Causes of aggressive behavior found?

Here's an interesting juxtaposition of stories about causes of aggressive behavior in mice.  A story on the BBC web site, reporting on a paper in the Proceedings of the National Academy of Sciences, suggests that the microbiome in the gut of some lab mice is responsible for their adventurousness.   

The teeming trillions of bacteria in the digestive tracts of mice have been shown to affect the animals' brain development and behaviour.

Mice bred in sterile environments without these "gut flora" were seen to be more adventurous and less anxious than mice with normal gut flora.

The authors compared gene expression profiles in the brains of mice raised in the germ free environment with those in the non-sterile environment and found consistent differences in the levels of expression of 50 genes.  The authors conclude "our results suggest that the microbial colonization process initiates signaling mechanisms that affect neuronal circuits involved in motor control and anxiety behavior."

In situ hybridization results showing Grb10 inactivated
 in mouse on right.

In contrast, a paper in Nature, as reported in the New York Times, suggests that altering a specific gene boosts aggressive behavior in mice.  The Times says

For some genes, either the father’s version or the mother’s version is active, but not both. Which version of the gene works is determined before conception, as the sperm and egg are developing, in a process called imprinting. By mimicking that process in the lab, and turning off a gene in mice, scientists have produced a change in social dominance behavior. In laboratory tests, mice with the paternal version of the gene known as Grb10 inactivated were more aggressive in their behavior...

These papers don't necessarily contradict each other, although it doesn't look like Grb10 is one of the 50 genes whose expression level is affected by microbes in the gut.  If both results are real, this suggests that, like many traits, there may be multiple paths to aggressive behavior.  And that there is no single allele 'for' a trait like this.  That wouldn't be a surprise.

On the other hand, either or both results might well be no more than speculation, as many science stories these days.  The amount of basically wild speculation, picked up by the media as if substantial or well-anchored scientifically, continues to be high.  With 24/7 media, and a public (and scientists) hungry for simple stories, reinforces this.

Of course, there is no reason to doubt that anything might affect anything else, so the main point of responsible science is to balance what is found so far with might be found or might be true or correlated with what is found.  If that were more predominant, stories like these, that are certainly interesting, might be more likely to be viewed as science rather than stories.