Tuesday, August 01, 2006

Eve's Lasting Legacy: The Serpent and The Apple

As per a recent scholarly article it seems that mammalian evolution may have been driven by the predatory presence of snakes. While some mammals adapted by becoming better snake sniffers, others developed immunities to serpent venom; while in the case of humans, the primates developed a good visual system to detect the snakes.

The other factor that drove human evolution (and hastened descent from the garden of eden after falling prey to serpent's designs :-) ) was the fact that anthropoid ate fruits (substitute apples :-) ) and this frugivorus eating habit endowed them with enough-glucose-availability-in-the-brain to act as a pre-adaptation necessary to the evolution of brain matter required for visual acuity needed to detect snakes and take appropriate action.

Fox news has an excellent article on the same which is a needed reading before one can try to appreciate the excellent coverage of the same done by John Hawks.

I'll try to summarize the arguments.

1. It is common knowledge that runaway arms-race between predators and preys lead to selective development of traits in a particular direction. For eg, the great cats and the antelopes, both developed systems for high speed chase and run-away and thus some of the fastest runners are either predators; like leopards or preys like the antelopes. What food (and energy one gets from it) also ensures who outnumbers whom in the arms race (the tiger wins!). The responses may not be symmetric, while Great Cats may develop claws and teethes, the antelope may develop antler ( though antler evolved more as species specific displays to attract opposite sex).

2. Snakes are one of the predatory species for mammals. Earlier snakes relied on Boa constriction method to kill the preys, but evolved venom about 60 mn years ago as their second weapon. Mammals reacted by either detecting them (in close range) by sniffing, or developing venom resistance etc.

3. Primates leading to Humans reacted by detecting motion (via MT and other motion detecting brain areas), color and other relevant visual stimuli to predict and detect the snake's presence at close ranges and take appropriate areas.

4. The increased encephalisation (dependent on processing of more visual stimulus and reacting to it) was dependent on a previous adaptation related to fruit eating and abundant availability of glucose in brain.

5. The features of human vision like orbital convergence (leading to depth perception and 3D vision) are tuned for such snake -detection mechanisms.

6. The koniocellular pathway is crucially involved (among other tasks) in pre-attentional visual detection of fearful stimuli, including snakes and the evolution of this system points to snake-primate arms race pressures and how the primates adapted.

7. The Parvocellular pathway is also implicated in the study (as details and color are important for snake detection). Although the magnocellular is not , but I believe movement is also very crucial as snakes have a typical motion.

Lastly, while the analogy of the snake and the apple is quite relevant in the Christian mythology context, the snake is a revered creature in many mythologies (dragon in Chinese for example) and we in India celebrated Naag Panchami - a day when snakes are fed milk- a couple of days back.

Some parting notes:

1. In experiments with monkeys and humans it has become apparent that we have specialized fear associations for snakes. For example a young monkey, which sees another monkey as reacting in a frightened manner to say a plastic snake, would by even a singular exposure to such a display of fear, clear to have fearful associations with say the plastic snake. This association can be even when the observed behavior is seen on TV (and is recorded and not happening in real-time) Like the disgust reactions and avoidance-of-just-before-taken-food in response to a single vomit, it seems the avoidance learning for snakes is also built-in and can be triggered even by one exposure and by observational learning. Thus, there is strong evidence that we have specialized circuits for responding to snakes. It makes merit to assume that we should have for detecting too.

2. In Indian philosophy, one perennial question, focused on differentiating reality from illusion is differentiating snake for the rope. the rope in dark gives illusion of a snake, but we need to enhance our perceptions and awareness to realize that the fear of the snake is illusory and that the feared object is only a rope. This example, which is in ancient texts, is evidence of the importance of snake detection from prehistoric times.

Endgame: Can one identify from which book this drawing of boa constrictor and elephant is inspired?

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5 comments:

Archana Bahuguna said...

Amazing pic! where did you get that from :-)?

Sandy G said...

Hmm....Let me think... Maybe it was a sketch from Da Vince and has some code embedded in it...Maybe it is a contemporary Hussain sketch with Hussain saturated with his panchant for horses and shifting attention to elephents and boa-constrictors. ...I dont remember well...all I know is that it is from some relally great artist. On second thoughts, maybe its by you:-)

QuasiPfred said...

The drawing comes from the Little Prince. The narrator explains how, as a child, his first drawing was of a snake after eating an elephant. He was even careful to include the eye on one side, but every adult he showed it to thought he had drawn a hat. His second drawing tried to show the elephant inside the snake, but it was still not appreciated by any adult who was shown the picture. When the narrator finally meets the Little Prince, who insists on having a picture drawn, he draws the first picture, and is shocked to hear the little prince say he does not want a snake after having eaten an elephant. I love going back to that story, as a reminder that adults and children see things -- everything -- very differently.

Sandy G said...

Hi Quasipfred,

Welcome aboard! and yes, you are right, this is an artwork inspired from The Little Prince by Saint
Exupery anmd created by my dear friend Archana.

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