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Emanuel Margoliash was a biochemist whose work on cytochrome c connected protein primary structure, molecular function and evolution. He isolated and sequenced the protein from different organisms and helped develop comparisons of amino acid sequences as evidence for phylogenetic trees.^[ref]

His 1963 paper, Primary structure and evolution of cytochrome c by Emanuel Margoliash, made the structural comparison itself a source of evolutionary evidence. Subsequent collaborative work assembled a tree from twenty cytochrome-c sequences, combining published sequences with measurements from his laboratory.^[ref]

A toy example shows the measurable idea. Align the five-residue strings ACGKT and ACGRT: four positions agree and one differs, giving an observed mismatch fraction $1/5=0.2$. These are invented strings, not Margoliash's data. An observed mismatch count is not automatically elapsed evolutionary time: repeated substitutions can hide earlier changes. The power of the approach is to make molecular resemblance explicit and test competing explanations, while retaining the distinction between sequence observations and an inferred history.

Indrani Mukharji is the author of a 2020 scientific memoir of Emanuel Margoliash. The memoir explains how work on cytochrome c connected protein chemistry with the reconstruction of evolutionary relationships. It follows the isolation and sequencing of the protein through to comparisons between species, showing how a laboratory material became evidence for evolution.^[ref]

One concrete example is the assembly of a phylogenetic tree from cytochrome c sequences for 20 species. The useful idea is to compare corresponding positions in the same protein, rather than treat every difference between organisms as an unrelated observation. Indrani Mukharji's contribution here is documenting and explaining that scientific history; authorship of the memoir is distinct from authorship of the earlier experiments it describes.^[ref]