Evolution: primate vision same for 55 million years (Evolution)

by David Turell , Friday, December 04, 2020, 16:03 (1238 days ago) @ dhw

From the tiny mouse lemur to us, the visual system is the same in size in the brains of all:

https://www.sciencedaily.com/releases/2020/12/201203144156.htm

"Primates process visual information similar to pixels in a digital camera, using small computing units located in their visual cortex. Scientists of the University of Geneva have investigated whether these computational units scale across the large differences in size between primates. The gray mouse lemur is one of the smallest of them and his visual processing units reveals that all primates, independent of their body size, have an equivalent computational units.

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"The gray mouse lemur (Microcebus murinus) from Madagascar is one of the smallest of them and weighs barely 60 grams. In a study published in the journal Current Biology, the scientists compared the visual system of the mouse lemur to that of other primates and found that the size of these visual processing units is identical in all primates, independent of their body size. As the mouse lemur is a very special species, sharing many traits with the very first primates that evolved 55 Million years ago, these results suggest an incredible preservation of our visual system and highlight the importance of vision in our daily lives and that of our ancestors in the distant past.

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"The team made a surprising discovery: not only was the basic processing unit almost identical in size in the 60-gram mouse lemur, as in larger monkeys such as macaques weighing about seven kilograms, or even larger primates such as us humans.

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"They also found that the way the units are arranged across the brain was totally indistinguishable, following the same rules with mathematical precision. The researchers also found that the number of nerve cells per visual unit was almost identical in all primates studied so far. Göttingen Max Planck physicist Fred Wolf who had pointed out that universal mathematical principles may rule visual system evolution ten years ago is still amazed by the degree of invariance: "55 Million years of separation on different continents is a very long evolutionary path to travel. I would have expected some mix of general similarity and characteristic differences between species in these neural modules. But the fact of the matter simply is: It is practically impossible to tell them apart." (my bold)

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"...the discovery by UNIGE scientists and their collaborators reveals that this part of the visual system cannot be compressed or miniaturized. A fixed number of neurons seems therefore to be required to ensure its optimal functionality. "For tiny primate species with excellent vision, such as the mouse lemur, the visual system must hence be relatively large, compared to the size of their entire brain, to accommodate a sufficient number of visual processing units," says the Geneva-based neuroscientist. Indeed, more than a fifth of the cerebral cortex of this lemur is dedicated to visual processing. In comparison, the neural circuits related to vision occupy barely 3% of the human brain."

Comment: Note the bold. A perfect system with no changes and the surprise of a researcher noted in bold. No changing mutations implies controlled design.