Aristotle the zoologist: ‘A’ for effort, ‘D+’ for his ideas about reproduction

Armand Leroi’s reconstruction of Aristotle’s lost diagram of a cuttlefish.
Armand Leroi’s reconstruction of Aristotle’s lost diagram of a cuttlefish.Armand Leroi

It’s always risky to originate a whole new scientific field. On the one hand, you get credit for developing a fresh way of thinking about the world. On the other, it’s a near certainty you’ll commit some major mistakes that will appear laughable to future minds.

Such is Aristotle’s lot when it comes to zoology. We associate the famed ancient Greek philosopher with his writing on ethics and politics, but he was also a keen observer of the natural world. He spent considerable time on the island of Lesbos in the fourth century BC, observing and dissecting animal life, and collected his ideas in a nine-volume book called the “History of Animals.”


“It’s a wonderful book, big, stuffed full of facts about animals — where they live, how they breathe, what they eat. Some of it is brilliant and insightful and true and some of it is rather strange,” says Armand Leroi.

Leroi is a professor of evolutionary biology at Imperial College, London, and the author of a new book, “The Lagoon: How Aristotle Invented Science,” that reconstructs Aristotle’s early zoological investigations. In an interview, Leroi explained that Aristotle was primarily interested in comparing the parts of different animals in order to figure out how whole organisms work.

“For example, [Aristotle asks], why do some birds have long legs and long bills and other birds have bills suitable for tearing up water plants and webbed feet? He’s thinking that looking at the association between these parts, what we now call the correlation matrix, will allow him to create a causal model for why things are the way they are.”

Armand Leroi’s reconstruction of Aristotle’s lost diagram of an embryonic cuttlefish.
Armand Leroi’s reconstruction of Aristotle’s lost diagram of an embryonic cuttlefish.Armand Leroi

As far as we know, Aristotle was the first person to realize these kinds of big questions could be answered by the careful collection and analysis of data. He also brought a fair amount of intuition and myth to bear on this work, and that is where he made his biggest mistakes. Leroi explains Aristotle believed that “European bison defecate caustic feces that can burn the hair off dogs that are chasing them” — likely a hunter’s tale Aristotle had heard. Also, in typical fashion, he couldn’t figure out what women contributed to reproduction, and concluded that the sperm did most of the work of creating a new person.


“Where he’s brilliant is not so much in the details of his physiology. He’s brilliant in the structure of his thought,” says Leroi. He credits Aristotle for understanding that organisms have a complete physiological system that keeps them alive (Aristotle called this system the “soul”), and for bucking the conventional wisdom about how embryos develop: Other budding naturalists thought embryos were assembled out of tiny representative parts; Aristotle cracked open a chicken egg and recognized that new life actually forms from raw matter.

More than 2,000 years later, we’re inclined to be generous to Aristotle’s science. When you’re trying to understand embryology thousands of years before the microscope is invented, it’s really the effort that counts — and we can thank Aristotle for being among the first to show us that in this realm, the exertion is worth it.

Kevin Hartnett is a writer in South Carolina. He can be reached at kshartnett18@gmail.com.