations.  Father's and mother's contributions don't blend to form some average feature, but remain discrete. By this he did not mean that actual particles were being transmitted. Rather, traits were reproduced by the movement and heat of either the semen or 'menses' (menstrual fluid). Whichever was stronger determined whether the child resembled her father or mother.

Darwin never understood inheritance very well. He was sure that variation is the  fuel of evolution. But he was troubled that blending would wipe out variation in populations. He struggled with the problem of inheritance for decades.

Aristotle's limitation was that he didn't think anomalous features or differences offered any advantages to the individual. His view was that creatures are born within the limits of their physiology and there was no room for improvement. In that, he should have listened to Socrates! In a Greek society with very particular notions of beauty, Socrates, with his snub nose and flabby lips was an anomaly. He boasted though that his lips worked better than anyone else's. The mutant feature provided an advantage. Aristotle rejected such notions.

Perhaps this is why he couldn't take the next step.... That advantageous variation could be selected upon by nature. Possessors of that trait would on average leave behind more progeny. A certain new form would thus become more common over generations and while some other form disappeared. Some people argue that the lack of a fossil record may have been one reason why Aristotle never appreciated that organic beings have changed over time. However, as Leroi describes, Greek travelers and physiologoi (naturalists) from his time had written about fossil sea shells found high on mountains and fish imprints on stone. Theophrastus, his student and protege, describes dug up ivory. Dwarf elephants were among the many remains from the Pleistocene megafaunal fossil beds of Samos, Kos and Tilos islands.

To someone wedded to an unchanging cosmos, this may not have made any difference, Leroi argues.

It would be more than two millennia before Darwin and Wallace put all the pieces together.

Highly Recommended.