A cobra is any of several species of highly venomous snakes, the majority of which stretch the neck ribs to form a hood. While the hood is a common feature of cobras, not all are linked. Cobras can be found in Southern Africa to the islands of Southeast Asia. Throughout their range, many species are favorites of snake charmers, who scare them into adopting the upreared defense posture. But did you know how spitting cobras became what they are today?
Spitting Cobras first appeared in the fossil record around the time of early humans. It is believed that these snakes spray venom in response to the physical pressure applied on them by humans when they were used as projectile weapons.
Could this Evolution have been Triggered by our Ancestors?
Venom spitting is a rare behavior observed only in a few closely related snake species. Nonetheless, this projectile defense system and the exact combination of poisons that causes more agony evolved three times separately within this tiny population.
This type of defense must have been triggered by intense selection pressure. Several variables, we believe, make human predecessors the most likely selected agent.
Many primates may kill a snake if they feel threatened, frequently utilizing projectile weapons or tools such as pebbles and sticks. While these are not usually lethal, they can cause significant damage. Bipedal hominins, which walked on two legs with their forelimbs freed, posed a bigger long-distance threat than their four-legged relatives. This necessitates a long-distance defense from their serpentine foes, such as spitting.
The evolution of venom spitting corresponds to important dates in the history of early human ancestors. Spitting first appeared in African cobras some 7 million years ago, around the same time as hominins separated from the ape and bonobo lineages. Spitting evolved in Asian cobras roughly 2.5 million years ago, concurrent with the emergence of Homo erectus in Asia. (Source: The Conversation)
Unique Toxin Cocktails
Snake venoms are complex protein combinations largely used in foraging to incapacitate prey effectively. While snakes deploy their venom in self-defense, as in the case of human snakebites, most evidence suggests that venom composition developed for foraging rather than defense.
The venom of fixed front-fanged snakes, such as cobras, causes paralysis. This is due to an excess of neurotoxic three-finger toxins, which block neurotransmission or impulses sent from the neurological system to the muscles of the prey. On the other hand, Cobras contain three-finger poisons that damage cells rather than impede neurotransmission. These are known as cytotoxins.
The results indicate that spitting cobras have a higher abundance of a distinct toxin family termed phospholipase A2 (PLA2s) in their venom than non-spitting cobras. Because these cobras spit for defense, this is the first indication of a defensive driver of snake venom evolution. (Source: The Conversation)
How Far Can a Spitting Cobra Spit?
These snakes provide a two-pronged threat. They can not only inject venom through a painful bite, but they can also spit their toxins two or three yards out. When they want to, they can move very swiftly. (Source: Natural History Museum)
Image from Science.Org