Study ties vertebrate eyes to 600‑M‑old worm ancestor
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- Researchers surveyed 36 major groups of living bilateral animals and found eyes and light‑sensing cells consistently located either on both sides of the face or at the head midline.
- Worm‑like ancestor living 600 million years ago lost its paired steering eyes when it became a stationary filter feeder, retaining only the midline light‑sensing cells.
- Midline eye evolved into a small eye that later gave rise to the pineal organ, which in many vertebrates still receives light and regulates melatonin.
- Paired eyes reappeared after the ancestor returned to swimming, forming eye cups that moved to the sides of the head and became the modern vertebrate eyes.
- Invertebrates such as insects, crustaceans, octopuses, and snails retain the original paired light‑sensing cells, with compound or camera‑type eyes, but have far fewer retinal neuron types than vertebrates.
- Mammalian pineal organ lost its light‑sensing capacity, shifting light detection to the eyes for melatonin regulation.
Why it matters: The findings give evolutionary biologists a concrete ancestral model linking retinal complexity to early midline light‑sensing structures, prompting a reassessment of how vertebrate visual and circadian systems co‑evolved; neuroscientists gain a new framework for exploring retina‑brain wiring, while the broader scientific community benefits from a clarified evolutionary narrative.
