Studies in the Theory of Descent, Volume II

This volume offers a thoughtful look at how the different stages of an insect’s life—egg, larva, pupa, and adult—relate to one another. Drawing on careful observations, it asks whether the size and form of a butterfly are strictly tied to the amount of material in its caterpillar, or whether each stage can vary on its own. The author contrasts clear cases of independence with examples where external pressures, such as “nurse‑breeding” in certain flies and wasps, push stages to adapt together. The discussion is framed by a brief prefatory note from a famous naturalist, grounding the work in its historic scientific context.

The text then turns to the concept of variability, describing how some species show dramatic changes in one stage while remaining stable in others. Seasonal dimorphism in caterpillars, the constant appearance of adult butterflies, and the occasional matching changes across all stages illustrate this point. By examining these patterns, the author highlights how individual fluctuations can eventually give rise to new, stable forms. Listeners will appreciate the clear explanations and vivid insect examples that make this classic evolutionary study both accessible and fascinating.