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This chapter uses the phylogenetically controlled comparative method to test empirically for adaptation in the flight morphology of birds. Comparative data on the morphology, ecology, and behaviour of 450 species are collected from the literature, and used to test how flight morphology relates to flight ecology and behaviour. For each species, a set of ecological characters associated with different aspects of flight performance is scored in binary fashion from the species accounts contained in the most detailed regional handbooks. Generalized least squares analyses are used to identify the statistically significant relationships that exist between flight morphology and flight ecology and behaviour when controlling for phylogeny. The results of this analysis are consistent with the directional predictions made in Chapter 6 about how flight morphology should respond to selection for specific aspects of flight performance. Body mass is predicted by whether a species soars over land, flies in clutter, or hunts by sallying. Controlling for body mass, there are also significant effects of flight ecology and behaviour on wing area and aspect ratio in birds that soar or that submerge fully to feed. These changes in wing morphology involve changes in wingspan in birds that soar exclusively over the sea, but also involve changes in chord in birds that soar over land or submerge fully to feed. Nevertheless, some conspicuous ecological characters, notably the use of migration, have no statistically significant effect on flight morphology. This is presumably due partly to the trade-offs that exist between different aspects of flight performance.

This chapter addresses how we can talk about macroevolution without lapsing into teleology, and shows that the principle of the conditions for existence can play a key role here, first discussing how natural selection enters into explanations of macroevolutionary changes. It then looks at a simple example of macroevolution—evolution of bird flight—and considers the question of how the process of evolutionary adaptation should be represented. In particular, the chapter addresses how the role of narrow sense natural selection and of the conditions for existence in this process should be represented.

This chapter combines dimensional analysis with simple physical reasoning to make directional predictions about how biomechanical performance should vary with morphology, using bird flight as an example. Deriving the predictions from first principles like this allows them to be made as general as they possibly can be, although they are extended later under a more restrictive set of aerodynamic assumptions with the aid of detailed wing theory. A higher-order lifting line theory is presented, which predicts the lift coefficient on an elliptically loaded wing to within 1% of the exact solution for wings of aspect ratio ≥2.55. Although this higher-order asymptotic approximation is much more accurate than classical lifting line theory at low aspect ratio, it does not appear to have been used previously in biomechanics. The results of these analyses are used to derive a set of directional predictions about how flight morphology is expected to change in response to natural selection for specific ecologically relevant aspects of flight performance, including high transient force production, high glide speed, low sink rate, low aerodynamic power requirements, and high aerodynamic efficiency. The resulting predictions are not new, but they are gathered here in one place to show how selection for conflicting aspects of performance is expected to lead to morphological trade-offs. These directional predictions all relate to easily measurable aspects of flight morphology, including wing area, wing loading, and aspect ratio, and are tested empirically for a very large dataset of birds in Chapter 7 using the phylogenetically controlled comparative method.

Chapter Seven continues the argument from Chapter Six about maternal seduction and its derivatives. It considers Freud’s thesis of the rival sublimations of Leonardo’s infantile sexual fantasy into, first, his uniquely advanced scientific investigations, especially those into the flight of birds with its accompanying ambition to be the first man to fly, and, second, his painting with its unfinished works and its temporary abandonment for science. It examines Freud’s commentary on the Mona Lisa, the Virgin and Child with St. Anne and its preparatory London Cartoon, and the late paintings of Bacchus and St John the Baptist, and considers the phenomenon of the fused maternal group of the Virgin and St. Anne in the Louvre painting and the London Cartoon and Laplanche’s development of Freud’s argument about the work of defusion, which it relates to the question of sublimation. Finally it addresses the effects of the return of maternal seduction in psychoanalytic reflection in the motif of the reverse Oedipus and Freud’s extraordinary catharsiscelebration of the figures of male femininity in the Bacchus and St. John with their “secret of love”, “about which silence must be kept”.