Descartes considered animals to be little better than automata and given his high social position and intellectual achievements, and the convenience of this argument for his co-religionists, it stuck. Even today (and right here on HN), any sort of conjecture on the inner life of animals tends to bring out a few finger-waggers condemning 'athropmorphism.'

https://philosophynow.org/issues/108/Descartes_versus_Cudwor...