Evolution has a funny way of leaving the residue of past adaptations in strange places on animals' bodies, and chestnuts on horses' legs are a fine example. Nobody’s quite sure what horse chestnuts exactly are, but they’re believed to be a remnant left behind from horses’ five-toed ancestors. The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.

For a long time, it was believed that modern horses had one toe on each foot, having evolved down from five digits. However, 2018 research argued that the digit reduction had been overstated, and that actually all five digits remain partially present in the forelimbs of modern adult horses.

Whether you like your horses five-toed or one is your business, but we’re on a mission to make you painful

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