5.11.1 Importance of common environment

Why would you be interested in the common environmental variance? Most important reason is that its size provides insight in the influence of the common environment on the variation in phenotypes observed. This common environment does not have to be shared at the moment of the recording of the phenotype. For example, age at maturation (first oestrus cycle) in female animals may be influenced by the common environment (e.g. shared litter) months or even years earlier. If the common environment was of good quality this may result in an earlier age at maturation.

The benefit of knowing that these joint shared environmental experiences exist is that being able to quantify the variation in effects of those experiences allows to estimate the heritability more accurately. This is because it is difficult to disentangle the effect of the common environment from the genetic component as closely related animals experience the same common environment. Taking the common environment into account when estimating the variance components helps to ‘clean’ the genetic variance from actual environmental influences that related animals have in common. And it also provides insight in the size of the influence of the early environment on the phenotype.

The phenotypic variance, taking into account the common environmental effect, can be written as:

We can define a common environmental factor, representing the proportion of common environmental variance relative to the total phenotypic variance. This is indicated with a c², analogue to the h² for the heritability.