Aristotle was a categorizer; probably the first one to break animals into categories like genus and species. We still use these categories today. Noticing certain similar attributes of animals and recognizing relation seems to be just logical. That being said, the relationship is not so clear. We certainly can see the similarity between a fox and a German Shepherd, but the differences are still pretty striking, nonetheless. The genus is called Canis which is simply the Latin word for dog. Canis would be a grouping that Aristotle would call universal. The category “animal” would be even more universal; it includes humans as well.
Much debate occurred regarding these categories among the Scholastics. Generic universals are not clearly a numerical one. They consist of individuals that exist alone, and their relationship often was seen as being more a product of rationality, not as an apparent unity. But it certainly gave way to a lot of debate. Is the generic unity a product of greater metaphysical life or soul that unites all of these? Disparate things can function as a unity. My eyes are not like my ears. My sense of touch is not my sense of smell. Syllogistically, while A (eyes) and B (ears) are disparate, they exist in a greater C, that is, a sort of bodily universal. My body is universal in the sense that it contains a plethora of disparate parts that work together in a complete organism. What makes these function as a unity? I could give a lung and part of my liver to someone else, but that won’t make them me. I could die and another person could be given my heart, but that person still wouldn’t be me. It is more apparent that a body is a unity than humanity would be a unity; but some relationship between every human being is undoubtedly there; but what might unite us is not as clear. People have often been struck by flocks of birds and schools of fish. They will behave in a way that suggests a unity. All human beings share basic biology, but how they may function as a unity would be far more complex than the preceding examples.
Aristotle and the writers that are included in this book had no clue about genetic information. We now know that all the similarities we see among creatures are due to DNA and the information encoded in it. But they could still intuit that there was something that they often referred to as form and/or substance that was shared by creatures. The degree that this was debated is quite impressive, even if the pages devoted to it that you find here make for fairly dull reading.
This is an interesting book to a degree. No worthwhile conclusions are really to be had as far as I could tell after finishing it. Much of this book is devoted to Duns Scotus and Ockham; Porphyry, Abelard and Boethius to a lesser extent. They spend an inordinate amount of time trying to refute some other philosopher. It is an important philosophical topic, and I would say spending some time investigating it is essential to a broad view of philosophy. One can certainly see how the philosophical topic itself was influential for the Idealists, but I would be lying if I said that this book was really engaging. The Scholastics shared a very particular trait with their master: a tendency for pedantic quibbling that is tiresome to labor over. I had intended to read Duns Scotus more after finishing this, but this bored me to tears and I am going to have to change my reading selection until I am ready to revisit the Scholastics. I tried to make the topic a little more engaging in my own words above. At least one can see the merits of the topic a little more easily if one views it the way I laid out, I think. I give the book about 3-and-a-half stars. The topic is important, but I doubt many would be moved by the presentation.