Examining in more detail how one prominent seventeenth-century scientist treated animals, both on a philosophical and a practical level, can give a sense of the intricacies of contemporaneous views of animals. The Dutch scientist Christiaan Huygens is known for his invention of the pendulum clock, founding of the wave theory of light, and discovery of the true shape of the rings of Saturn, to name only a few of his prolific activities. Yet he does not figure among the prominent anatomical and medical inquirers of the Scientific Revolution. His consideration of animals, however, was quite intriguing and demonstrates in detail the increasing early modern tension between recognition of animal sentience, on the one hand, and the incentive to utilize animals, and the natural world in general, on the other.

Toward the end of his life, Huygens worked on his last important work, eventually published posthumously in 1698 and usually referred to as the Cosmotheoros. In this work he made some short claims on animals which were distinctly opposed to the Cartesian beast-machine theory with its claim for the lack of sentience in animals. According to Huygens, some animals displayed varying levels of rationality. Dogs, apes, beavers, elephants, and some birds and bees, had “somewhat in them of Reason independent on, and prior to all teaching and practice.” Therefore human beings were not the only rational animals. “But still no Body can doubt, but that the Understanding and Reason of Man is to be prefer’d to theirs [the animals’] as being comprehensive of innumerable things, indued with an infinite memory of what's past, and capable of providing against what's to come.” In what related to things such as self-preservation, education, and providing for themselves and their offspring, animals performed most of these things with greater facility than human beings. The latter's sense of virtue, justice, friendship, gratitude, and honesty were meant to put a stop to their own wickedness, or to provide security against mutual assaults and injuries, things in which animals “want no Guide but Nature and Inclination.” Therefore, if one compared the many cares, disturbances of mind, restless desires, and dread of death, which resulted from human reason with “that easy, quiet, and harmless Life” which animals enjoyed, then one was “apt to wish a change.”