No proof kids of lone parents are less intelligent

"Children brought up by two parents are more intelligent," is the baseless claim on the Mail Online website.

The headline fails to mention that the research the story is based on involved only mice. Not until eight paragraphs into the news story does the Mail reveal this crucial point.

The scientific study involved housing baby mice with either their mother only, with both 'parents' or with their mother and a matched female 'parent'. These baby mice were then subjected to a series of tests designed to assess their development. After the testing, researchers took tissue samples from the brains of the mice.

The researchers found that:

• male mice housed with two parents seemed to have better threat-recognition abilities than those who were raised by a single mouse mum
• female mice housed with two parents seemed to have better motor co-ordination
• being housed with two parents did seem to affect brain development, although the pattern of development differed between male and female mice

Interesting as this is, it is hard to see how it applies to human families. This study cannot be used to conclude that children raised by one parent will have behavioural differences from, or will be less intelligent than, those raised by two parents.

Where did the story come from?

The study was carried out by researchers from the University of Calgary in Canada and was funded by the Canadian Institutes of Health Research and awards from Alberta Innovates Health Solutions.

The study was published in the peer-reviewed scientific journal PLOS one, which is free to read for all on an open-access basis.

The Mail’s story exaggerates the findings of this unusual animal study. Most of the article reads as if the research were directly relevant to humans or carried out in humans. The Mail encourages this idea by illustrating the story with a picture of a couple with their toddler. It is only in the eighth paragraph of the Mail’s report that the fact that the study was in mice is revealed. The paper offers no thoughts about how relevant research on mice is to humans.

However, much of the exaggeration in the Mail’s reporting can be traced back to a press release about the research issued by the University of Calgary.

What kind of research was this?

This was animal research aiming to investigate the effect that early life experiences can have on brain development, emotions and social behaviour.

In particular, the researchers were interested in the theory that low maternal care leads to changes in the area of the brain involved with memory and emotions (the hippocampus). This may then lead to increased stress and increased sensitivity to changes in emotion and mood (emotional reactivity).

They say that previous studies have shown that when pregnant rodents have been exposed to stress the female offspring developed a smaller hippocampus. As the effect was not seen in male offspring this suggested there may be some gender difference.

This study aimed to see whether parental care offered by two rodent parents rather than one had an effect on brain cell development. Further, the researchers wanted to see whether any changes in development had an effect on the behaviour of the offspring, and whether the effect was different in male and in female offspring. 

This study may be of interest to scientists and psychologists, and offers a possible insight into the factors that may influence animal brain development and behaviour. But it is hard to determine if, or how, the results can ever be applied directly to humans.

What did the research involve?

This research involved eight-week-old female and male mice, who were fed a normal diet and housed under 12-hour light/dark conditions. They were allowed to mate freely. Pregnant females were removed and placed in different parental conditions for the duration of pregnancy, through birth and until weaning at 21 days. In total, 269 animals were involved.

The three conditions were:

• maternal-only condition – the offspring were housed with their mother only
• maternal-virgin condition – the offspring were housed with their mother and an age-matched virgin female mouse
• maternal-paternal condition – the offspring were housed with the mated male-female pair

When housed under the three conditions the researchers observed the time that the parent mice spent in parenting behaviours, such as nursing, licking and grooming, and nest building.

When the offspring were weaned at 21 days they were housed with their littermates. They then completed a series of behavioural tasks ranging from least to most stressful. The tasks included:

• different maze tasks, including water mazes
• light-dark tasks (seeing how long mice spent in light and dark compartments when allowed to navigate freely)
• horizontal ladder tests (looking at how well they walked across the differently-spaced rungs of a ladder)
• tests of social preference (looking at interest in exploring different objects that stimulated the senses)
• tests of passive avoidance (of an electric shock)
• tests of fear conditioning (observing their time spent frozen and motionless when they were exposed to different shocks and sounds)

The researchers also examined tissue samples from the brains of the offspring mice to investigate any biological differences in their brain development.

What were the basic results?

Before weaning, the researchers observed that the parenting behaviour of the mother mouse was no different in the three conditions. Nor did the displays of parenting behaviour from the virgin-female and father-mouse differ from each other in those two respective conditions.

When the researchers worked out the average time spent licking and grooming the offspring (a marker of parental attention), the offspring in the two-parent conditions (either maternal-virgin or maternal-parent) received more attention than those in the maternal-only condition.

Overall, they found effects of parenting upon offspring behaviour and brain cell development differed between male and female offspring. In the various tasks, males raised in the two-parent conditions showed more fear conditioning, by displaying more freezing behaviour than males raised in the maternal-only condition. Meanwhile, females raised in the two-parent conditions showed better co-ordination when walking across the ladder than females in the maternal-only condition. The two-parent females also displayed more interest in exploring different objects.

This suggests that being raised in an environment with the biological mother and another adult mouse (male or female), may improve or accelerate some, but not all, developmental skills.

Two-parent care also had more effect on the male mouse brain. Male offspring in both the two-parent conditions had more growth of cells in a certain part of the hippocampus (the dentate gyrus). Parenting experience didn’t seem to have an effect on the hippocampus of the female offspring. However, females raised under the two-parent conditions did show greater proliferation of the white matter (the nerve fibres) of the brain.

How did the researchers interpret the results?

The researchers say that early life experiences can have an effect on brain development and behaviour, and that this persists through life. Male and female offspring appear to be affected in different ways.

They note in the abstract of their published research article (but do not describe in detail in the main research methods or results) that some of the brain development and behavioural advantages due to two-parent upbringing can stay with the mice throughout life and can be transmitted to the next generation.

Conclusion

This animal study suggests that male and female mice raised in two-parent conditions display differences in their brain cell development and behaviour compared with mice raised with only their mother.

While there are similarities between mice and men, it would be a mistake to assume that the findings in this mice study can be applied to humans. There are many important differences between the parenting of mice and people, and many differences in biology and social development that make it impossible to translate these findings to people.

Nonetheless, this study will be of interest to scientists and psychologists and offers a possible insight into the factors that may influence animal brain development and behaviour. Future research can build on these findings.

It should not be assumed from this study that children raised by one parent will have behavioural differences from those raised by two parents. The Mail Online also mistakenly suggests that this study supports the idea that children brought up by two parents are more intelligent. Apart from the fact that it was a rodent study, the study did not examine the ‘intelligence’ of the mice, so this assumption is groundless.

The main differences observed were that male mice from two-parent families seemed to freeze more when exposed to a perceived threat, and that female mice from two-parent families were more interested in exploring objects and better at walking over a ladder. It is a distortion of the evidence to conclude from this that children from two-parent families are more intelligent.

If you are shocked by the reporting of this study, first by the University of Calgary’s press office (or to be specific, its Hotchkiss Brain Institute) and then by the Mail Online, you may want to read about a study published in 2012. It found that half of all health reporting is subject to some sort of ‘spin’ with researchers and academic press offices shouldering a large proportion of the blame.