Biological trait identity: modularity, levels, and adaptation

Biological organisms are integrated ensembles of traits, which
comprise parts and properties in different body regions and levels of
organization. A longstanding idea in evolutionary theory is that traits
must be able to change quasi-independently of one another if
organisms are to evolve complex adaptations. Conversely, the
assumption that certain traits are adaptive has been criticized as
presupposing that those traits possess a degree of independence or
“modularity” that is biologically unrealistic. These arguments
converge on a common, rarely questioned assumption that the true
traits of an organism are determined by the modular organization of
its genetic system. In this project we propose to systematically reexamine
the neglected question “what is a trait?” in light of recent
models of genetic architecture that complicate the modular picture of
organisms. We propose to develop a conceptual account of trait
individuation that is compatible with non-modular traits, and with
complex overlaps, nestedness, and dissociations between traits and
modules across multiple levels of organization, while also integrating
this new perspective with what is right about the modular view. These
investigations promise to shed new light on the classic theme of
adaptationism, suggesting that the more intuitive integral picture of
the organism is more compatible with adaptability and evolvability
than previously appreciated.