While the traditional tale of the horse is told as a linear progression towards horsedom, the truth is that for much of their evolution, multiple branches of horse relatives – of different sizes and toe counts – coexisted across the varied habitats of our planet. By elongating their limbs and reducing their toe-number, some of these horses became swift grassland runners that could cover greater distances. At the same time, their teeth changed shape to shear tough grass instead of chewing soft leaves, and grew longer to counteract a lifetime of abrasion. By around eight million years ago in one lineage of horses – the equine equids – the single middle toe had become a sole weight-bearing hoof. They were the ancestors of today’s horses.

    Recent research, however, suggests the picture is not so simple. Evidence of the second and fourth digits of the horse’s foot are still visible, greatly reduced and incorporated into the dominant digit as though giving us the permanent middle-finger. But a team of researchers in America have been taking a closer look at horse limbs. They believe they can still find the remnants of the inner and outermost digits incorporated into the scant second and fourth digits. This gives palaeontologists and evolutionary biologists a new perspective on the mechanisms that allow animals to reduce their digits and limbs. It also reminds us that even when we think we understand something completely, it pays to look twice.

    The horse is worth ongoing research not just because it is an evolutionary and biological marvel, but also because it’s an anthropological one. “Domestication of horses revolutionised human history,” says Professor Ludovic Orlando from the Natural History Museum of Denmark. “With horses, we travelled way faster, and could transport goods, people, germs and culture at unprecedented speed.

    “In short, horse domestication is a turning point in history.”

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