A gene that we share with some small marine animals caused, millions of years ago, the emergence of brains in vertebrates, the origin of cognition and consciousness in complex life.
Cognition is the faculty that allows us to process information that comes from the senses and, although we have a clear idea of how living beings have been formed and evolved, it remains a mystery How did this cognitive ability develop? from the point of view of biology.
A new investigation, led by the University of Oxford, has come to shed some light on the biological process that allowed living beings, at some point in evolution, not only to become aware of the conditions of their environment, but also to that they exist and are part of a complex world that they must learn to manage in order to survive and hone their skills.
We know that, at the beginning of complex life, the first organisms did not have a brain, but a network of neurons distributed throughout his body that finally ended up concentrating in a specific organ, responsible for processing sensory information and lighting cognition.
We do not know how this evolutionary feat was produced, but the new research, in which Ute Rothbächerfrom the Department of Zoology at the University of Innsbruck in Austria, provides an explanation of the biological mystery that led organisms to equip themselves with a regulatory organ of what we call cognition, housed in a new biological structure called the head.
This improved head allowed for a wide spatial distribution and multiplication of sensory cells and therefore a much better perception of the environment, the researchers explain in a statement.
To reach this conclusion, the authors of this research studied a simple marine invertebrate, the sea squirt. Ciona intestinalisbelonging to the sister group of vertebrates, the tunicates.
These animals are like living fossilssince they can tell us how the evolutionary precursors of our organisms were: like the current tunicates, they were full of scattered neurons before they evolved and formed a head to house a brain.
In the same way as our evolutionary precursors, current tunicates do not have a well-developed head, but they do have groups of neurons distributed throughout their bodies that are articulated around a kind of dorsal thread.
These groups of neurons form a series of nerve nodes that absorb a wide range of information from the sensory organs through a few cranial ganglia that can merge and form a cerebroid gangliongerm of a potential future brain.
From this cerebroid ganglion, located above the pharynx, derive some nerves that go to the muscles of the rest of the body and coordinate reactions to environmental stimuli.
The novelty provided by this research is that these tunicates contain a shared gene with modern vertebrates, that would be the earliest origin of what a brain could be in the evolutionary history of complex life.
The authors of this research consider that, when the development of living beings was still limited to the seas, the transition from purely invertebrate living beings, with structures similar to heads, to animals that developed new types of heads, capable of to house numerous networks of neurons.
They add that, if the head had not appeared in evolutionary development, the development of sensory cells and nerve nodes that interpret signals from the environment probably would not have occurred. We would be unable to write or read this article.
The new research shows that vertebrate cranial ganglia are based on genetic codes and processes found in tunicates: it found that a gene called “Hmx” was instrumental in the formation of their cranial ganglia.
He found that the cranial ganglia building instructions contain the “Hmx” gene, which has maintained its original function and structure over time: it would have played a role in the centralization of the nervous system.
Probably, the researchers conclude, this gene was already found in the common ancestor of tunicates and later vertebrates.
What this research suggests is that, if higher vertebrates, like us, have a shared gene with current tunicates and their ancestors, this means that we share a common past, the origin of the brain and all its cognitive derivatives in more complex organisms.
Put another way, this discovery suggests that vertebrate brains are recycled products of the primitive cognitive apparatus of irrelevant marine ancestors similar to tunicates, which populated the Earth millions of years ago.
Hmx gene conservation identifies the origin of vertebrate cranial ganglia. Vasileios Papadogiannis et al. Nature (2022). DOI:https://doi.org/10.1038/s41586-022-04742-w