Evolution: why try land? the eyes have it (Introduction)

by David Turell , Friday, September 15, 2017, 21:12 (2421 days ago) @ dhw

A whole new theory supported by optical measurements that much better vision on land encouraged terrestrial life:

https://www.quantamagazine.org/why-did-life-move-to-land-for-the-view-20170307/?utm_sou...

"Life on Earth began in the water. So when the first animals moved onto land, they had to trade their fins for limbs, and their gills for lungs, the better to adapt to their new terrestrial environment.

"A new study, out today, suggests that the shift to lungs and limbs doesn’t tell the full story of these creatures’ transformation. As they emerged from the sea, they gained something perhaps more precious than oxygenated air: information. In air, eyes can see much farther than they can under water. The increased visual range provided an “informational zip line” that alerted the ancient animals to bountiful food sources near the shore, according to Malcolm MacIver, a neuroscientist and engineer at Northwestern University.

"This zip line, MacIver maintains, drove the selection of rudimentary limbs, which allowed animals to make their first brief forays onto land. Furthermore, it may have had significant implications for the emergence of more advanced cognition and complex planning. “It’s hard to look past limbs and think that maybe information, which doesn’t fossilize well, is really what brought us onto land,” MacIver said.

"MacIver and Lars Schmitz, a paleontologist at the Claremont Colleges, have created mathematical models that explore how the increase in information available to air-dwelling creatures would have manifested itself, over the eons, in an increase in eye size. They describe the experimental evidence they have amassed to support what they call the “buena vista” hypothesis.

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"But once you take eyes out of the water and into air, a larger eye size leads to a proportionate increase in how far you can see.

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" They found that there was indeed a marked increase in eye size — a tripling, in fact — during the transitional period [to land]. The average eye socket size before transition was 13 millimeters, compared to 36 millimeters after. Furthermore, in those creatures that went from water to land and back to the water — like the Mexican cave fish Astyanax mexicanus — the mean orbit size shrank back to 14 millimeters, nearly the same as it had been before.

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"In water, a larger eye only increases the visual range from just over six meters to nearly seven meters. But increase the eye size in air, and the improvement in range goes from 200 meters to 600 meters.

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"MacIver’s background as a neuroscientist inevitably led him to ponder how all this might have influenced the behavior and cognition of tetrapods during the water-to-land transition. For instance, if you live and hunt in the water, your limited vision range — roughly one body length ahead — means you operate primarily in what MacIver terms the “reactive mode”: You have just a few milliseconds (equivalent to a few cycle times of a neuron in the brain) to react. “Everything is coming at you in a just-in-time fashion,” he said. “You can either eat or be eaten, and you’d better make that decision quickly.”

"But for a land-based animal, being able to see farther means you have much more time to assess the situation and strategize to choose the best course of action, whether you are predator or prey. According to MacIver, it’s likely the first land animals started out hunting for land-based prey reactively, but over time, those that could move beyond reactive mode and think strategically would have had a greater evolutionary advantage. “Now you need to contemplate multiple futures and quickly decide between them,” MacIver said. “That’s mental time travel, or prospective cognition, and it’s a really important feature of our own cognitive abilities.”

"That said, other senses also likely played a role in the development of more advanced cognition. “It’s extremely interesting, but I don’t think the ability to plan suddenly arose only with vision,” said Barbara Finlay, an evolutionary neuroscientist at Cornell University. As an example, she pointed to how salmon rely on olfactory pathways to migrate upstream.

"Hutchinson agrees that it would be useful to consider how the many sensory changes over that critical transition period fit together, rather than studying vision alone. For instance, “we know smell and taste were originally coupled in the aquatic environment and then became separated,” he said. “Whereas hearing changed a lot from the aquatic to the terrestrial environment with the evolution of a proper external ear and other features.'”

Comment: Fascinating theory. Raises the issue again of why pre-whales entered the water.