A Big Birthday, Big Brains and the Link between Facebook and Mormon Great Trek Parties
Nisha Doshi and Bex Walton
Last week, in celebration of the 200th anniversary of the birth of Charles Darwin, a number of UK-based PLoSsers made the trek to London’s Natural History Museum to attend the annual celebration of Darwin’s Birthday Party, held annually by the Centre for Ecology and Evolution (CEE) since 1994. The CEE is an organisation set up to foster communication between ecologists and evolutionary biologists working at various institutions across London. The CEE's co-director Sandy Knapp was our host for the afternoon.
Since the first Birthday Party, 15 years ago, a variety of topics have been covered in the lectures, from evolution in the Cambrian to the origins of biodiversity. This year’s topic was the evolution of the brain, “Organs of extreme perfection and complication,” with Professor Robert Barton of Durham University, and Professor Robin Dunbar of the University of Oxford, both expressing their ideas on this fascinating theme. Barton, whose research interests (psychology, zoology and anthropology, mainly) Knapp described as “weird and nefarious”, addressed the question of why primates have big brains. Dunbar then went on to discuss the evolution of the monogamous brain.
“Sleep is good for you – so feel free to fall asleep during this lecture – and I’ve included something to offend everyone,” began Robert Barton, the first speaker of this year’s Darwin’s Birthday Party. Immediately, we were informed that there is no such thing as the brain, and that Darwin would undoubtedly be disappointed by the state of today’s neuroscience. The need to improve the relationship between neuroscience and evolutionary biology and the importance of studying species differences between brain structures, instead of the brain as a unitary phenomenon, were threads which ran throughout Barton’s fast-moving and engaging lecture, which mapped neural specialisations from goldfish and glass knifefish to monkeys and great apes.
Since brains don’t fossilise well, their evolution cannot be studied directly but is instead investigated by means of phylogenetic comparative analysis of brain size and structure in living species, explained Barton. In contrast with spandrelism – the theory that variations in species’ brain size are merely side-effects resulting from allometric scaling – Barton outlined his belief that large primate brain sizes are adaptations resulting from visual specialisation: large frontally-directed eyes, high acuity and stereovision are all computationally costly. In addition, Barton criticised researchers’ tendencies to focus on the neocortex, arguing that the cerebellum also has an important role to play in visual manipulation in the great apes and proposing that linkages between neural systems in the neocortex and cerebellum are vital for both production and social perception of behaviour. Brain evolution is a messy story, he concluded.
But the second lecture, given by Robin Dunbar of Oxford University, presented a simpler picture: as primate group size increases, brain size increases. Furthermore, monogamy has selected for large brain size as long-term pair-bonding is computationally costly, due to the need for extremely careful mate choice and a lifelong need to schedule behaviour to achieve synchronised co-ordination of behaviour. It would be no use one member of the pair spending too much time in pub if the other then had to abandon the nest to find food, Dunbar explained. Extrapolating from the correlation between group size and brain size, Dunbar has come up with a magic number for human group size: 150. This number, he says, fits a wide range of human group-types, from Neolithic settlements to church congregations, 18th-century villages, research sub-disciplines, Mormon Great Trek parties and Christmas card networks. Except in Kent, apparently, where village sizes averages at 100, he says.
Moreover, Dunbar showed that the number of close friends a person has correlates with the size of their dorsal prefrontal cortex. He suggested that nurture has an effect here, too: the larger the family you grow up in, the faster this area of your brain develops and thus the larger the number of close relationships you are likely to be able to support as an adult. Not that this implies that promiscuity is associated with large brain size, he emphasised – the relationship between monogamy and encephalisation still holds. Lastly, do social networking sites impact on the relationship between neural structures and social interaction? Not so, explained Dunbar – the multitudes of people we all seem to add on Facebook have no effect on the magic number and, on the whole, we still only interact with an average of 150 friends.
Supporting Dunbar’s theory, approximately 150 of us gathered after the lectures—behind the scenes at the museum, as it were—to raise a glass to Darwin and to discuss some of the ideas we had heard more informally. And to compare the number of Facebook friends we all have, of course.