‘Why I believe the sloth is a hero of evolution’

The slow shall inherit the earth? Lucy certainly hopes so.
by Lucy Cooke

Zoologist and award-winning producer of wildlife documentaries, Lucy is a master of sloth propaganda. She wrote A Little Book of Sloth and founded the Sloth Appreciation Society.

Why do fast-moving and glamorous animals get all the attention? The sloth has been much maligned, but in fact this tree-hugger is one of the success stories of adaptation.

People say, what’s in a name? Well, quite a lot when it is a synonym for a deadly sin.

Yes, the sloth was damned from the moment it was named after one of the world’s most wicked transgressions – a pretty damaging public relations blow by anyone’s standard, and one that has led to the sloth becoming one of the most maligned and misunderstood animals on the planet.

I think it is time the sloth reclaimed its name from sin and received the respect it deserves as one of planet Earth’s supreme survivors: a miracle of evolution, perfectly adapted to its slow arboreal lifestyle.

Anti-sloth propaganda began the moment the early Catholic explorers first set foot on South American soil. The first to describe a sloth, Georges Buffon, had this to say in 1749:

‘Slowness, habitual pain, and stupidity are the results of this strange and bungled conformation. These sloths are the lowest form of existence. One more defect would have made their lives impossible’

Buffon, or buffoon as I like to think of him, had clearly missed the point. Thanks to Charles Darwin we now understand that natural selection weeds out the weak. So there is nothing defective about the sloth – it is, in fact, a very successful animal.

In tropical jungles sloths make up as much as two thirds of the mammalian biomass, which is biology speak for ‘I’m doing rather well thank you very much.’

It may not be as glamorous, but as a survival strategy sloth-like slowness is arguably better than speed. Just ask the cheetah. Unlike the sloth, the Ferrari of the animal world is highly endangered and suffers humiliation and hard work to survive.

The cheetah must outrun the antelope or it won’t eat. So it has evolved for short bursts of speed but not strength. It is a little known fact that cheetahs lose up to half their kills to hyenas because they cannot risk getting damaged in a fight. They are in fact a bunch of wimps – something hyenas find highly amusing.

The sloth has taken a much more stealthy approach to getting its dinner. It survives by capturing and consuming very slow moving leaves. But leaves don’t want to be eaten anymore than antelopes do: they are extremely hard to digest, full of tough fibre and toxins.

So the sloth has also evolved into an athlete. A digesting athlete. It takes a sloth one whole month to break down a single leaf. If it did it any quicker, it would literally poison itself.

To cope with this digesting marathon it has a four-chambered stomach and a body that is designed to use up as little energy as possible. It hooks on and hangs from the trees like a big digesting bag, sleeping off the effects of its favourite Cecropia leaves, which contain alkaloids with a similar property to Valium.

And since running from danger is not an option, nature’s couch potato’s final stroke of genius is to become a master of disguise to avoid being eaten. Its fur contains algae and bugs and it has no natural body odour. It looks and smells just like a tree.

So forget being fast, it’s overrated. The slow shall inherit the earth.

Lucy’s latest series Meet the Sloths starts on Animal Planet on November 14 at 8pm.

You Decide

  1. Are we too impressed by beautiful, glamorous animals like the cheetah, at the expense of ugly and overlooked species?


  1. Pick your own animal to celebrate, and write an article like this one to defend its virtues.

Word Watch

Sloth, meaning laziness or idleness and the avoidance of physical or spiritual work, is one of the seven deadly sins in traditional Christian morality. The others are pride, envy, gluttony, lust, anger and greed.
South American
Lucy has filmed the sloths in Costa Rica, but they are found in rainforests all over Central and South America.
Charles Darwin
Darwin (1809-1882) devised the theory of natural selection, which proposes that a species gradually becomes adapted to its environment as organisms with useful traits survive to pass them on to their offspring. This explains how life evolves and why some plants and animals flourish while others fail.
A tranquilising medical drug.

PDF Download

Please click on "Print view" at the top of the page to see a print friendly version of the article.