Science cover study suggests vertebrate ancestors had complex brains 500 million years ago

What did the ancestor of all vertebrates – including humans – look like?

A Chinese-led study featured on the cover of Science suggests that one important clue may lie in the brain of a lamprey, an ancient jawless fish often described as a living fossil. The research found that the common ancestor of vertebrates may already have possessed a surprisingly complex brain around 500 million years ago.

The study was conducted by researchers from BGI Research, the Kunming Institute of Zoology under the Chinese Academy of Sciences, and Liaoning Normal University.

The study focused on the Far Eastern brook lamprey (Lethenteron reissneri), a species whose ancestors diverged from those of modern fish, birds, mammals and humans hundreds of millions of years ago. Because its basic body plan has changed relatively little since then, scientists regard it as one of the best living models for studying the origins of vertebrate brains.

Using spatial transcriptomics and single-nucleus RNA sequencing, the team created the first three-dimensional single-cell atlas of a lamprey brain, analyzing more than 460,000 cells across 14 major brain regions.

The researchers found that the vertebrate common ancestor already had a highly regionalized brain, with distinct regions specialized for different functions. Many of the basic brain structures seen in vertebrates today appear to have been established far earlier than previously understood.

The findings challenge the idea that complex vertebrate brains gradually evolved from a simple ancestral nervous system. Instead, they suggest that much of the blueprint for modern vertebrate brains was already in place half a billion years ago.

By comparing lampreys with other vertebrates, the researchers also found evidence that brain evolution was driven in part by increasing neuronal specialization. Early vertebrates appear to have relied more heavily on broadly functioning nerve cells, while later vertebrate groups developed more specialized neurons with distinct roles.

The findings provide new insight into how vertebrate brains became more diverse over time and offer a clearer picture of how the complex brains seen in modern animals – including humans – evolved from their ancient ancestors.

(Cover via VCG)