A Wilder View: Why humans don’t have tails

Posted at 1:01 PM, Mar 30, 2022

MISSOULA - This edition of A Wilder View dives into why we don’t have tails.

Around 500 million years ago our ancestors developed tails. It first started with fish using their tails to swim in the oceans. And since then, they have taken on tons of different roles. From birds using them to move swiftly through the air to using tails as energy storage like beavers. But, more than anything, tails are used for balance.

Today primates such as monkeys still have their tails. But 20 million years ago, when apes first appeared no tail was to be found. As people have evolved from apes, we of course do not have tails.

Charles Darwin first recognized this change in our ancestral lineage. Explaining that although we lack a visible tail a remaining set of vertebrates extending past the pelvis known as the coccyx is what remains of our ancient tails.

To learn why we don’t have tails, take a look at how we walk. People walk completely upright on two legs. This gives us a large advantage in energy expenditure. Four-legged animals use more energy moving all their legs.

While people take advantage of two legs and the help of gravity allowing us to use 25% less energy than walking on four legs. And saving energy in the wild can be the difference between life and death.

Having our heads at the top of our bodies and not in front also eliminated the need for a tail to counterbalance this weight shift.

Now research points to a genetic mutation that may have omitted our tails. To see if the mutation is the cause for the loss of our tails, scientists genetically altered mice DNA to have the same mutation. When the genes were changed, tails on the mice disappeared.

This does not definitively prove that this mutation is the cause of our lack of tails but is the closest conclusive evidence that researchers have found. This finding suggests our ancestors lost their tails abruptly, instead of over a long period of time. Which actually aligns with the fossil record.

For something to be lost so quickly is quite significant as usually millions of years of tiny changes gradually lead to this modification.