The activities undergone by living things are paradigmatically end-directed, and so this chapter examines Aristotle’s invocation of teleological notions (as well as their contrast with non-teleological notions) in his scientific investigation of life. In particular, the chapter looks at how Aristotle explains why various processes occur, why some kinds of organisms have (or lack) certain parts or features, and why those parts or features vary in their sizes and shapes. Aristotle’s biological explanations are complex and rich in detail, thus providing valuable resources for making headway into some of the interpretive challenges facing our understanding of his distinctive form of natural teleology – one that countenances purposes in the absence of intentions and volitions, and one that finds the occurrence of necessity compatible with goal-directedness.

Aristotle wrote extensively about the character and behavior of non-human animals in his Historia Animalium. One aspect of character is cognitive abilities. The chapter sets out Aristotle’s views on the cognitive abilities of animals, evidenced also in other works such as the Metaphysics and De Anima. All animals perceive but many also have imagination, memory, and practical intelligence. For Aristotle nonhuman animals have a sort of practical intelligence suited to their particular ways of life. The considerable overlap in cognitive abilities between human and nonhuman animals allows Aristotle to establish a biological basis for many human traits. Many nonhuman animals not only manage to organize their lives and negotiate new challenges but also maintain relationships with each other over extended periods. Social relationships require complex communication and involve a very important type of intelligence which is perfected in the most political of animals, human beings. The chapter ends with an account of how human cognition differs from that which occurs in other animals.

The chapter offers a brief discussion of Aristotle’s theory of animal self-motion and the conception of animal agency this theory implies. I start with a description of the philosophical problem Aristotle faces in accounting for animal self-motion. His solution to that problem, I argue, lies in a biological conception of the soul as the unmoved mover of the animal’s self-motions. His theory, I further argue, includes a biological account of desire as a process that may be described as a homeostatic mechanism of self-preservation on the level of perceivers. I then turn to the resulting conception of animal agency. Here I argue that Aristotle regards animals as self-movers insofar as they appropriate, and redirect, the energy they receive from the environment for their own purposes and in accordance with how they perceive things in the world. An Aristotelian account of the causation of an episode of animal self-motion will thus have to include reference to how things appear to the animal. I end the chapter with a brief discussion of the relation of Aristotle’s biological account of animal self-motion to his account of (rational) human self-motion.

Aristotle’s writings on animals comprise approximately a quarter of his surviving works. There are three lengthy treatises entitled Historia Animalium, On the Parts of Animals, and On the Generation of Animals. Other works on animals include On the Movement of Animals and On the Progression of Animals. In addition to these, a number of short discussions, collectively entitled the Parva Naturalia, focus on the capacities of living beings such as perception, breathing, and sleep. These works form what has been referred to by scholars in the last fifty years as the “biological corpus” of Aristotle. In them we find rich and varied discussions about anything from keenness of sight to egg laying, from parenting skills to dreaming. Much of the content of these works has been consistently marginalized in the history of philosophy.1 Bringing to light Aristotle’s biology as part of his philosophy is the main focus of this collection. This introduction will touch on the history, content, and methodology of these works and Aristotle’s key ideas on the science of living beings.

As the publication of this Cambridge Companion indicates, Aristotle’s biological inquiries are now accepted as an integral part of Aristotelian studies. The publication of Philosophical Issues in Aristotle’s Biology in 1987 is generally acknowledged to have been an important factor in bringing this change about. In this afterword, I briefly outline the events that led to that publication, and then describe, from a personal perspective, the remarkable growth of scholarly activity focused on Aristotle’s biology from 1987 up to the publication of the Cambridge Companion to Aristotle’s Biology.

The basis for terrestrial life in Aristotle’s biology is the nutritive process by which living things (plants and animals) produce and maintain their uniform parts and the organs made of these uniform parts. The nutritive process is thus extremely general, across all kinds. But it is also general in being present in all stages of the life cycle. Thus, it starts with the beginning of life, increases as the living thing grows, and subsides and is extinguished with the end of life. This variation in quantity is possible because there are two sides to the process, one is the heat necessary for “cooking” food into the parts of the living thing, and the other is the soul which informs this cooking. While the heat can be more or less, the soul is either there or not. The process of feeding (trephein) is shown to be Aristotle’s single sufficient and necessary condition for all natural life. It is the assimilation of food (trophê) to the living thing in question, an activity which the soul performs, thus producing and maintaining the living body, using the body’s heat as an instrument to work on food.

This chapter provides an overview of the theories of generation and hereditary resemblance found in Aristotle’s work On the Generation of Animals. This treatise completes the project of explaining the development of the perfected living being, which the epigenetic process of embryological development aims for. Aristotle’s explanation of how a new animal comes into being fits to his four-causal scheme, by adding in the more specific principles, male and female. The opponent, thinks Aristotle, is wrong to think that the generative contributions of the parents (seed, sperma) derive from all parts of the body. Instead, what male and female contribute is the most refined nourishment that their bodies produce, which is ready to become all the parts of the body. Male and female roles are then differentiated: the female provides this blood-derived product to serve as that material body (material cause) while the male’s seed is further refined so as to initiate and direct that development as the efficient cause. Aristotle also explains how it is that particular animals end up as male or female and come to resemble their blood relatives. The chapter ends by reflecting on Aristotle’s sexism in his theory of generation.

This chapter examines the reception of Aristotle’s biological work from his immediate successors to Roman intellectuals in the late Republic and early Empire. The Peripatetics, notably Theophrastus and Eudemus, endorsed many hallmarks of Aristotelian biology (e.g. classification by differentiae in Theophrastus’ Researches into Plants), and their works on animals focused mainly on areas that were relatively underexplored by Aristotle, such as animal behavior and “character.” Readers and users of Aristotle’s biological works outside philosophical circles were mainly interested in the wealth of facts collected in the Historia Animalium especially, and much less in Aristotle’s causal investigations. The main product of this scholarly engagement with Aristotle’s biology was the Epitome by Aristophanes of Byzantium, librarian at Alexandria around 200 BCE: it does aim to collect facts arranged by individual animals, but it also shows an interest in the main problems raised in GA. In Rome, Lucretius and Cicero were able to draw on Aristotelian biology to bolster arguments for Epicurean materialism and Stoic providentialism respectively. Finally, it is noteworthy that the now-lost Dissections played an important role in the early reception of Aristotle’s biology, at least until Apuleius in the second century CE.

The chapter sketches a broad picture of some ideas, antecedent to Aristotle’s work, about the origin and development of living beings. Against the background of the new cosmological and metaphysical framework of Aristotle’s biological enterprise, it emphasizes what distinguishes Aristotle from the Presocratics and Plato: his rejection of a shared causal story that would account for both the origin of the universe and the birth of animals and plants. This shift helps to make intelligible Aristotle’s rejection of hylozoism and of the opposite view that life arises, mysteriously, from inanimate material ingredients. To demonstrate that Aristotle discusses the biological views of his predecessors without directly using them to build his own theory, the chapter first turns to Presocratic fragments, mostly of Anaximander and Empedocles, which connect biological matters and cosmogony. Second, the chapter takes a fresh look at how Plato reshapes this connection in his Timaeus, offering a new account of the nature of the universe and the nature of human beings. This account then enables us to evaluate, in the chapter’s final section, the changes that Aristotle brings to the study of living beings, including his rejection of the notion of the latter’s progressive formation.

This chapter offers an overview of the reception of Aristotle’s biology in antiquity and beyond. It argues that Aristotle’s biology remained largely at the margins of the philosophical tradition even after the so-called return to Aristotle in the first century BC. The relative lack of engagement with Aristotle’s biological works reflects a change in the philosophical agenda. While Aristotle placed great emphasis on the philosophical dimension of his biology, his immediate successors considered biology an expendable part of their agenda. For a full appreciation of what Aristotle achieved in the field of biology, we have to go beyond antiquity. The reappropriation of Aristotle’s biological writings was a gradual process that began in the Arabic world and continued in the Latin world.

This chapter compares Aristotle’s theory of generation and Darwinian evolution by natural selection. It begins by explicating Aristotle’s distinction between intrinsic (kat’auta) and incidental (kata sumbêbêkos) final causation. Aristotle uses this distinction to differentiate Empedocles’ account of generation as incidentally final from his own intrinsically final view. Like Empedocles, Aristotle accepts spontaneous generation, but only as an exception to formal, sexual reproduction. In consequence, he describes spontaneous generation differently from Empedocles.

The chapter goes on to argue that by these standards Darwinian natural selection is intrinsically final and biologically (but not cosmologically) teleological. Accordingly, it is not nearly as similar to Empedocles’ primitive theory of “natural selection” as is sometimes assumed. That this difference was not apparent to Darwin’s contemporaries, or even to Darwin himself, is attributed to Darwinism’s subtle mixture of chance, determinism, and biological teleology. At first, the effects of medieval creationism on Aristotle’s hylomorphism and deterministic views about science were prominent factors standing in the way of understanding the logic of adaptive natural selection. Mid-twentieth-century Neo-Darwinism made the telic logic of Darwinian adaptation more perspicuous. Recent developments in regulatory genetics promise to give evolutionary meaning to something akin to Aristotle’s epigenetic account of generation.

Aristotle’s biological treatises are full of explicit commitments to empiricism, expressing both his own views about how one should conduct biological investigations while using observation and sharp critiques of his predecessors for failing to see the facts. This chapter examines some of the most prominent features of Aristotle’s commitments to empirical methods as they can be observed to be at work at the most basic level of his science of biology, that is, at the level of establishing the facts about the parts, activities, lives, and characters of animals as collected in his History of Animals (HA). Specifically, the chapter discusses Aristotle’s methods for establishing and evaluating facts as well as the sometimes all too important role played by folklore, fables, and hearsay in Aristotle’s collection of zoological facts.

In this chapter I introduce the thesis that Aristotle’s biology was considerably influenced by medical tradition as represented by the so-called Hippocratic writings. I start with a brief discussion of the history of the debate and the state of investigation and introduce the main advocates as well as opponents of the thesis. I then focus on Aristotle’s remarks on distinguished physicians and the relationship between medicine and natural philosophy in Parva Naturalia. With the help of selected passages from the Hippocratic On Regimen, On Flesh and On Ancient Medicine I make the case that Aristotle reflects upon a specific medical debate on the first principles of human (and animal) physiology and clarifies his own position in it, namely that he takes sides with those physicians who practice their discipline “in a more philosophical manner” and who employ heat, cold, and other such qualities as the starting points of their physiological explanations.

Parts of Animals Book 1 is mainly concerned with a discussion of the norms (horoi) that govern natural (biological) inquiry. In the present chapter I examine one of those norms, which concerns “how one ought to carry out an investigation of animals” (PA 1.1.639b3–5). Aristotle examines two alternative methods. The first recommends investigating animals species by species (e.g. sparrow, finch, raven). The second begins by grouping species into wider kinds (e.g. bird) and studies those features that belong to them as members of those wider kinds before going on to study those variations that differentiate one form of that kind from another (e.g. variations in beak shape). While scholars have been tempted to conclude that Aristotle rejects the first method outright, I argue that he thinks both approaches are important tools in the biologist’s tool-kit (PA 1.4.644b1–6). In the final section of the chapter I show how this discussion helps bring into focus the broader controversy surrounding the relation between the scientific theory presented in the Posterior Analytics and Aristotle’s scientific practice in the biological works.