Our eyes are 500m years old
Our eyes are at least half a billion years old, a good deal older than the brain - a new study has found. The eyes are one of our most remarkable and precious organs, yet their origins have been shrouded in mystery until quite recently, said Professor Trevor Lamb of the Australian National University and The Vision Centre.
The deep origins of “sight” go back more than 700 million years when the Earth was inhabited only by single-celled amoeba-like animals, algae, corals and bacteria.
At this time the first light-sensitive chemicals, known as opsins, made their appearance and were used in rudimentary ways by some organisms to sense day from night. Ancient cells already had signalling cascades that sensed chemicals in their environment, and the advent of opsins allowed them to sense light. “But these animals were tiny, and had no nervous system to process signals from their light sensors,” he said. Over the following 200 million years those simple light-sensitive cells and their opsins slowly and progressively became better at detecting light, they became more sensitive, faster, and more reliable, until around 500 million years ago they already closely resembled the cone cells of our present day eyes.
“The first true eyes, consisting of clumps of light-sensing cells, only start to show up in the Cambrian, about 500 million years ago, and represent a huge leap in the evolutionary arms race,” Lamb said.
“Our type of eye, a single globe packing in millions of photoreceptors, first starts to emerge between 500-600 million years ago. This was the crucial moment for our vision system,” Lamb said in a recently published scientific review in ScienceDirect. “Baby sea squirts have a simple eyespot called an ocellus, which is basically a bundle of photoreceptors. The adult animal loses this, as it becomes immobile, so vision is not important. This organ appears to date back at least 600 million years.
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