Size matters in the animal world. In colder climates, being large helps minimise the loss of body heat. For a large predator, body size may be the key to overpowering its prey. Whereas, for a large herbivore, like a bison, body size may be its greatest defence. And, even within a species, the size of an individual will often determine its success in finding a mate and reproducing. A big body brings a host of evolutionary advantages, so why is it that some species have downsized? Welcome to the miniature world of pygmy animals!
Body size and survival
To begin with, we need to remember that the natural world isn’t an assortment of individual species, but an interconnected web of life. Across different habitats, species are tied into intricate ecosystems. The evolution of a species, therefore, is shaped by a vast range of factors. Everything from climatic conditions, amount of resources, abundance of rival species, predators and prey. Plants and wildlife must find their niche if they are to survive.
A clear example of this is described by Bergmann’s rule, which is based on the simple observation that larger species are found in colder regions, and smaller species are found in warmer ones. The reason for this is that larger animals have a lower surface/volume ratio than smaller animals, so they lose less body heat. For endothermic animals like the walrus, which live in the arctic, this energy efficiency is an essential advantage. For some reptiles and insects, which rely on external heat for energy and growth, the opposite rule applies.
Interestingly, these patterns can be observed over time as well as space. During the Paleogene era (66-23 million years ago) there was a series of extreme global warming events, causing widespread mammalian dwarfism. Some species shrank by as much as 20%.
In humans, dwarfism is often categorised as either proportionate or disproportionate. In the former, the individual’s limbs and torso are unusually small, whereas the latter only affects the size of an individual’s limbs.
Dwarfism can occur because of a number of hormonal or genetic conditions. One of the most common causes of disproportionate dwarfism is achondroplasia. This is an autosomal dominant genetic disorder, which means that it can be passed on by either gender snd only one parent need carry the gene for an offspring to be affected
Another form of dwarfism, which explains the evolution of pygmies (human and animal) is the process of insular dwarfism. This evolutionary phenomenon, connects the size of an animal to the relative abundance (or scarcity) of resources.
In isolated habitats, such as islands, caves and desert oases, where resources and territory are limited, there is a selective advantage to being small. For herbivores, fewer competitors and predators facilitate further dwarfing. Similarly, as prey is smaller, the selective advantage of size in large predators also decreases.
We’re obsessed by extremes in size. Children’s books and toys are dominated by Africa’s big mammals and there’s no shortage of nature documentaries about ‘the world’s biggest predators’. But, when it comes to pets, the opposite seems to be true. There’s a growing trend in breeding miniature versions of every conceivable domestic animal.
When you look at pugs, corgis and dachshunds, it’s hard to believe that these dogs evolved from wolves! The dwarfing in these species, characterised by shortened limbs due to improper bone growth, is the result of achondroplasia.
While in the wild this kind of mutation would likely pose a disadvantage, in captivity it’s proven to be desirable. Over centuries, breeders have selectively bred for these mutations, developing dogs to meet mankind’s hunting, herding and companionship needs.
If you type ‘pygmy’ in Google search, pygmy goat is the first thing you’ll find. On Youtube there are no less than 84,900 pygmy goat videos!
Pygmy goats, just 40-60cm tall, originate from West African dwarf goat. They were brought to Europe by the British during colonial times and later exported to the US. Now they are hugely popular on account of their small size, good nature and hardiness.
Another viral pet obsession of the last decade is that of pygmy pigs. You’ve probably also seen them referred to as teacup pigs, however this is not a recognised breed. Most of pigs that are bred as pets are, in fact, Vietnamese pot-bellied pigs. Although they are naturally smaller than other breeds, ‘teacup pig’ or ‘micro pig’ are deceptive labels.
Don’t be misled, the photos you’ve seen of teacup pigs online are invariably of piglets, not adults. What’s more concerning is that their unnaturally miniature size is often a result of deliberate malnourishment or the breeding of unhealthy, under-sized runts, a practice which perpetuates health problems.
Due to the selective pressures of the natural world, pygmy species will only proliferate in the wild if being small is advantageous. Nature cares little about how adorable you are!
As I mentioned before, this is most likely to take place in isolated areas, through the process of insular dwarfism. Here are some of our favourite wild pygmies from the animal kingdom.
Borneo pygmy elephant
The pygmy elephants of Borneo are the smallest elephants in Asia, but a fully-grown adult can still weigh up to 5,000kg. They are significantly larger that their natural predator, the sumatran tiger, which tends to only hunt elephant calves. Human activity poses a far greater threat, directly through poaching for ivory, as well as indirectly through deforestation and farming, leading to habitat loss.
Weighing just over 100 grams, the pygmy marmoset (Cebuella pygmaea) is the smallest monkey on Earth. They inhabit the rainforests of the western Amazon Basin and display a remarkable feeding habit. They live almost exclusively on the sap of gum trees. This marmosets make hundreds of holes in the bark of different trees with their sharp teeth and feed on the sap for hours a day. Another interesting fact is that they are one of the only primates that can give birth to non-identical twins.
Brookesia micra (main picture) is the latin name of the smallest chameleon on Earth. It was discovered around 10 years ago on Nosy Hara, an islet off the coast of Madagascar and is another example of the process of insular dwarfism. They live in leaf litter on the forest floor during the day, and climb up into tree branches at night to sleep. With a maximum length from snout to tail of just 29mm, it’s a wonder that scientists managed to find it at all!