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An Origin Story – Brain Evolution in Rodents: What did our ancestor’s brain look like?

This piece belongs to my blog series at https://edingeoslife.com where I discuss the seminars I attended hosted by the University of Edinburgh. The first blog entry can be found at: Why All students, from All years, from All subjects should attend Seminars.

Title of the Talk: Brain Evolution in rodents: What did our ancestor’s brain look like?

Speaker: Dr Ornella Bertrand

Humans and Squirrels are related

Dr. Bertrand’s talk and research aims to understand the evolution of rodent brains from the Euarchontoglires family as they share a common ancestor with us, mankind. If we can understand how brains changed in other species genetically close to us, we can gain a greater insight about our own brain’s evolution. This would permit us to gain a greater insight into the inner workings of our own brains.

The main question about the past of our brain is: How did brain diversity emerge? And Why did it emerge?

In order to understand the processes bringing our brain to life, Dr. Bertrand took fossils from the Euarchontoglires family and attempted to recreate their brain in order to measure their overall size and the sizes of specific areas. Than she compared brain sizes and specifically the size difference between the different neocortexes with the past lifestyles of the creatures (based on fossil evidence and modern ancestors). She gained the measurements by using a micro-CT scanner, latex and plaster, getting the endocast of the brain of each animal, revealing their past shapes and sizes.  She fed the data into a computer program allowing an understanding of how the skulls changed over time to accommodate different brains and how certain elements of the brain changed due to environmental pressures.

CT scan of a young Prosciurus relictus

Her findings were very interesting and revealed a lot about long term brain plasticity. As intelligence goes up in an animal, the brain size increases compared to the body mass, however it can decrease if the animal does not require intelligence for survival.

The living environment is one of the largest factors influencing brain development. The ancestors of squirrels and moles both belong to the Euarchontoglires family, yet they turned out to be completely different. The squirrel lives up in the trees and is more intelligent compared to the mole which spends most of its life underground. This can be observed of their diet too. The diet of the squirrel is much more diverse compared to the mole’s. The two creatures in their group changed completely (including their brains) when they happened to live in two different environments.  This effect was the most visible on their neocortex (the section of the brain responsible for sight and hearing in mammals). The neocortex of the ancestors of the modern squirrel grew as they moved up into the trees. In order to survive the ancestor needed extra brain power for complex locomotion and navigation between the trees. The exact opposite happened for the ancestor of the mole. It had no reason to develop a good eyesight so along with its eyes the overall brain and the neocortex shrunk.

The changing size of the neocortex

The squirrels with their larger brains became good generalists, while the moles only adapted to a certain set of conditions and lifestyle.

Dr. Bertrand looked at other reasons for a decrease in brain size. The two other major factors were lack of predators and human domestication.

Her continuing research will aim to document the further members of Euarchontoglires from the fossil record in more detail. She wants to learn more about mammal evolution after the extinction of the dinosaurs. The aim would be to see how placental diversification happened. Did the diversification of mammals explode in rate or did it steadily increase after the K-T extinction? She aims to apply her current research techniques on later mammals to mammals right after the K-T extinction event. How did the post-dinosaur environment effect their brain growth? Did it cause an acceleration in their intelligence?

Why this is a Philosophical matter not just a Palaeontological one

In the pre-Darwin era the origin of mankind was simple. Man created by God, ever perfect, only corrupted by original sin. Evolution threw that idea back into chaos. The pedestal on which man stood as infinitely above raw nature, a creature that is wise and not subject to the whims of natural forces, crumbled. Morality itself was questioned. Were we creatures capable of free choice? Did our actions follow our knowledge of Good and Evil? Or were they a consequence of the impulses of natural selection, where the weak had to die and the strong strive to dominate all? Were we just another entry on the long line of the evolutionary story where we were destined to be swept away by the sandstorm of time?

These are questions that since the 19th century have bothered peasant and king. Some rejected the ideas of Darwin as fanciful and nothing else. Others while deeply agreeing with Darwin chose to separate the two, treating mankind as the next step. As a civilisation builder, who while originated from apes, have moved beyond carnal desires, using science and philosophy to light a candle in the dark. A being that managed to be that conscious point of the universe, casting the rules of evolution aside.

Others took the idea of evolution to their very heart: Nature is a dangerous game and everybody is a player, subject to the same harsh rules. If you loose (which you must not) you die. This mentality was taken up by the highest echelons of power and applied on a scale of civilisations. Ultimately this lead to the rise of social Darwinism internally of civilisation and externally. A lot of European Empires based their conquests on those ideas. The world was a free for all and if you didn’t dominate, you were crushed by some other Empire joining the ranks of Ancient Egypt, Rome or the Aztecs. This view of the world ultimately ended in the horrors of the World Wars.

However after the levelled cities of Europe and the burnt out islands of the Pacific, the pendulum swung the other way. Mankind invented and discovered so much in the past 400-500 years. No way we were just machines of nature acting out impulses to propagate the species. We were (and are) thinkers that are capable to dream up and create abstract systems. We built civilisations and when they burnt down, we rebuilt them. Therefore despite a divided world of East and West both parties came to the same conclusions: Evolution while interesting to study is not a determiner of the future. The force that created mankind must be shunned and controlled in order for mankind to have a hope at a future. This was to be seen in Global Politics. The West had embraced Capitalism and Liberalism, ideas that while fed into evolution, stand contrary to the basic rules of natural selection. The East embraced Socialism and Communism, another set of ideas that emphasised mind and human will over Nature. The idea of Evolution completely changed the way we look at the world and the way we look at our societies.

Evolution? – Soviet poster against the Nuclear Arms race

Further Reading

Virtual endocasts of fossil Sciuroidea: brain size reduction in the evolution of fossoriality

Virtual endocasts of Eocene Paramys (Paramyinae): oldest endocranial record for Rodentia and early brain evolution in Euarchontoglires