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Dominance and Hierarchy

I have argued that a herd of horses is much like a school of fish or flock of birds, leaderless and choosing a course of action via collective decision making. I have argued that “respect” as is normally meant by humans, does not exist in the horse, and that humans often use it as a euphemism for “fear”. I do not dispute the existence of “dominance” in a herd of horses, but I have questions about what it is and whether the concept is useful. Thirty years ago, researchers were far from a consensus on how to define and measure dominance, and little has changed since then. Anything gets harder to talk about when we can’t agree on what it is.

Eating and Digestion

Grass Loves Horses

Horses are grazers. “Graze” comes from Middle English grasen, from Old English grasian, and that from græs, grass, so a grazer is a grass eater. Horses are grazers, as are cows, sheep, bison, buffalo, deer, elk, wildebeest, zebras, and kangaroos.

Special saliva. When a mammal or a plant-eating insect eats dinner, it creates saliva, some of which it leaves on the grazed grass. For over 40 years, scientists have known that grasshopper grazing increased the growth of the grass they ate. In 1980, Dyer applied a component of mouse saliva — epidermal growth factor (EGF) — to sorghum seedlings, and found this significantly increased the speed at which shoots and roots grew, and found that such growth was dose-dependent: more saliva meant more growth. EGF is not only found in grasshopper saliva. It is also found in mammalian saliva (including yours) and in spitballs.

The Mind of Your Horse

The brains of mammals are very similar, and differ in degree rather than kind.

The human desire to believe that we are the most intelligent species has led to a number of comparisons of brains. Brain size must matter, but our brains are smaller than those of the elephant or whale. Some researchers find pleasure in noting that some parts of our brain are much bigger than the same parts in other animals. For instance, our friend Cowboy Bob reports that “the brain cavity of a horse is filled with a lot more than what we usually think of as the “brain.” Although the space would, in fact, hold a small grapefruit, the cerebral hemisphere — or “thinking” portion of the brain cavity is a lot smaller.”

If horses could talk, though, they might point out that the brain cavity of their skulls is about the size of ours, and that lots of preprocessing happens between the nostrils and the brain, and between the eyes and the brain. If we compare head size of Mr. Horse and Mr. Man, Mr. Horse does just fine.

Smell

Even if words fail us in talking about chemicals, olfactory receptors don’t let us down. In a mammal’s nose, each olfactory neuron possesses a single type of receptor; each receptor responds to several molecules, and each molecule is recognized by several receptors. Scents are discriminated by various combinations of 10 or more receptors. With 350 types of receptors, the number of ways you can produce combinations of 10 is ridiculous. As I’ll show you later in this chapter, a horse can detect about 1,816,285,375,084,304,096,155,409,990,400 different scents. That is about 1,699,868,436,439,970,000,000,000,000,000 more scents than your dog. And it is more than the number of chemical compounds possible. The perfect nose could detect stuff that doesn’t even exist! My old nose doesn’t do so well, but the nasal cavities of Mr. Horse are filled with possibilities.

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