The field of research into personality and behavioural syndromes in animals has blossomed over the past few decades. With ample evidence for it’s existence, biologists have begun to consider its evolution; what is the adaptive benefit of personality? How are multiple personality types maintained in a population? Why do personalities exist when they sometimes result in maladaptive responses?
All these questions, and any evolutionary questions we might care to ask, make the assumption that personality is heritable. Without heritability, personality cannot be passed from generation to generation, and cannot be subject to natural selection. There is now plenty of evidence for high heritability of many personality traits in animals, although there is also an important influence of the environment too. Heritabilities estimates vary, from 0.22 – 0.61 in wild great tits, 0.32 in social spiders, 0.54 – 0.66 in humans and 0.2 – 0.8 in dumpling squid. These genetic influences may in part be reflected in brain morphology; one study in humans found differences in brain structure relating to neuroticism, conscientiousness, and extraversion. More neurotic people have a smaller total brain volume and a smaller frontotemporal surface area, whilst extraverts have a thinner inferior frontal gyrus.