Methodology
This chapter engages two key components of the philosophy of biology: adaptationism and phylogenetics. At the heart of this chapter is an argument for a conceptual/methodological distinction between the evolutionary origin and maintenance of traits as it pertains to ultimate causation. The authors argue that phylogenetics–or biological development–as is operational within the ontogenetic process (the process of becoming)– is the best explanation for the appearance of novelty whereas adaptation is limited to action upon an already existing trait.
This distinction–between origin and maintenance–is important because it delineates and defines the function of an adaptionist approach while simultaneously hedging it from resurgent criticism. One such criticism, for example, suggests that the adaptationist program is so pervasive that almost anything can be defined as an adaptation. In other words, a story about why such and such a trait came to be can be constructed for virtually any trait, and even if said story can be proven to be untrue, another story can readily supplant it without calling into question the issue of adaptationism as a whole. The authors argue that the role of an adaptationist approach is to distinguish between selected and unselected traits, and more specifically, directly or indirectly selected traits. Adaptationsim can only work on what already exists thus its explanatory power is rather specifically limited.
Using phylogenetics in conjunction with homology (a cross-species comparison of similar-looking traits), and keeping the principle of parsimony in mind, evolutionary origins within the Tree of Life are reliably ascertainable. The authors are careful to point out that indication of a shared ancestral lineage does not necessarily equate to the transposition of the studies of other primate sexuality to human sexuality, even though there might be some benefit to such considerations.
