One of the coolest aspects about the human body is that it is completely symmetrical; we have two ears, two eyes, two arms and two legs, making us virtually the same on either side. Scientists have long studied why humans possess this form of bilateral symmetry, what evolutionary advantage this allows us, and where we inherited it from, but research has always proved inconclusive. In her recent study, Professor Elena Temereva of the Department of Zoology at the Faculty of Biology at Lomonsov Moscow State University poses a new theory about where humans received bilateral symmetry from, and it may link us to creatures with tentacles.

Most scientists agree that the ancestor of Bilateria came into being at the end of the Vendian period, or the last geological period of the Neoprotezoic Era, lasting from about 635 to 541 million years ago. The Vendian seas were filled with all types of complex and simple organisms, most displaying the radial symmetry still found in sea creatures today.

An older theory of where we inherited our bilateral symmetry believes we received this evolutionary distinction thanks to one of the simpler organisms of the Vendian sea. According to this theory, a worm without appendages or a coelom, the main body cavity within organisms that protects internal organs, was the last common bilaterian ancestor. This worm was also believed to have a simpler nervous system. The theory, which exists outside of Russian scientists’ line of thought, believed that the coelom appeared later on, independent of this worm ancestor.

The second theory, originally proposed by British Zoologist Adam Sedgwick and accepted by Russian zoologists, suggests that our common bilaterian ancestor did come from a complex coelomic organism. It is also believed this organism possessed appendages for mobility, and food collection, along with a complex nervous system. This view suggests that the coelom of this organism underwent many changes due to a variety of evolutionary factors. In addition, this common bilaterian ancestor descended from a coelenterates ancestor that had radial symmetry and many chambers in the gastric cavity that are essential for coelom development.

Temereva decided to study this theory further, finding new evidence to support this second view, which she published in the journal PLOS ONE. She conducted her research while studying Lingula anatine, one of the oldest brachiopods still present on earth today, dating back 500 million years ago. The fossils of Lingula can be found all over the world, in places like Europe, Southeast Asia and North America.

Through this type of brachiopod, Temereva was able to find our connection with creatures possessing tentacles. “Our study shows that there is a group of Lophophore animals among the Bilateria,” Temereva said in a recent press release. “The lophophore is a special organ that carries tentacles. Phoronoids, barchiopods and bryozoans have collectively been called lophophorate, because they have [tentacles].” Temereva also notes, “Multiple molecular phylogenetics data shows that there is no united group of Lophophore animals.”

Her research, however, proves otherwise, suggesting that a group of lophophore animals does exist. Using immunocytochemistry techniques, laser confocal microscopy, 3D reconstruction, and transmission from electron microscopy, Temereva was able to find that the lophophore group descended from a common ancestor which had tentacles.

“By virtue of the fact there are tentacles among the two main taxons of bilaterally symmetrical animals, it is logical to assume that the common ancestor also had them. It means that the common ancestor of chordate animals including people also had tentacles,” Temereva said.

By finding this new link between complex organisms with tentacles to the creation of our bilateral ancestors, we are one step closer to discovering the history of our evolutionary traits, ultimately allowing us to understand origins better than ever before.

Sources: Sedgwick, A. On the Origin of Metameric Segmentation and Other Morphological Questions. Quarterly Journal of Microscopial Science. 1885.

Temereva E, et al. Modern Data on the Innervation of the Lophophore in Lingula antina (Brachiopoda) Support the Monophyly of the Lophophodrates. PLOS ONE. 2015.