Personality
Nematodes (roundworms) occupy every part of the world’s oceans and terrestrial and aquatic landmasses, numbering perhaps 1 million species. The temperate soil-living species Caenorhabditis elegans has a nervous system of only 302 neurons, yet its neuromodulators regulate consistent variation between individual worms in their patterns of roaming and dwelling behaviour1. This non-genetic signature of personality may change with development stage or persist throughout development.
Humans express complex personalities, commonly framed by five continuous dimensions: openness to experience, conscientiousness, extraversion, agreeableness, neuroticism. Within these dimensions, patterns of self-reported behaviour tend to cluster around four personality types: self-centred (more likely in younger people), reserved, role-model (more frequently in older people), and average (in-between and overlapping the other three clusters)2, 3.
As we age, we grow out of one dominant personality type into another, depicted since antiquity as the seasons of life and caricatured by Shakespeare’s Jaques in As You Like It (1623), entwining life with theatre: “All the world’s a stage, and all the men and women merely players …”
For humans, as for nematodes, it remains unclear what personality really is. Genes and environment likely constitute the distal causes of a personality that is instantiated in the brain and expressed in individually distinct behaviours4. Without personality, we would have no personhood. We would be as we become at the seventh and final age in Jaques’ soliloquy – “mere oblivion; sans teeth, sans eyes, sans taste, sans everything.”