Humans Descended From One-Eyed Ancestors, Study Finds

The human eye, a marvel of evolution, shares a surprising evolutionary link with the single-eyed Cyclops of Greek mythology. New research suggests that the distant ancestors of vertebrates, the group that includes humans, were creatures with a single eye in the center of their heads.

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The eyes of humans (vertebrates) and octopuses (invertebrates) have different origins.

This discovery challenges the common understanding of how eyes evolved. While many invertebrates, like the octopus, possess paired eyes and a central light-sensing organ, vertebrates' evolutionary path diverged. Early bilateral animals had this paired-eye structure, a trait that persisted in invertebrates. However, the ancestors of vertebrates, which lived in the deep sea, found vision less critical. Their paired eyes degenerated, leaving only the central light-sensing organ, making them 'one-eyed' beings.

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Early bilateral animals had paired eyes and a central light-sensing organ. This structure is passed down to invertebrates today.

Over time, as these ancestors adapted to different environments, some lineages re-evolved the need for vision. The central light-sensing organ differentiated into a proto-pineal and proto-retina. To gain depth perception, these structures migrated to the sides of the head, eventually developing into the sophisticated paired eyes we recognize today. The pineal gland, responsible for melatonin production and regulating circadian rhythms, remains as a vestigial light-sensing organ in many vertebrates, a reminder of our one-eyed past.

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Vertebrates evolved from ancestors with a single eye, later developing paired eyes for better depth perception.