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Tarsiers

Look at the picture below from the website of Cleveland museum of Natural History.

Source: Website of Cleveland museum of Natural History

Do you realize what it is? And what they are? You realize what “they” refers to, don’t you? I am referring to the two gaping holes. My wife was reminded of vessels.

It is a skull and the positioning of the holes is a giveaway. Those are indeed eyes. Can you imagine what a creature like that would look like? Here it is. Given below is a picture of the animal from Wikipedia.

Tarsier - Source: Wikipedia

They are Tarsiers. What makes them so endearing is the size of their eyes.  Though I have seen their pictures before, what brought them back to my attention is the book I am reading:  “The ancestor’s tale” by Richard Dawkins.

Tarsiers are nocturnal, which is, they are active at night. That explains their large eyes, since during the night, there is very little light, and hence they want to take in as much of it as possible.

The reason why many organisms were driven to a nightly lifestyle, is because at one stage, dinosaurs dominated the earth, and not many animals could be active in the day, unless they wanted to become a prey of the Dinosaurs. Hence many chose a nocturnal lifestyle. Of course, once Dinosaurs became extinct, the opportunity was quickly exploited by many animals by re-occupying the day time niches.

But there is another fact that Dawkins explains about the eyes of Tarsiers. If big eyes are so beneficial at night, why dont many animals have large eyes. That is because other animals have a simple but beautiful innovation, which helps them manage with small eyes. When you shine a torch at the eyes of some animals like the cat, you can see them really bright at night. Given below is a picture of an aye-aye, a close relative of the Tarsiers, taken at night showing its bright eyes.

Aye-aye - A picture from wikipedia. (Picture by Tom_Junek)

That is because, some animals have a reflective surface just behind the retina. The purpose of this reflector, called Tapetum Lucidum, is that at night, when the very little light available passes through the retina, hits the reflector, which forces it to turn back and pass through the retina again. This provides the retina two opportunities to sense the same light, thereby improving their vision.

But the Tarsiers, for some reason, have not evolved this, but instead, chose the strategy of bigger eyes. That is how evolution works. Any strategy, as long as it works, will do.

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