Genes required for learning, memory, aggression and other complex behaviours originated around 650 million years ago, says a study published in the journal Nature Communications.
The researchers from the University of Leicester, UK, said that monoamines such as serotonin, dopamine and adrenaline that act as neurotransmitters in the nervous system play a role in complex behaviour and functions such as learning and memory, and processes such as sleep and feeding.
The researchers reconstructed the evolutionary history of these genes using computational methods, and showed that most of the genes involved in monoamine production, modulation, and reception originated in the bilaterian stem group.
Bilaterians are a group of animals with bilateral symmetry as an embryo, i.e. with a left and a right side that are mirror images of each other. This discovery suggests that the monoaminergic system evolved to the Cryogenian/Ediacaran boundary, about 650-600 million years ago.
The researchers suggest that this new way to modulate neuronal circuits might have played a role in the Cambrian Explosion known as the Big Bang, which gave rise to the largest diversification of life for most major living animal groups today by providing flexibility of the neural circuits to facilitate the interaction with the environment.
The discovery will open new research avenues to help clarify the origin of complex behaviours, and if the same neurons modulate reward, addiction, aggression, feeding, and sleep, the researchers added.