Horses and their human riders can develop such a close connection that the two go into a state of co-being, according to a paper published in the latest issue of the journal Social Anthropology.

The phenomenon may be unique between horses and riders, since both move as one and often physically change over the course of the relationship to conform to the other. Intense cooperation is also key.

"Cooperation means attuning to each other," lead author Anita Maurstad of the University of Tromso's Department of Cultural Sciences told Discovery News. "The rider is often in charge, expressing, through body kinetics, what he or she wants the horse to do, but unless the rider attunes to the horse's body and mind, the horse will not understand, and unless the horse attunes to the rider, the horse will not manage to perform the requirements of the rider."

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"So co-being is, on the one hand, about moving together, but also about being together on the ground, communicating as individuals, and in order to communicate, a shared sense of the other must be in place," Maurstad added.

For the study, Maurstad and her team gathered data on horses as well as prior papers concerning the horse-human relationship. They also interviewed 60 riders from both Norway and the Midwestern United States. The riders participate in different equestrian sports and ride within a variety of local settings.

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Nearly all of the riders mentioned feeling the "shared sense of co-being" with their horse. Bella, an experienced dressage rider, for example, described it as follows: "I actually feel part of the animal, reacting to his body and my body."

This feeling is not just mental, as skilled riders grow new muscles in their legs, butts and other parts of their body to match the body of their particular horse. The horse, in turn, will exhibit physical changes in response to the shape, load and repeated motions of the rider.

Horses are very sensitive to touch, so when a horse and rider are familiar with each other, an experienced rider need only to twitch a muscle to communicate desired direction on a trail.

Keri Brandt, a sociology professor at Fort Lewis College, proposes that "humans and horses co-create a language system by way of the body to facilitate the creation of shared meaning."

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Humans additionally change the way they talk in order to better communicate with their horses.

"The term "motherese" is used to refer to the way many humans talk to their horses," co-author Dona Davis of the University of South Dakota’s Department of Anthropology and Sociology told Discovery News. "It is not 'baby talk,' but a controlled and calming tone of voice. People use this language tone so as not to excite the horse. I see it as a kind of verbal stroking."

Co-author Sarah Cowles, also from the University of South Dakota, added that a horse and its rider also become accustomed to each other's smells. Horses have adapted their ways of relating to other horses to the manner in which they respond to humans.

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Leanne Proops, a researcher at the University of Sussex who has also studied the horse-human relationship, told Discovery News, "Horses are highly social animals that use very fine body and facial movements to communicate with each other ... Wild equids are sensitive to changes in body posture of conspecifics (other horses) and also are sensitive to the behavior of other species that form mixed herds."

Proops added that the process of domestication might have enhanced the ability horses possess to understand humans.

Could horses then be man's true best friend in the animal kingdom, perhaps surpassing even dogs and cats in terms of loyalty and level of connection? Prior studies do show that horses possess incredible memories, never seeming to forget favorite familiar humans, even after years of separation.

Many of the riders in the study reported having other pets at home, and indicated that they valued them all for different reasons, but the exhilaration of feeling completely in sync with a horse appears hard to match.

As rider Bella shared, "It's that connection that you start craving. Once you have it, you need more."