The Spandrels of San Marco and the Panglossian Paradigm: A Critique of the Adaptationist Programme, hereafter called The Spandrels, is an article written by Stephen J. Gould and Richard C. Lewontin published in the Proceedings of the Royal Society of London in 1979. The paper emphasizes issues with what the two authors call adaptationism or the adaptationist programme as a framework to explain how species and traits evolved. The paper is one in a series of works in which Gould emphasized the role of development in evolutionary theories. The article suggests that constraints on how organisms can develop and constraints on how species can evolve from others play a central role in explaining the how species and traits evolve. The authors note that organisms from different species develop as embryos through stages similar across species, genera, and higher classes. Gould and Lewontin hypothesize that those stages constrained the possible pathways of evolution and has therefore guided the history of life. Throughout the paper, the authors rely on analogy of some parts of organisms to architectural structures called spandrels, marked in this image as 'a'."

Mutual Affinities of Organic Beings: Morphology: Embryology: Rudimentary Organs is the thirteenth chapter of Charles Darwin's book The Origin of Species, first published in England in 1859. The book details part of Darwin's argument for the common ancestry of life and natural selection as the cause of speciation. In this chapter, Darwin summarizes the evidence for evolution by connecting observations of development in organisms to the processes of natural selection. Darwin shows how the theory of special creation, which claims that God directly created all organisms in their current form, is inferior to the theory of natural selection for its ability to explain the diversity of life. In this chapter, Darwin also discusses classification and homology as they relate to natural selection.