I don’t like snakes. Sri Lanka, being a tropical country has a fair share of snakes that are both poisonous and non-poisonous and so I have encountered them, though not too many because I always lived in urban areas and snake sightings are rare, though not unheard of. But despite having encountered quite a few of them in the wild in my lifetime, I have never overcome my desire to get the hell as far away from them as possible.
Apparently there are good evolutionary reasons as to why humans and other animals fear snakes and why we have developed a heightened ability to see them over other things, almost before we are consciously aware that we are seeing them. It is because our brains and visual systems have evolved to be able to quickly detect them by developing specialized neurons for the purpose.
As this recent paper says:
The present study shows preferential activity of neurons in the medial and dorsolateral pulvinar to images of snakes. Pulvinar neurons responded faster and stronger to snake stimuli than to monkey faces, monkey hands, and geometric shapes, and were sensitive to unmodified and low-pass filtered images but not to high-pass filtered images. These results identify a neurobiological substrate for rapid detection of threatening visual stimuli in primates. Our findings are unique in providing neuroscientific evidence in support of the Snake Detection Theory, which posits that the threat of snakes strongly influenced the evolution of the primate brain. This finding may have great impact on our understanding of the evolution of primates.
Another article looks at the question of why some snakes are so venomous, much more so than would seem to be required. Some of the most dangerous specimens can be found in Australia which can boast of hosting the world record holder for the most venomous snake. This is the inland taipan that produces enough venom in a single bite to kill 250,000 lab mice.
Clearly this is overkill. So why did it evolve the reptile equivalent of a nuclear weapon while other snakes are not venomous at all ?
We do know that the common ancestor of all snakes possessed a rudimentary venom system. This means that all snakes had an equal evolutionary opportunity to become venomous. That not all snakes developed sophisticated venom delivery systems suggests that being highly venomous is not always the most efficient way for a snake to secure a meal.
There are no herbivorous snakes, but venom is not the only way that snakes can subdue their prey. Many snakes use constriction, as dramatically demonstrated in the recent battle between a python and crocodile in Queensland.
Some snakes simply rely on powerful jaws while others feed on defenceless prey such as eggs, so have no need of any additional deadly method of subjugation.
In nature, taipans need to kill their relatively dangerous rodent prey quickly, before it escapes or has a chance to retaliate. Living in a harsh, arid environment also means they must conserve resources, so they likely deliver only a tiny fraction of the contents of their glands each time they bite a prey animal.
The fact that this snake can kill 250,000 lab mice with a single dose of venom may also be due to the sheltered life that lab mice lead, which does not require them to have evolved to acquire venom resistance.