Curved Spine Deals With Tension

Biological Strategy

Three-toed sloths

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Image: Bill Green / Flickr / CC BY - Creative Commons Attribution alone

Manage Tension

When a living system is under tension, it means there is a force pulling on it, like a person pulling on a rope tied to a horse. When applied to a living system, unless the system is completely rigid, the result is that it gets stretched. If stretching exceeds the strength of the living system’s material, it can damage it. Living systems manage tension using materials that are flexible and stretchable enough to survive most tension that occurs in their environment. The ocean’s intertidal zone offers a good example. The waves and incoming and outgoing tides put tension on soft-bodied organisms. Mussels resist tension with flexible threads that hold them onto rocks; in contrast, large algae have stretchy fronds.

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Mammals

Class Mammalia (“breast”): Bats, cats, whales, horses, humans

Mammals make up less than 1% of all animals on earth, but they include some of the most well-known species. We know first-hand some of the characteristics that make mammals unique, like having hair, being able to sweat, and producing milk through mammary glands. Another critical shared feature is a set of highly-specialized teeth. Unlike sharks or alligators, for example, whose teeth are generally all the same size and shape, mammals have differently shaped teeth in different areas of the jaws to target specific foods or foraging strategies.

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The spine of a sloth supports its body weight under tension via curved shape.

“The sloth spends most of its life hanging upside-down from branches. Its skeleton therefore has to cope with tension rather than compression. When it leaves its tree, its belly drags on the ground, because its curved spine is designed to support its body weight from below, not from above, and its legs are too weak to support it.” (Foy and Oxford Scientific Films 1982:37)

Foy S, Oxford Scientific Films. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J. M. Dent & Sons Ltd, London; 1982. 238 p.

Last Updated August 28, 2020

References

Book

The grand design: Form and colour in animals

01/01/1970 | Sally Foy

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