Thread by @ed_hagen

1. @itsbirdemic recently critiqued evolutionary psychology:

kevinabird.github.io/2020/04/27/Evo…

Bird correctly notes that EP (1) focuses on complex adaptations and (2) holds that these always arise from natural selection.

2. Bird, drawing on Lynch (2007), claims that (2) above is false: "Work from Michael Lynch (2007) directly challenges the view that complexity requires adaptive explanations...."

pnas.org/content/pnas/1…

3. But "complexity" is much more general than complex adaptation (complex design). The weather is complex. The orbital motions of Saturn's moons are complex. The distribution of bubbles in bubble bath is complex. The wrinkles in my skin are complex. None of these exhibit design.

4. I agree with Lynch that natural selection does not necessarily favor complexity, and that much organism "complexity" is not due to natural selection, both of which are irrelevant to the claim that complex *design* is explained by natural selection.

5. Adaptations (design): the functional, purposeful parts of organisms, whose structures are explained by their fitness-enhancing effects, e.g., the structure of the heart is explained by its pumping function.

Complex adaptations: adaptations with many "parts", e.g., the heart.

6. Major question across the millennia: How to identify & explain the "purposeful", functional parts of organisms?

7. There is a pretty straight historical sequence from [Plato] -> Aristotle -> Galen -> Harvey [& many scholars whose names I don't know] -> Paley -> Darwin -> GC Williams -> EP

8. Plato (the Über "Panglossian"): The order and beauty of the universe is the product of an intelligent, divine "Demiurge" (craftsman), that is "as excellent as its nature permits it to be":

plato.stanford.edu/entries/plato-…

9. Aristotle: Does not invoke a divine Demiurge. Instead, some beneficial or harmful phenomena, such as the effects of rain on crops, are explained by blind necessity or chance (Physics II 8):

10. Aristotle con't: The "purposeful" parts of animals, on the other hand, because they reliably occur in all members of a species, cannot be explained by blind necessity or chance.

11. Aristotle con't: Rather, they are recognized by their evidence of design to benefit the animal itself:

12. Aristotle con't: And such reliably developing, purposeful parts of organisms are explained by final causes (key idea: there must be a causal connection between the formation of the teeth and the needs of the animal):

plato.stanford.edu/entries/aristo…

13. Galen: Synthesizes Plato & Aristotle. Divine Craftsman explains organism design & purpose (Plato), but these benefit the organism itself, & must also be understood as products of material (Aristotelian) causes:

plato.stanford.edu/entries/galen/…

14. Galen -> Harvey: mechanical and teleological accounts of biological phenomena are compatible (similar to our modern proximate and ultimate distinction):

15. Paley: Like Galen, Paley engages with the anatomical and physiological details of many specific organisms to show evidence of functional design.

16. Paley: The source of organism design, as for Plato & Galen, is a divine Craftsman (God), but like Aristotle & Galen, the parts of organisms are designed to benefit the organism itself. Emphasizes that purposeful parts of organisms are *adapted* to the organisms' environments:

17. Darwin: Was heavily influenced by Paley:

18. Darwin: Tackles the problem of design and provides the modern explanation of its origins as a consequence of the differential reproduction of heritable variation (natural selection):

gutenberg.org/files/1228/122…

19. Evolutionary biologist GC Williams: Reminds biologists of the important distinction (identified by Aristotle) between incidental effects, however beneficial, and organism design (from Adaptation and Natural Selection, 1966):

20. GC Williams (1966): Also reminds biologists that the "central biological problem is not survival as such, but design for survival":

21. Symons (1979): Basically invents EP by applying Williams (1966) to human psychology (from The Evolution of Human Sexuality):

22. Evolutionary geneticist David Haig (2007): Argues that even epigenetic optimization ultimately depends on natural selection (e.g., genetically evolved learning mechanisms):

haiggroup.oeb.harvard.edu/files/haig/fil…

23. But what about genetics? Given that it has taken a lifetime of research for Davidson and colleagues to elucide the gene regulatory networks (GRN) that govern the first few hours of sea urchin development...

echinobase.org/endomes/

24. ...we are probably decades away from understanding the GRNs underlying the development of any complex human organ, especially since acquiring such understanding has generally involved manipulating GRNs during development (a huge no-no for human embryos).

25. Evolutionary biologist Hammerstein (1996): Fortunately, study of adaptations can often ignore genetic details.

To conclude: EP's focus on complex adaptations has deep intellectual roots & is solidly in the mainstream of modern evolutionary biology.

link.springer.com/article/10.100…