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Aristotle’s Work in Zoology and Meteorology

Although Aristotle’s work in zoology was not completely accurate, it was the greatest biological investigation of its time, and his work remained the ultimate authority for many centuries after his death. His knowledge of the anatomy of octopus, crustaceans, and many other marine invertebrates are remarkably accurate, and could only have been determined through first-hand dissection. He also described the embryological development of a chick, distinguished whales and dolphins from fish, described the social organization of bees, and observed that some sharks give birth to live young - his books on animals are filled with similar observations, some of which were not confirmed until many centuries later.

Aristotle’s classification system grouped together similar animals into genera, which is much broader than our present day genus, and distinguished species within those genera. His classification divided animals into two types: those with red blood and those without; these divisions correspond closely with our modern vertebrates and invertebrates. The “blooded” animals, corresponding to the vertebrates, included five genera: viviparous quadrupeds (mammals), birds, oviparous quadrupeds (reptiles and amphibians), fishes, and whales (which Aristotle did not realize were mammals). The “bloodless” animals were classified as cephalopods (such as the octopus), crustaceans, insects (which included the spiders, scorpions, and centipedes, in addition to what we now define as insects), shelled animals (such as most mollusks and echinoderms), and "zoophytes," or "plant-animals," which supposedly resembled plants in their form - such as jellyfish and corals.

Aristotle's thoughts on earth sciences can be found in his book Meteorologica. Although the word today means "the study of weather," Aristotle used it to encompass all of the earth sciences, including the studies of the atmosphere and oceans. He deduced the components of the water cycle: "Now the sun, moving as it does, sets up processes of change and becoming and decay, and by its agency the finest and sweetest water is every day carried up and is dissolved into vapour and rises to the upper region, where it is condensed again by the cold and so returns to the earth." He discusses winds, earthquakes (which he thought were caused by underground winds), thunder, lightning, rainbows, and meteors, comets, and the Milky Way (which he thought were atmospheric phenomena). His model of Earth history sounds startlingly like our modern conceptions:

"The same parts of the earth are not always moist or dry, but they change according as rivers come into existence and dry up. And so the relation of land to sea changes too and a place does not always remain land or sea throughout all time, but where there was dry land there comes to be sea, and where there is now sea, there one day comes to be dry land. But we must suppose these changes to follow some order and cycle. The principle and cause of these changes is that the interior of the earth grows and decays, like the bodies of plants and animals. . . .

“But the whole vital process of the earth takes place so gradually and in periods of time which are so immense compared with the length of our life, that these changes are not observed, and before their course can be recorded from beginning to end whole nations perish and are destroyed.”

Aristotle believed that the universe was eternal; it never had a beginning or an end. This is where he differed most from medieval and modern scientists. Change was cyclical to Aristotle; although water might evaporate and rain down again, or rivers might come into existence and then perish, overall the world would never change.

Although Aristotle's pioneering Meteorologica was the first attempt to condense all of meterology into one cohesive subject, it is unlikely he greatly affected those communities whose weather forecasting combined memories of the local climate, dubious weather lore, and perhaps the opinion of an oracle. Nonetheless, Aristotle's great work served as the definitive Western meteorological textbook until scientific developments in the mid-15th century challenged many of his theories.

About the photo: This image is of a famous galaxy (M31) that appears within the constellation Andromeda. It is a spiral galaxy, like our own Milky Way. M31 is one of the farthest objects that can be seen with the naked eye, and was first described by 10th century Persian astronomer Al-Sufi. The knots of blue-white patches in the outer arms are newly formed stars.

image © Thomas V. Davis

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