’A large brain can’t be equated with high intelligence’

Evolutionary scientist Marc de Lussanet talks about the evolution of this high-performance organ

An evolutionary scenario: a primeval fish has turned onto its side in order to h
An evolutionary scenario: a primeval fish has turned onto its side in order to hide on the seabed. Its mouth and fins have compensated for the movement in a clockwise direction from the fish’s view, with the eyes and the nostrils going in the opposite direction. © Almut Krömer
Anyone who expects research to be carried out at the Institute of Sports Science into training, teaching, movement or psychology is quite right. However, anyone who thinks that an evolutionary scientist doesn’t belong there is mistaken. One of the things that Dr. Marc de Lussanet de la Sablonière researches into in the field of kinesiology is the evolution of the brain and of the body. In this interview with Hanna Dieckmann he talks about the advantages and disadvantages of wrinkled and smooth brains, as well as why the human body is structured both symmetrically and asymmetrically, and why such knowledge interests kinesiologists.

One of the focuses of your research is the evolution and development of the brain. You yourself raised the question of why the human brain is wrinkled, just like a walnut. Is there a simple answer to that?

No, there isn’t. Mammals - and only the larger ones - are alone in having a wrinkled cerebrum. The larger the mammal, the more wrinkled the brain. Very large brains, such as in humans, have much more strongly specialised areas than small brains such as are found in mice, and the computing capacity is located in these local networks in the grey matter. This is why a large, very wrinkled brain can, on the one hand, be an advantage. However, this goes hand in hand with a relatively poor ’internal network’: areas farther away from one another, for example the left and the right sides of the brain, are, relatively speaking, much less well connected than is the case in mice.

So the fact that humans feel superior because of the structure of their brain needs to be viewed with some caution?
Seeing humans as the "crown of creation" is an entirely outdated construct - one that has, moreover, been disproved and which, to my knowledge, was influenced by theology and ideology. On top of that, it is also a dangerous view to hold because racist and other ideologies were derived from it, for example the idea that humans can do whatever they like to and with creation.

There is a study which says that over 200 million years ago there were mammals which had furrows in the surface of their brain. Some species lost these in the course of evolution. Why is having a wrinkled brain an advantage for humans, from an evolutionary point of view, but not for other animals?
Interesting! According to my theory, the wrinkled brain would not in itself be an advantage. It is actually more of a disadvantage as it restricts an efficient flow of information. Ravens, for example, which are considered to be especially intelligent, have a small, smooth cerebrum. In general, a bird’s cerebrum is smooth, which means that the connections between the regions of the brain are much shorter. I assume that is a big advantage and, as a result, an important factor in the outstanding cognitive abilities of many species of birds.

There is a loose connection between the size of the brain and the size of the body, with predators typically having a larger brain than herbivorous creatures of the same size.

So the size of the brain important then after all?
It’s certainly important for thinking ability - but it’s only one factor among many. Conversely, a large brain can’t be equated with high intelligence. It is assumed that a whale’s brain is large so that it can regulate its own heat. In other words, a significant percentage of cells are not neurons but cells which produce heat - so-called astrocytes.

You’re also researching into so-called contralaterality, i.e. that the right forebrain mostly represents the left side of the body and vice-versa...
A rotation along the body’s axis can be found in all related groups of vertebrates, and so it must have arisen at a very early stage, even before the "Cambrian explosion" 500 million years ago which gave rise to all the species of animal we know today. This makes the question of evolution very difficult and speculative - because we know almost nothing about this period. My own speculation would be that an earlier ancestor had swimming larvae which settled on the seabed and fed off whatever fell down from above. In order to make eating easier, they turned through 90 degrees onto the left side - which led to an evolutionary advantage of an asymmetrical development and, ultimately, to an axial twist. But that’s pure speculation.

So there is no evidence for how contralaterality came about?

Exactly. However, in line with the theory of axial twist I was able to show that contralaterality is a by-product of the counter-rotation along the body’s axis - without any evolutionary advantage of its own. This means that contralaterality still exists today because the development process of vertebrate embryos is so complicated and fine-tuned. There are malfunctions in the development which can probably be attributed to faults in the axial twist. These always cause severe disabilities, for example massive deformities of the heart or even embryos which cannot survive.

Let’s come back again to the origins of contralaterality. Can you explain it a little more?
The rotation might for example have enabled the animal to hide on the seabed like a flounder. However, the bilateral symmetrical arrangement of the external body parts - with the eyes coming into being on the left and the right sides in the head, and the fins developing on the right and the left sides of the body - would have been lost as a result of a simple rotation. In order to restore the symmetrical arrangement, what happened was that in the course of evolution individual parts of the body shifted - some anti-clockwise, some clockwise. The eyes, the nostrils and the forebrain shifted accordingly in the direction of the original rotation, while areas of the brain and the body located farther towards the tail shifted in the opposite direction. In this way, some neural pathways crossed between the areas of the body - with the development for example of the optic chiasma, the crossing of the optic nerves. Imagine it being like wringing out a wet flannel: you twist the two ends in opposite directions.

You work in the field of movement science: why is knowledge about contralaterality, asymmetries and evolution of interest for your field of work?
Ever since I studied biology in Wageningen, in the Netherlands, I’ve been interested in evolution. In the past, an incorrect, superficial understanding of the theory of evolution led to a lot of wrong conceptions in a range of scientific disciplines. What we can say, though, is that the symmetrical structure of the spine with its muscles and fasciae is obviously important for a healthy, stable back. There are indications that scoliosis (an irregular curvature of the spine) arises when the thoracic and the lumbar vertebrae grow asymmetrically. On average the vertebral bodies are asymmetrical, as is implied by the theory of axial torsion I mentioned before. In some people, however, this asymmetry is too pronounced. In connection with strong growth, this can easily lead to mechanical instability.

So we humans are both asymmetrical and symmetrical - pretty confusing...
Strange as it may sound, the effect of 180-degree rotation during an embyro’s development is to make the body symmetrical again. If the rotation is not completed - in other words, if it is less than 180 degrees - this leads to asymmetries. What I think is confusing for the non-specialist is that a fully grown body appears to be symmetrical when seen from the outside - despite the fact that the front of the head with the cerebrum and the face has normally been rotated through 180 degrees.

Where in particular do biology and sports science meet in your research?
During my studies I first worked on biomechanics and kinesiology in seahorses and related fish. In their own way, they too can be very sporty. For me, humans are a further species which offer excellent opportunities for research because they can learn and can communicate. They display a lot of complex, highly interesting behavioural patterns. Of course, another reason I find humans interesting is that I’m one too.

Literature on this topic:

Marc H. E. de Lussanet. Opposite asymmetries of face and trunk and of kissing and hugging, as predicted by the axial twist hypothesis. PeerJ, 7:e7096, 2019. doi: 10.7717/peerj.7096.

Marc H. E. de Lussanet. Comment on "Cortical folding scales universally with surface area and thickness, not number of neurons". Science, 351(6275):825, 2016. aad0127.