The first experimental proof that brain areas can change independently of one another during cognitive evolution has been revealed by researchers at Stockholm University. This so-called mosaic brain evolution was empirically confirmed in a four-generation artificial selection experiment with guppies (Poecilia reticulata), where telencephalon size (but not other regions) differed by 10%.
The discoveries could have a big impact on how we think about cognitive evolution in other animals like monkeys and humans. According to the findings, brain evolution can take the shape of alterations in individual brain regions in a mosaic pattern, with separate sections evolving independently.
The mammalian brain is made up of several functionally separate systems. As a result, it’s reasonable to assume that natural selection on specific behavioral capacities would have resulted in significant changes in the systems that mediate such capacities.
However, it has been suggested that developmental restrictions stifled mosaic evolution, resulting in changes in the size of particular brain components. The researchers discovered that when the telencephalon, or Cerebrum, is subjected to intense artificial selection, its relative size changes swiftly and in an autonomous manner.
“The finding has large implication for our understanding of how vertebrate brains evolve and can help us explain even human brain evolution. For instance, it is possible that cognitive demands in the environment led to gradual evolutionary changes in the size of the neocortex towards the large neocortex in humans,” says Niclas Kolm, professor at the Department of Zoology at Stockholm University and lead principal investigator on the project.
Stephanie Fong, who recently defended her Ph.D. thesis on the project, conducted the experiment with guppies using artificial selection.
The finding has large implications for our understanding of how vertebrate brains evolve and can help us explain even human brain evolution. For instance, it is possible that cognitive demands in the environment led to gradual evolutionary changes in the size of the neocortex towards the large neocortex in humans.
Niclas Kolm
Stephanie discovered significant changes in telencephalon size in both males and females after four generations of selection on relative telencephalon volume compared to the rest of the brain, a three-year endeavor that needed nearly 2000 aquaria and hundreds of brain dissections by Stephanie. However, no substantial changes were observed in other areas, supporting the mosaic brain concept.
According to the mosaic brain evolution concept, there are selective factors that affect certain portions of the brain, such as cognitive demands from the environment to capture food or find mates, but these adaptive responses do not involve other parts of the brain when they occur. As a result, distinct brain regions can evolve in a “mosaic” pattern, in different ways and at varying rates, saving energy compared to modifying the whole brain.
“The study is unique because it demonstrates that targeted selection on a single region can quickly increase and decrease its size without strong correlated changes in other regions,” says Stephanie Fong.
Neuroimaging studies have recently offered in vivo evidence regarding the neuroanatomical correlates of energy intake regulation. However, the integration of neural and hormonal signals that drive eating behavior requires the temporal orchestration of such systems.
In terms of the distinct parts of the vertebrate brain, the general arrangement of the vertebrate brain is impressively preserved. However, there is a huge difference in size between species in different places. And this size difference could have been created by mosaic brain evolution, which would have far-reaching cognitive implications.
“The study suggests that strong selection can independently change separate brain regions and thus potentially yield cost-efficient neural responses to very specific cognitive demands from the environment. The next important step, and we already have publications on the way, is to investigate the functional consequences of these fast evolutionary changes in relative telencephalon size,” says Niclas Kolm.
