As a ranger, we have the opportunity to show guests from all over the world animals that they may have never seen before. Having grown up seeing these animals frequently one often just accepts it for what it is and you don’t necessarily ask yourself how or why. This is precisely what happened a few days back when a guest asked me,
“Why did elephants evolve to have trunks?”
So I decided to dig a little deeper into the evolution of the African elephant.
Evolution and History
Proboscidea is a taxonomic order with one living family, Elephantidae, and several extinct families. Three species of elephants are currently recognised: the African savanna elephant, the African forest elephant and the Asian elephant. Here at Londolozi, we see the African savanna elephant and so this is the species I will focus on albeit the evolutionary history is largely shared across these three species.
Proboscideans were a diverse and widespread group of herbivores that first appeared in Africa about 60 million years ago. Not all of the elephant’s close relatives were as big as the elephants we see today. In fact, some of the earlier species, such as the Eritherium which lived in Morocco, were as small as foxes and lacked a trunk. But with the separation of landmass resulting in drastic shifts in climate for this order of mammals, some species evolved to be far greater in size. The elephants we see today came from a prehistoric elephant known as Gomphotherium about 20 million years ago.
Essentially all animals are trying to survive and procreate. By Darwin’s theory of evolution and natural selection, the species best suited to their environment are the most successful at reproducing and passing on their traits from generation to generation. So why did elephants get so big?
We can only theorise this answer but if you’ve ever watched an elephant feed off the tops of trees or push a tree over with little effort it is clear that it is a survival advantage. They can feed on many different areas of a tree that other animals either can’t reach or can’t gain access to. This survival advantage of size goes further in the sense that they can defend themselves, store fats and water better, digest more efficiently and develop larger brains. The cost of growing to the size they have is the amount of food they need to ingest to fuel such a massive body.
When one looks at an elephant it is easy to assume that they are fat animals but in fact, this is very far from the truth. Inside the belly of an elephant is a vast digestive system that uses up every last inch of space. Not being ruminants they require a lot more bulk to extract the nutrients they require to survive from day to day. Over 20 days, they will consume the equivalent of their body weight. Only about 40% of this is actually digested.
One of the most critical parts of their digestive system is the caecum. It is a large sack that sits between the small and large intestines and is where a large part of the fermentation of the plant matter they eat happens. Both the large and small intestines are both extremely long to give the elephant the best chance of getting enough nutrients into the bloodstream. This is also improved by the ability of the elephant to grind its food down as much as possible in its jaw before actually swallowing.
To cope with so much fibrous food the mouth of an elephant has evolved extraordinarily. The massive muscles of the jaw, which are continuously chewing for almost 20 hours of the day, generate a lot of heat. Within this powerful jaw is a pretty impressive set of teeth. The six sets of molars that an elephant will work through in its lifetime don’t all grow at once. Along the surface of each molar are several ridges. Each ridge is called a lamella and as the elephant grows a new lamella is produced from the back of the jaw that attaches to the one in front of it. These lamellae are constantly growing and replacing ones at the front of the jaw that are ground down through excessive use. It’s as if they have a conveyor belt of teeth constantly replacing old ones.
But to get food into their mouths from such a height off the ground they have an even more impressive evolutionary adaptation, the trunk
The trunk of an elephant is literally one of a kind. It is an incredibly versatile organ that is used for social greetings, drinking, feeding, and breathing. Unlike most other limbs of a mammal, there is no bone within it. There are thousands upon thousands of muscles arranged in all different directions giving the elephant full control in moving it in all different directions. To put it in perspective a human’s body has around 600 muscles in total yet an elephant has 40 000 just in its trunk! No wonder elephant calves take almost 2 years to get full control of their trunks. But what was the selection pressure or advantage of having such a long trunk?
One theory is that it enabled the elephant to be able to reach the water without having to lower its head the way a giraffe does. As mentioned before, simply the advantage of reaching the tops of trees which most other animals are not able to reach is a clear advantage in its own right. Palaeontologists, however, having studied millennia of Proboscidae fossils believe that the trunk may have evolved as a snorkel. Having observed elephants playing in the water and even swimming across deep rivers with nothing but their trunk sticking out of the water makes me think that perhaps this isn’t too far from the truth. But simply having a long trunk isn’t enough to be able to breathe while submerged in water.
Not only is the trunk unique to the elephant but the way their lungs have adapted is so too. With their growth in size their lungs needed to become supercharged to provide them with an adequate oxygen supply. However, the uniqueness of these massive lungs lies in the fact that they are connected to the rib cage via fibrous tissue. Expanding their lungs while being exerted to the pressure of the water above them to breathe in through their snorkel-like trunk requires a lot of force. Being attached to the boney rib cage allows them to achieve this additional force. The fact that no other mammals breathe like this supports the basis that they must’ve evolved specifically for this. Perhaps in millennia gone by it was easier for their predecessors to support their large bodies in the water. One thing for certain, however, is as they started to spend more time out of the water in the harsh heat of Africa the ability to keep themselves cool became paramount.
With such a large body and gut that is continuously processing food, they generate a huge amount of internal heat. Interestingly the internal temperature of their gut stays at a constant 37 degrees Celsius. Comparatively, the external temperature of their skin can reach temperatures of up to 55 degrees Celsius. This is where nature provided an ingenious way for elephants to pump all of their blood through a network of veins in their ears within 20 minutes.
The network of veins lies close to the surface of the skin of their large ears. By flapping their ears and creating a current of cooler air above the ear allows the elephant to radiate heat from these veins into the air before pumping the cooled-down blood back into their bodies. Their large ears certainly are in proportion to their enormous bodies, at least, far more so than their feet.
Although the surface area of their feet is certainly something to marvel at, it is comparatively small considering the immense size and weight they carry. Within the round foot of an elephant are five toes. If you had to look at an x-ray of an elephant’s foot you’d see that they are essentially walking on their tip toes.
Underneath the heel of the foot sits a cartilaginous, cushiony fat pad. As the elephant exerts pressure on the foot this fatty cushion absorbs the weight and expands. The fascinating aspect of this, however, is that as the weight is rolled from the heel to the toe the fatty cushion is primed to recoil like a spring helping the elephant propel itself forward. Certainly a useful attribute for an animal that walks up to 20 kilometres a day!
Are Elephants Still Evolving?
Evolution is constantly happening as more successful genes get passed on from generation to generation. One of the most prevalent signs of this happening right before our eyes casts success in a slightly different light than what we would normally imagine. Probably one of the most noticeable characteristics of an elephant is its tusks. Through decades of both legal and illegal hunting, the average length of tusks seen on elephants currently has certainly decreased. The prize of hunting an elephant with the biggest tusks has, in essence, removed these genes from the gene pool. This is just a reminder that we as humans are equally a part of the world’s ecosystem and can have lasting impacts on the other animals that inhabit it.