The similarities between humans and pigs

‘You’re a pig!’ It might be a common insult but, interestingly, there are a number of similarities between humans and pigs. These include various anatomic and physiologic traits, such as organ placement (and often size and function), skin similarities and some disease progression.

A pig weighing around 60 kilograms will, for example, resemble a human body in many ways, including fat distribution, cover of hair and ability to attract insects. For this reason, pigs have been used in medical research for over 30 years, and are what’s known as a translational research model. This means that if something works in a pig, it has a higher possibility of working in a human.

So do these similarities mean that humans are closely related to pigs? Not necessarily. Many of these shared physical traits are not the result of a close ancestry, but rather of convergent evolution—that is, selection of the same characteristics by a common environment. Phew, you  might say—your bedroom might resemble a pigsty but at least you’re not related.

But what about on the genetic level? Well, that might be a different story. Comparison of the full DNA sequences of different mammals shows that we are more closely related to mice than we are to pigs. We last shared a common ancestor with pigs about 80 million years ago, compared to about 70 million years ago when we diverged from rodents.

A new study has revealed a potential hidden evolutionary link between pigs and primates. Genetic elements called SINES (short interspersed elements) are usually considered to be ‘junk DNA’, left behind by marauding viruses. However, these elements may hold additional clues about our mammalian evolutionary history.

In humans, the most common SINE is the Alu transposable element, which is derived from the small cytoplasmic 7SL RNA. The latest research has revealed that 7SL RNA is also the original source for a common swine SINE. Just a fluke? Unlikely, according to researchers, who think that this SINE must have had a common origin. This suggests that there are close parallels between the evolution of this element in pig and primate lines, whereas it died out in the rodents.

Some scientists believe that the results are ‘convincing enough to classify the suidae (swine) into a family mainly inhabited by primates’, though the evidence from the entire genome disputes this. The genome is a complex puzzle. Bits of it came from different sources and evolved at different rates. While some pieces may match, you need to look at the entire genome to really understand the full picture. Geneticists are busy analysing all aspects of the human genome, including its previously overlooked SINES.

So, if you snort when you laugh or pig out at dinner, don’t fret—you’re still human.