Fewer than 40 babies on record have been born with true tails
Humans lost their tails with the other apes, keeping only a small fused tailbone. Yet on fewer than 40 recorded occasions, a baby has arrived with a genuine tail containing vertebrae, an ancestral trait resurfacing. In 2024 researchers reported a mutation that may have helped erase the tail from our lineage in the first place.
Our coccyx usually consists of four fused vertebrae at the base of the spine, the leftover equivalent of a tail, and frogs carry a similar remnant. In a human embryo the tail bud becomes the end of the backbone. Occasionally an infant has a soft tail with blood vessels, muscle and nerves but no bone; doctors class that as an abnormality rather than a true throwback.
Elsewhere in the animal kingdom tails do almost everything. Fish, otters, whales and crocodiles swim with them, cats and kangaroos balance with them, and monkeys and opossums grip branches. Horses swat flies, and foxes curl bushy tails around themselves like blankets. Birds steer with stiff tail feathers, woodpeckers brace against trunks with theirs, and peacocks court with extravagant plumes.
Some tails are weapons or warnings. Scorpions sting, stingrays stab, thresher sharks stun prey, and armoured dinosaurs swung spikes or clubs. Certain snakes wiggle their tail tips as worm-like bait. Deer flash white undersides at danger, beavers slap the water, and rattlesnakes buzz. Geckos go further, snapping off their tails to distract attackers; the regrown tail is usually darker and made of cartilage instead of bone. Some rodents shed only the tail's outer skin to slip free.
Even a mouse's tail relies on dedicated wiring. Researchers traced a pathway from a balance centre in the brainstem down to tail motor neurons in the lower spinal cord. Stimulating it with light produced the strongest tail movements when the mice were balancing on a narrow ridge or being gently knocked off balance, showing the brain recruits the tail specifically to keep the body steady.
Source: Tail
