It had been well established by the 1920s that human and chimpanzee bloods were more similar to one another than horse and donkey bloods were. This was not particularly unfathomable, since humans and chimpanzees are rather similar, after all, but the special similarity of their blood was well known in educated circles at the time of the Tennessee “Monkey Trial” in 1925.

The similarity of the blood of humans and great apes remained an interesting fact until the 1960s, as the molecularization of biology was proceeding, and genes were shown to be linear instructions for the production of proteins, and proteins were shown to be long chains of amino acids. And when you painstakingly sequenced the 287 amino acids of human hemoglobin and gorilla hemoglobin, showed biochemist Emile Zuckerkandl in 1963, you found them to differ in only one or two places, for a difference of less than 1%.