Humans: the world's only super predator?

Everyone is familiar with how predators and prey interact with each other - predators try to eat prey species and prey species, which do not want to be eaten, fight back or run away. These interactions have led to an 'evolutionary arms race' between predators and prey: where predators evolve adaptations, such as weapons, to help them kill their prey; and their prey evolve defences to counteract these weapons.

A good example of this is the cheetah, which has evolved to be able to run extremely quickly in order to catch gazelle, their main source of prey. Gazelle have worked out that they cannot outrun cheetahs, which are the fastest land-animal, so instead have evolved to be able to abruptly change direction whilst running. This allows them to be able to twist and turn even when sprinting and helps to protect them from cheetahs, which can only run in near enough straight lines. Furthermore, cheetahs are under a great deal of strain whilst running and their core body temperature rises extremely quickly so they cannot run for long periods of time. Consequently, gazelle have also evolved to be good long-distance runners, with most of their muscles being made from fast oxidatve fibres, which allows them to run for much longer than cheetahs can. As the next step in the evolutionary arms race it may be predicted that cheetahs will evolve to be able to run for longer or develop greater manoeuvrability whilst running, allowing them to be able to hunt gazelle more efficiently.



A cheetah chasing a juvenile gazelle. The cat can reach speeds of up to 75mph during the chase and will try to knock the gazelle over, allowing it to grab the underside of the gazelle's throat and suffocate it.

Arms races such as this example are common and exist in some form or another for every species of predator and prey. This is expected by scientists and obviously, makes evolutionary sense. What does not make sense however is that although humans have been around for 2 million years, in which time we have hunted other animals extensively, we do not appear to be engaged in this arms race. We have evolved no specialised weaponry to hunt our prey and none of the species that we prey upon have evolved abilities to defend themselves against us.

Many scientists believe that this is due to the unique way in which we hunt our prey. As I'm sure you know, humans are extremely intelligent and we have always used this intelligence to help us hunt other animals. Our brains have allowed us to create a large variety of tools to overcome our lack of physical weaponry and to develop innovative tactics to overcome our prey's defences.

One such ability of ability of humans is that we are able to throw much more efficiently than any other living animals - both in terms of power and accuracy. Therefore once our ancestors had invented spears, the once cutting-edge technology, we were able to kill our prey from a distance by throwing it - the ability to kill from a distance is unique to us, no other animal is able to do this! Our ability to kill animals from a distance meant that we have had no need to develop weapons such as poisons, claws and large teeth and our prey has not had the opportunity to develop resistance to such a hunting method. This is partly because once an animal had realised that we could kill it, it is already dead and cannot pass its genes on, which is the mechanism by which evolution works. Our intelligence has also meant that we could fashion dull clothing and refine our tactics to sneak up on our prey, so that we have not needed to evolve camouflaged skin either. In fact, the main physical adaptations that throwing would have selected for is strong shoulder and leg muscles and good binocular vision (predators have eyes that are mounted on the front of their head, which gives more precise vision and better depth perception), both of which humans have.

Tribesmen throwing spears. Note how the men are standing sideways, holding the spear in their right arms. When they throw their spear they twist their body around. This greatly increase the force of the throw by using the torque generated in their hips and shoulders.

Human intelligence and the fact that we hunted in packs has also meant that we were able to overcome the  'ten times larger' rule, which is where large terrestrial herbivores that grow ten times heavier than their largest predator become safe from predation, since their predators are unable to develop jaws strong enough to kill them. This explains the large size of elephants for example, and why the adult individuals of such species have no natural predators other than man - simply put, they are just too large for predators for hunt and the risk of injury to the predator is too high! Our ability to hunt animals much larger than ourselves helped the rapid spread of humans across the globe and allowed us to live in areas that would have otherwise been uninhabitable, such as the cold tundra of Northern Europe and Siberia. Human colonisation of tundra climates was possible due to the presence of mammoths, a species of megafauna, for two main reasons. Firstly, mammoths had no natural predators until we arrived, so that we did not need to complete for them with other predators; and secondly, because of the enormous amount of resources than we could harvest from each individual. These resources included meat for food, fur for clothing and vitreous humour from their eyes to make glue. Unfortunately mammoths, like most species of megafauna, had evolved with immunity to their natural predators and consequently, had few defences other than their size. This meant that we were able to kill them very easily and sadly, we drove them to extinction. The extinction of megafauna is a characteristic of human colonisation in new areas and most giant species became extinct around 40 million years ago.

An artist's impression of a group of early humans hunting a mammoth.

Our ingenuity has also meant that humans have been able to overcome most of the poisons that many animals use as defence mechanisms. The most common ways that we do this is by cooking the animal before we eat it, which causes the poisons to break down; or we can remove the poisonous tissues, which is possible because defensive poisons are often concentrated into certain organs, such as the liver. Thus, humans can kill and eat many animals that are avoided by other predators.

Therefore humans are remarkable hunters, being the only animals that can kill others from a distance, kill species much bigger than ourselves and can remove poisonous toxins from our food, which greatly increases the scope of our diet. Thus, it may be fair to say that humans are not merely predators, but are in fact super predators and that we are the most effective and efficient killers that have ever lived.