Inheritance of Environmental Influences? April 18, 2007Posted by Johan in Behavioural Genetics.
One of the basic tenets of the theory of evolution through natural selection is that learned behaviours are not inherited. A recent study by Lindqvist et al (2007) suggests that this rule has exceptions.
Lindqvist et al (2007) raised two breeds of chickens under stressful or non-stressful conditions. Stress was induced by randomly turning on and off the light, which is very disturbing to chickens since many of their behaviours are tied to the day-night cycle (e.g., they do not feed in darkness). From the eggs produced by these two groups, a sample was raised under identical, non-stressful conditions.
To test the effects of the stressful environment, the parents in the two groups and their offspring performed a maze learning test. Additionally, the offspring were tested for their ability to compete with each other for access to food.
The behavioural results indicated that stressed chickens in the parental generation needed more trials to solve the maze test. This in itself is not surprising – it merely shows that the stressful environment did affect the parental generation. Among the offspring, there was no significant difference between chickens with stressed and nonstressed parents. However, with some statistical trickery (testing differences in the cumulative proportion of birds that solved the test after each trial), a significant difference emerged for one of the chicken breeds. No significant differences emerged for the competition task, or for the other breed.
So it would seem that for one breed, the stress carried over, presumably due to changes in gene expression carrying over to the next generation. Lindqvist et al (2007) carried out some genetic analyses to investigate this possibility, and appear to have found some evidence to support this. Unfortunately, my understanding of genetics is not strong enough to give you a decent review of this part of the paper.
This study has been cited in more than one Swedish newspaper as evidence that “disproves” Darwin’s theory. I very much doubt that. First, unexpected results from a single study need to be confirmed. Secondly, the significant difference between the two groups that this paper hinges on had to be literally squeezed out of the data.
Given the interpretation that Lindqvist et al (2007) give their data (ie that changes in gene expression were transmitted across generations), I see a problem with their design: The stressful environment may have damaged the hens’ eggs or general egg-production. The eggs were only taken out of the stressful environment once they had been laid, of course, so while the chicken were then raised in a non-stressful environment, the prenatal environment may not have been equivalent for the two groups. However, one finding that speaks against this criticism is the lack of a significant difference between the hatchability of the eggs from the two groups. Any negative changes in the prenatal environment should affect hatchability, presumably.
I find this paper fascinating, but at the same time it is outside my subject area, so I want to end with a disclaimer: I don’t know as much about this subject as I do about my normal topics. If someone with a better grasp of genetics blogs this story I’ll be sure to update this post with links.
Lindqvist, C., Janczak, A.M., Nätt, D., Baranowska, I., Lindqvist, N., Wichman, A., Lundeberg, J., Lindberg, J., Torjesen, P.A., & Jensen, P. (2007). Transmission of Stress-Induced Learning Impairment and Associated Brain Gene Expression from Parents to Offspring in Chickens. PLoS ONE, 4, 1-7.