Yawns, hiccups, prune fingers – we wouldn't be here without them
Published 30/01/2013 | 06:00
Scientists have discovered that the traits and features we no longer need once ensured our survival, reports Tom Rowley
Wrinkly fingers have long been an indicator that it's time to get out of the bath. But now scientists have found that our ancestors evolved the prune-like look for a more practical reason.
A Newcastle University study has concluded that prune fingers are better at clasping objects in water, which, they argue, might demonstrate that our primate forebears needed them to get a better grip when clinging to wet branches and swinging through trees hundreds of thousands of years ago.
Puckered toes might also have helped early man to keep his footing in the rain.
The study marks the latest attempt to make sense of so-called vestigial traits – anatomical adaptations that the human body evolved for a specific purpose, but which are now redundant.
Scientists have been fascinated by the anomalies, ranging from the yawn to the continued presence of the appendix, ever since Charles Darwin attempted to use his theory of evolution to explain them in the mid-19th Century. If these adaptations have no use, why do we not lose them over time?
"You only lose a trait if there is actually a problem with it," explains Dr Tom Smulders, who led the Newcastle study. "As long as it has not been a problem to your survival or reproduction, then it won't disappear."
Darwin was keen on studying the quirks because they helped explain the efficiency of natural selection: how the genes that gave an organism an advantage over its rivals endured.
Prune fingers may once have been vital, according to Dr Smulders's research.
He asked 20 volunteers to move marbles from one hand to another and into an underwater box. Those with wrinkly fingers were 12pc faster than those without.
His research is supported by pictures that show Japanese macaques develop wrinkly fingers when they sit in hot springs, suggesting fellow mammals may have acquired the feature for the same purpose.
So what other traits persist? Goosebumps have no purpose in the modern world, but serve as a reminder of a more brutal era when, under threat, we would make our hair stand on end to appear larger.
Scientists are also examining whether goosebumps are an indicator of dishonesty, appearing when we tell lies.
Yawning also appears pointless today, but it could have been developed to enable primates to monitor air quality in enclosed spaces or, because the act is so contagious, to encourage humans to empathise with and learn from one another, according to Dr Matthew Mason, a physiologist at Cambridge University.
Some traits, such as hiccuping, have been retained as side-effects of more beneficial processes.
As Dr Mason explains: "It can be an inevitable, if unwanted, consequence of something else, which is advantageous and selected for, and you can't lose one without the other."
In the case of hiccups, a reflex to keep the digestive tract working functions too well, causing a "fit" even when there is no problem. "It may not achieve anything very useful, but it is a consequence of having some useful reflexes that help dislodge food and sometimes go wrong," says Dr Mason.
Some of our most common evolutionary "relics" can cause pain.
Not only can appendicitis lead to life-threatening infections, but the appendix has been "useless for a good 100,000 years", according to Dr Robin Allaby of Warwick University.
So why have we not lost the small, worm-like appendage attached to the colon?
"It is generally not a problem," says Dr Allaby, "so there is no selection pressure."
Other scientists have suggested it might act as a reservoir of good bacteria, helping to repopulate the gut.
Its original purpose is better understood.
"It is a throwback to our time of chewing hard plant matter," says Dr Allaby.
"You will see rabbits have a well-developed appendix where you will have a colony of bacteria that will be good at breaking down things such as cellulose."
Similarly, the coccyx – or human tail bone – can be very painful if broken. "It will hurt like hell," Dr Allaby says.
Despite this, it is predominantly harmless and was very helpful when our ancestors used their tails for balance.
There is, though, good news for those who suffer from one painful throwback: wisdom teeth.
They were useful hundreds of thousands of years ago for chewing tough plant matter, but today only lead to visits to the dentist.
"The third molars are in a state of flux," says Dr Allaby. "They will be selected against. They could be gone very, very rapidly. Well, within tens of thousands of years."