Why do Three-Toed Sloths Come Down From Their Trees to Defecate?

Our bodies are most robust and most fragile at the same time. Recently completed the excellent book Evolution gone wrong the curious case why our body fails us? by Alex Bezzerides

Well written and extremely fun to read. Filled with many funny but insightful why questions. Here’s a small sample from the book on pooing sloths?

Why do three-toed sloths come down from their trees to defecate?

On the surface, this behavior is baffling. Why risk the chance of encountering a predator? Why not just let it fly from the branches? In class, my students work together to develop hypotheses and design hypothetical experiments to test their hypotheses. Are sloths fertilizing their trees in a targeted manner? Is it some way of marking their territory? Is it an atypical type of mate attraction?

Acutely observant scientists solved the mystery only recently with a great deal of patience.

They first observed that sloths have algae growing in their fur, which gives the sloths a green tint. The algae help the sloths blend in with the forest canopy, but the story goes beyond organic camouflage.

The sloth scientists noted sloths feeding on their homegrown algae and in doing so, supplementing their otherwise nutrient-poor diet. Eating their own fur algae is admittedly weird, but it gets even stranger than that.

A population of moths lives in the fur of each three-toed sloth. The moth population increases the nitrogen content of the fur and thus promotes the growth of the algae the sloths snack on.

When the sloths make their weekly treks to the bottoms of trees, the female moths lay their eggs in the fresh sloth dung. The tidy sloths cover up their mess with some leaf litter, and after the eggs hatch, the moth caterpillars dine on the sloth poop, grow up, become adults, and fly to the canopy layer to colonize sloths just as their parents did.

Sloths risk their lives to make a dung nursery for the moths on whom they depend for fertilizer to grow the algae they not only use as camo but also eat from their own fur for an extra shot of nutrition. Bam! Mystery solved. We can finally let the sloths poop in peace. Next question.

I hope this sloth-and-moth story has made the point that ultimate questions are fascinating to consider. They push researchers in completely different directions compared with proximate questions. The answers to ultimate questions are also often wildly unexpected.

This is what the book delivers answers to the ultimate questions on human anatomy? Do give it a read if you get a chance?

Do you have other interesting books to recommend, please let me know in the comments below?

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