Study Shows That Genetically Identical Fish Can Have Lasting Behavioral Differences.

 This is an interesting study:

The Emergence and Development of Behavioral Individuality in Clonal Fish

 The study monitored the “behavior” of a specific clonal strain of a species of fish (Poecilia Formosa). They noted that, despite the fish all being genetically identical, they exhibited varying behavior (swimming speed, how active, etc.). 

Our findings show that substantial behavioral individuality is already present at the very first day of life after birth among genetically identical individuals, suggesting that pre-birth processes like pre-birth developmental stochasticity and/or maternal effects might play considerably more important roles in shaping behavioral individuality than commonly thought.

This variability only strengthened as the fish got older. From my perspective, the interesting thing is the extent to which this suggests behavior is not that defined by genetics, at least in fish. One might assume that this would extend to the more complex behaviors of humans, though, which begs the question as to how much influence genetic variants can have in human behavior for even one generation, much less be identified in genetically different individuals who merely share some common genetic variants. The math just doesn’t seem to be there for high heritability, if there is any heritability at all.

It would be interesting to see this experiment repeated with genetically varied fish and see if there is any more variation in their behavior (assuming they are physically the same size and shape, etc.) than you see with genetically identical fish. My guess is that it would be minimal.