Leonardo da Vinci's anatomical studies, conducted through direct human dissection in an era when the practice was both scientifically primitive and often legally fraught, produced observations that stand up remarkably well against later discoveries. Around 1490, in notebooks now studied by historians of science as much as art historians, da Vinci turned his attention to the pineal gland — and described it as "the eye through which the soul regards itself."
Why that phrase is more than poetic
Da Vinci had no way of knowing, in any modern biochemical sense, that the pineal gland contains photoreceptor cells structurally similar to those in the retina. That discovery belongs to modern cellular biology, centuries later. And yet his instinct — to describe the gland in specifically ocular terms, as an eye rather than simply a gland — lines up with what would eventually be confirmed under a microscope.
Whether this was extraordinary intuition, extraordinarily careful anatomical observation, or some combination of both is a question historians of science still debate. What isn't in question is the historical record: the notebook entry exists, dated to approximately 1490, and its language anticipates a specific anatomical fact by roughly five hundred years.
Da Vinci's place in a longer pattern
Da Vinci is frequently cited alongside Nikola Tesla as a historical figure whose observations ran consistently ahead of the theoretical framework available in his own era — a pattern that recurs throughout the history of science, where careful individual observation sometimes outpaces the collective understanding needed to explain it.