An Anatomical Feature In Our Arms Is Proving Humans Are Still Evolving

The emergence of a third artery in the forearm could benefit us by increasing blood flow. Tanawat Palee/Shutterstock

A new study published in the Journal of Anatomy has proven that Homo sapiens (that’s us) aren’t done with evolution yet. An investigation by researchers at the University of Adelaide has discovered that our forearms contain compelling evidence that we are still evolving, albeit on a small scale, as the prevalence of a blood vessel called the median artery has increased significantly since the late 19th century.

During the embryonic stage of our development, the median artery is the main vessel that transports blood to the forearm and hand. In the past, the median artery has disappeared as the radial and ulnar arteries replace it while a baby is still developing in the womb, being an uncommon feature in the adult forearm, but the researchers’ findings reveal that not only is the median artery not disappearing in some individuals but that these people represent an ever-increasing group.

The study estimates that around one in three of us retain this median artery, a statistic that will continue for the next 80 years, but the trend is expected to continue as the median artery becomes more and more common as a permanent feature of the human forearm. When more than 50 percent of people are found to have the “abnormality” it will cease to be abnormal and become the new norm for human anatomy.

Diagram shows the position of the median artery in those who retain theirs after birth. IFLScience

The researchers have termed this change “microevolution”, as while, to their estimations, modern humans are evolving at a faster rate than at any stage in the past 250 years, the change is a small one. If we’d sprouted a layer of skin between our arms and body that enabled us to soar, flying-squirrel-style (chance’d be a fine thing) this would of course be a more significant example of evolution, but we’ll take what we can get.

“Since the 18th century, anatomists have been studying the prevalence of this artery in adults and our study shows it’s clearly increasing,” said study author Dr Teghan Lucas in a statement. “The prevalence was around 10% in people born in the mid-1880s compared to 30% in those born in the late 20th century, so that’s a significant increase in a fairly short period of time, when it comes to evolution.

“This increase could have resulted from mutations of genes involved in median artery development or health problems in mothers during pregnancy, or both actually. If this trend continues, a majority of people will have median artery of the forearm by 2100.”

Exactly what benefits led to the retention of this artery in keeping with Darwin’s “survival of the fittest'' theory of adaptation isn’t clear, but the researchers believe it’s a beneficial anatomical feature as it increases overall blood supply to the forearm and hand. It’s hoped it could even be utilized during surgeries as a replacement for damaged vessels in other parts of the body.

According to the researchers, this arterial microevolution joins a handful of examples that demonstrate how human anatomy is changing over time, including the abnormal connections of the foot, an increasing absence of wisdom teeth, and an increasing presence of a small bone in the back of the knee joint called a fabella.

Senior author Professor Maciej Henneberg said: “This is microevolution in modern humans and the median artery is a perfect example of how we’re still evolving because people born more recently have a higher prevalence of this artery when compared to humans from previous generations.”

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