Personality differences from day one after birth despite identical genes and identical environment
Amazon mollys are natural clones of their mother, therefore genetically identical. A perfect model for twin studies. Credit: David Bierbach

Current knowledge shows that personality is determined by genetics and environment. Is it possible for genetically identical people to grow up under the same conditions? Twin studies have been unable to answer the fundamental question.

For the first time, a group of researchers from the IGB and the Cluster of excellence Science of Intelligence have shown that genetically identical individuals already differ in their character traits on the first day of life in naturally clonal fish. The study was published in a peer reviewed journal.

It has been thought that differences in the genome and environment play a role in the formation of personality. There have been no experimental approaches to completely rule out these factors. Behavioral individuality emerges without any genetic or environmental variation in our experiment.

Max Wolf and his team have shown that animals with the same genetic material and environment have different personality characteristics from the first day of life. They studied the behavior of the Amazon molly. The fish reproduce clonally. The offspring are clones of the mother. There is no care for the children. It is possible to keep them individually under the same conditions from the beginning.

The first 10 weeks of the Amazon molly's lives were recorded with the help of a high-resolution tracking system.

Personality differences from day one after birth despite identical genes and identical environment
Individuality is present at day one after birth and is not explained by differences in maternal identity or body size. Repeatability of median swimming speed at hourly intervals on the first day after birth (A); each line represents one individual (N = 26). Maternal identity (B) did not explain variation in swimming speeds among individuals. Small and large points indicate the hourly (i.e. 11 data points per individual) and daily median swimming speeds, respectively, of individuals from each mother on day one after birth. Behavior on day one after birth (C) was not related to an individual's total length on their first day of life. Small and large points indicate hourly and daily median swimming speeds for each individual respectively; gray lines indicate posterior estimates for the effects of body size on behavior. Throughout, lines and points are colored according to the individual's behavior in hour one on day one (yellow represents higher swimming speeds; purple indicates lower swimming speeds). Credit: Nature Communications (2022). DOI: 10.1038/s41467-022-34113-y

Day one after birth, individual personality.

The first day after birth is when strong behavioral individualities are present. The differences in individual behavioral patterns persisted throughout the ten weeks of the experiment and even gradually increased, according to one of the first authors of the study.

In a previous study done by the team of David and Max Wolf, they showed that behavioral individuality emerges despite identical genes and the same environment. The researchers were able to show that this behavioral individuality is already present on the first day of life.

"This is the first experimental evidence that individuality in later life can be strongly shaped by pre-birth factors, such as the nutrition in the womb or other maternal effects, epigenetics and pre- birth development," said David Bierbach.

The emergence and development of behavioral individuality in fish.

Journal information: Nature Communications