Wings on a flightless bird, eyes on a blind fish, and sexual organs on a flower that reproduces asexually—what’s the point? These vestigial organs and structures, once useful in an ancestor and now reduced in size, complexity, and/or utility, transport important information and give us indications into our evolutionary past.
Interestingly, vestigial doesn’t necessarily mean useless. Since the above structures can be traced back through the ancestors, they basically serve as a marker of evolution; no living being can have a vestigial organ that hasn’t been found in its ancestors.
Similar in concept are atavisms. These are the recurrence of a structure or trait that isn’t present in the immediate ancestors. For example, whales and dolphins have been found in nature with hind limbs – the re-emergence of a trait inherited from their terrestrial ancestors.
Humans also contain structures that mark our origin. Let’s have a look at three evolutionary leftovers in the human body.
One remarkable example of an atavism is the human coccyx or tailbone, which is a relic of the mammalian tail. Valued by mammals for balance, species-to-species signalling, and support, the tail is absent in apes and in humans. However, all human embryos initially have a tail. Normally, they revert into four to five fused vertebrae (the coccyx). Regardless, there have been numerous case studies of babies being born with an extended coccyx—a tail—that have then been removed without incident.
Our herbivores ancestors required strong molars for mashing up and chewing plant material. This relic is why many of us will grow wisdom teeth. Supposedly, they could still be used for chewing, but in one-third of people, they can come in sideways or impacted, which can then lead to pain and infection. This is why they are almost always extracted when they start to develop.
Another leftover from our herbivore ancestors is the vermiform appendix, which is an organ attached to the large intestine. A similar, much larger sac is seen in other animals and is used to help in processing high cellulose diets. While appendicitis can be a potentially serious condition and removing the appendix has no adverse effects, some researchers think that the appendix might display an auxiliary function, such as aiding the immune system.
Besides the previous examples, there are other vestigial and atavistic structures in humans. And if they don’t need too much energy or resources to produce, odds are, they’ll stick with us for the long haul!