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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Aristotle's biology | 3/6 | https://en.wikipedia.org/wiki/Aristotle's_biology | reference | science, encyclopedia | 2026-05-05T16:11:59.770600+00:00 | kb-cron |
The child's sex can be influenced by factors that affect temperature, including the weather, the wind direction, diet, and the father's age. Features other than sex also depend on whether the semen overpowers the menses, so if a man has strong semen, he will have sons who resemble him, while if the semen is weak, he will have daughters who resemble their mother.
==== Embryogenesis ====
Aristotle's model of embryogenesis sought to explain how the inherited parental characteristics cause the formation and development of an embryo. The system worked as follows. First, the father's semen curdles the mother's menses, which Aristotle compares with how rennet (an enzyme from a cow's stomach) curdles milk in cheesemaking. This forms the embryo; it is then developed by the action of the pneuma (literally, breath or spirit) in the semen. The pneuma first makes the heart appear; this is vital, as the heart nourishes all other organs. Aristotle observed that the heart is the first organ seen to be active (beating) in a hen's egg. The pneuma then makes the other organs develop. Aristotle asserts in his Physics that according to Empedocles, order "spontaneously" appears in the developing embryo. In The Parts of Animals, he argues that what he describes as a theory of Empedocles, that the vertebral column is divided into vertebrae because, as it happens, the embryo twists about and snaps the column into pieces, is wrong. Aristotle argues instead that the process has a predefined goal: that the "seed" that develops into the embryo began with an inbuilt "potential" to become specific body parts, such as vertebrae. Further, each sort of animal gives rise to animals of its own kind: humans only have human babies.
== Method ==
Aristotle has been called unscientific by philosophers from Francis Bacon onwards for at least two reasons: his scientific style, and his use of explanation. His explanations are in turn made cryptic by his complicated system of causes. However, these charges need to be considered in the light of what was known in his own time. His systematic gathering of data, too, is obscured by the lack of modern methods of presentation, such as tables of data: for example, the whole of History of Animals Book VI is taken up with a list of observations of the life histories of birds that "would now be summarized in a single table in Nature – and in the Online Supplementary Information at that".
=== Scientific style ===
Aristotle did not do experiments in the modern sense. He used the ancient Greek term pepeiramenoi to mean observations, or at most investigative procedures, such as (in Generation of Animals) finding a fertilised hen's egg of a suitable stage and opening it so as to be able to see the embryo's heart inside. Instead, he practised a different style of science: systematically gathering data, discovering patterns common to whole groups of animals, and inferring possible causal explanations from these. This style is common in modern biology when large amounts of data become available in a new field, such as genomics. It does not result in the same certainty as experimental science, but it sets out testable hypotheses and constructs a narrative explanation of what is observed. In this sense, Aristotle's biology is scientific. From the data he collected and documented, Aristotle inferred quite a number of rules relating the life-history features of the live-bearing tetrapods (terrestrial placental mammals) that he studied. Among these correct predictions are the following. Brood size decreases with (adult) body mass, so that an elephant has fewer young (usually just one) per brood than a mouse. Lifespan increases with gestation period, and also with body mass, so that elephants live longer than mice, have a longer period of gestation, and are heavier. As a final example, fecundity decreases with lifespan, so long-lived kinds like elephants have fewer young in total than short-lived kinds like mice.
=== Mechanism and analogy ===
Aristotle's use of explanation has been considered "fundamentally unscientific". The French playwright Molière's 1673 play The Imaginary Invalid portrays the quack Aristotelian doctor Argan blandly explaining that opium causes sleep by virtue of its dormitive [sleep-making] principle, its virtus dormitiva. Argan's explanation is at best empty (devoid of mechanism), at worst vitalist. But the real Aristotle did provide biological mechanisms, in the form of the five processes of metabolism, temperature regulation, information processing, embryonic development, and inheritance that he developed. Further, he provided mechanical, non-vitalist analogies for these theories, mentioning bellows, toy carts, the movement of water through porous pots, and even automatic puppets.
=== Complex causality ===
Readers of Aristotle have found the four causes that he uses in his biological explanations opaque, something not helped by many centuries of confused exegesis. For a biological system, these are however straightforward enough. The material cause is simply what a system is constructed from. The goal (final cause) and formal cause are what something is for, its function: to a modern biologist, such teleology describes adaptation under the pressure of natural selection. The efficient cause is how a system develops and moves: to a modern biologist, those are explained by developmental biology and physiology. Biologists continue to offer explanations of these same kinds.
=== Empirical research ===