Opening Pandora’s genetic box:
Cephalopods’ brains, another way of thinking outside the box
The founding father of modern biology, Charles Darwin, once said that “the difference in mental states between animals, great as it is, certainly is one of degree and not of a kind” (Darwin, 1888). A peculiar group of animals, cephalopods (comprising octopuses, squids, cuttlefishes, and nautiluses) are an ancient clade of invertebrates whose origins date more than 500 million years ago. They are the owners of an unparalleled intelligence and complex behavioral repertoire. The cephalopod brain is the largest and most complex of all invertebrates, allowing them to solve numerous challenging problems, such as how to escape from a glass jar closed with a screw top. Certainly, these animals literally think outside the box. Yet, no known cognition is so unusual and fascinating, and its evolution is still a mystery. So why do animals without a central nervous system have such sophisticated intelligence? Our answer might be closer than you think and lies in the depths of the microcosmos of their genetic constitution.
The distinctive nervous system of coleoid (soft-bodied) cephalopods is only comparable with the vertebrate bauplan in terms of its anatomical specialization and the number of interacting neurons. A multidisciplinary team of scientists, led by Nikolaus Rajewsky from the Max Delbrück Center in Berlin (Germany), published in Science Advances fascinating results about the evolutionary emergence of the unique brain complexity of octopuses.
The genetic behind the scenes of the evolution of complex intelligence
RNA (Ribonucleic acid) is a molecule essential in coding, decoding, regulating, and expressing genes. Among its different types, microRNA (miRNA) are single-stranded, non-coding molecules involved explicitly in RNA silencing and post-transcriptional regulation of gene expression, which controls how genes will be.
Despite being invertebrates, cephalopods possess a unique miRNA regulation mechanism reflected in the impressive expansion of their basal genetic repository. According to the study, this outstanding clade has three main genetic innovations. The first advantage was the expansion of miRNA gene repertoire, which was previously reported to occur only in vertebrates. This evolutionary benefit is manifested as the enlargement of 3’UTRs, the targets of miRNAs. Moreover, novel miRNAs are specifically expressed in the brain during development. In cephalopods, these novel miRNAs are strongly expressed during the growth of neuronal tissues and axonal connections. Furthermore, target sites of novel miRNA are highly conserved in these remarkable species. Interestingly, genetic conservation across large evolutionary distances suggests these sites are functionally crucial during neural tissue development. These genetic novelties have resulted in a significant evolutionary advantage for cephalopods. Once under natural selection, miRNA enhanced the strength of all developmental processes, which increased their heritability, thus allowing for the evolution of new cell types and, eventually, the emergence of anatomical and behavioral complexity.
The evolution of intelligence and our place on the planet
The analyses demonstrated that the evolution of cognition in cephalopods is associated with post-transcriptional regulation of RNA, only a feature discovered in vertebrates until now. This research is highly significant since it finds comprehensive molecular design principles under selection behind the morphological and behavioral complexity in animals.
Cephalopods are an island of mental complexity in the sea of invertebrates. Because the most recent common ancestor of humans and cephalopods was so simple and laid so far back in the evolutionary past, the latter conforms to an independent experiment in the evolution of complex behavior. Peter Godfrey-Smith stated, “if we can make contact with cephalopods as sentient beings, it is not because of a shared history, not because of kinship, but because evolution built minds twice over. This is probably the closest we will come to meeting an intelligent alien” (Godfrey-Smith, 2016: 9).
That cognition is so alien to us because there are 518 million years that separate our common ancestors. All that evolutionary diversity should not be taken lightly. On the contrary, measuring how the genotypic and phenotypic components that mediate intelligent behavior change over time is the state-of-the-art method to study the evolution of what makes us unique, our brains. As Homo sapiens (literally, wise man), we now understand that our cognition is just one peculiar type among the constellation of solutions evolution has tested over and over. Studying the full array of diversity nature offers to enhance adaptation will contribute to our understanding of the evolution of intelligence and, ultimately, our role on this planet as sentient beings.
References
Darwin, C. (1888). The descent of man and selection in relation to sex. Murray.
Godfrey-Smith, P. (2016). Other minds: The octopus, the sea, and the deep origins of consciousness. Farrar, Straus, and Giroux.
About the author:
I am a Ph.D. candidate in Anthropological Sciences at Stony Brook University. I study the evolution of higher cognition, learning, habit formation, and decision-making in mammals by the application of phylogenetic comparative methods. As a young science communicator, my mission is to provide high-quality and vetted information in a sophisticated, straightforward, and appealing format.
