According to current knowledge, personality is determined by genetic predisposition and environmental influences. If genetically identical individuals grow up under identical conditions, are these individuals completely identical? Scientists are trying to answer this Q.

A team of researchers  has now shown for the first time in naturally clonal fish that genetically identical individuals already differ in their character traits on the first day of life and that these early character differences significantly shape the behavior of the animals into adulthood. The study was published in the journal Nature Communications.

Until now, it has been assumed that differences in the genome and environmental conditions play the decisive role in the formation of differences in personality. But there have been no experimental approaches to completely rule out these two factors. A new experiment shows how behavioural individuality emerges in the absence of any genetic or environmental variation.

These researchers  have shown that animals with identical genetic material and identical environmental conditions develop different personality traits from the first day of life, which continue to strengthen and stabilize throughout their lives. The researchers studied the behavior of the Amazon molly (Poecilia formosa). These fish naturally reproduce clonally. The offspring are therefore copies of the mother and thus genetically identical. There is also no brood care. They can therefore be kept individually under identical conditions from day one.

With the help of a high-resolution tracking system, the behaviour of the Amazon molly, which were kept in identical environments immediately after birth, was recorded over the first 10 weeks of their lives.

The researchers found that strong behavioural individualities are already present on the first day after birth—for example, the animals differ systematically in their activity patterns. These differences in individual behavioral patterns persisted throughout the ten weeks of the experiment and even gradually increased.

This is the first experimental evidence that individuality in later life can be strongly shaped by prenatal factors, such as the nourishment in the womb or other maternal effects, epigenetics and pre-birth developmental stochasticity. 

Kate L. Laskowski et al, The emergence and development of behavioral individuality in clonal fish, Nature Communications (2022). DOI: 10.1038/s41467-022-34113-y

Same genes, same environment, different personality: Is individuality unavoidable?

David Bierbach et al. Behavioural individuality in clonal fish arises despite near-identical rearing conditions, Nature Communications (2017). DOI: 10.1038/ncomms15361