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Skip to 0 minutes and 7 secondsAs we've seen last time, according to thinkers such as Descartes and Boyle, bodies are complex structures that result from the motion and collision of particles. As in the case of clocks and watches, their physical characteristics result from the inner arrangement of their material parts. According to many, this provided a much more intelligible and less anthropomorphic account of natural bodies than scholastic Aristotelianism had. Yet the new model was not without puzzles of its own. To see this, consider the difference between a relatively simple structure like a stone or mineral, and the much more complex structure of a living organism like a chicken. Perhaps the stone or mineral is the result of the motion and collision of particles.

Skip to 0 minutes and 45 secondsBut does the same story work just as well in the case of the formation of the chicken? According to many, organic structures were just way too complex to be the result of the mere law-guided motion of particles. Even if the motion and collision of particles could result in an organic structure once, that the same, highly fine-grained and complex organic structure should result time and again from the law-guided motion of particles-- that, to many, seemed unbelievable. To see this, a comparison might help. Suppose, then, that we take a number of plastic letters, and that we drop them on the floor.

Skip to 1 minute and 22 secondsNow, it's already quite hard to imagine how, from the motion of these letters as guided by gravity and the laws of motion, a Shakespeare sonnet would result even once. But that the same Shakespeare sonnet would result time and again as we repeat the experiment-- that seems truly unbelievable. The case of animal generation, then, presented this special difficulty for a mechanisation of nature. So how did scientists and philosophers deal with this difficulty? Here, we roughly find two strategies. The first is to harken back to the toolkit of Aristotelian natural philosophy. Thus, according to the English biologist William Harvey, when a chicken develops in an egg, this process is guided by what he called a "formative power."

Skip to 2 minutes and 0 secondsThis formative power organised the material of the egg in such a way that eventually, the structure of the chicken would emerge. Now, the details of this process needn't concern us here. But the salient point for now is that in this account, matter is not quite passive. At least in the case of animal generation, it displays a capacity for self-organization that seems much better at home in Aristotelian natural philosophy than in a strictly mechanistic worldview. The second strategy was to think of animal generation along the lines of what we may call a Russian doll model. Just as each Russian doll contains a miniature version of itself on this account, each parent contains a miniature version of itself.

Skip to 2 minutes and 38 secondsNow, the proponents of this view were split over the question of whether this miniature was contained in a maternal egg, or rather in a paternal seed. According to Descartes' follower, Nicolas Malebranche, for instance, the offspring of an animal was contained in the maternal egg. And the first generation of each animal species, or kind, in this view, was created by God as, you might say, the ultimate Russian doll, in which all future generations were already contained. This preformationism, as the theory is officially called, might sound bizarre to you. And indeed, it does have a poor reputation among many historians and scientists. Even so, it's important to realise that it emerged as an answer to a genuine difficulty in the 17th century.

Skip to 3 minutes and 17 secondsIt emerged as a way out of the difficulty of how complex organic structures could possibly result from the mere motion and collision of particles. According to some, indeed, the case of animal generation laid bare some of the limits of the mechanisation of nature, and preformationism was historically important as one way of dealing with those limits.

Biology and the limits of mechanisation

Many of the scientists and philosophers of the seventeenth century found it hard to see how animals could be generated from the mere sticking together of particles as guided by the laws of motion. Perhaps stones could be formed in this way, but organic structures were just way too complex to result from the mechanical interplay of minute parts of matter.

In this video, we see how thinkers such as the English biologist, William Harvey (1578-1657), and the French philosopher, Nicolas Malebranche (1638-1715), dealt with this problem. As we will see, Harvey in his account of animal generation harkened back to the toolkit of Aristotelian natural philosophy. Malebranche, on the contrary, argued that God had created the first female member of each animal species as a kind of Russian doll, in which miniature versions of all future generation were already somehow contained.

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The Scientific Revolution: Understanding the Roots of Modern Science

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