Healthy development thanks to older siblings

In a new study, a Leipzig-based team of researchers including scientists from the Helmholtz Centre for Environmental Research (UFZ), Leipzig University (UL), the MPI for Evolutionary Anthropology (MPI EVA) and the German Centre for Integrative Biodiversity Research (iDiv) used longitudinal data from the LINA (Lifestyle and environmental factors and their Influence on the Newborn Allergy risk) cohort to test 373 German mother-child pairs, from pregnancy until 10 years of age.

Mothers were asked to fill in three validated questionnaires, to assess their stress levels and their child's behavioural problems. First, the researchers assessed which social and environmental factors were linked to an increase in maternal stress levels during pregnancy, and the long-term consequences of maternal stress on the occurrence of child behavioural problems. Second, the researchers assessed whether the presence of siblings had a positive effect on the occurrence of child behavioural problems, by directly reducing stress levels and increasing children's psychological well-being, or by indirectly buffering the negative consequences of maternal stress.

Prenatal stress can cause behavioural problems in the child

The results of the study demonstrated that socio-environmental stressors, like the lack of sufficient social areas in the neighbourhood, were clearly linked to an increase in maternal stress levels during pregnancy. Moreover, mothers who had experienced high stress levels, like worries, loss of joy or tension, during pregnancy were also more likely to report the occurrence of behavioural problems when their children were 7, 8 or 10 years old. "These results confirm previous findings about the negative impact that even mild forms of prenatal stress might have on child behaviour, even after several years, and highlight the importance of early intervention policies that increase maternal wellbeing and reduce the risks of maternal stress already during pregnancy," explains Federica Amici (UL, MPI-EVA), one of the researchers involved in the project.

On a more positive note, the study also found a lower occurrence of behavioural problems in children with older siblings. "Children who have older brothers or sisters in their households are less likely to develop problems, which suggests that siblings are crucial to promote a healthy child development," explains Gunda Herberth (UFZ), coordinator of the LINA study.

Higher social competence thanks to older siblings?

This study further suggests that the presence of older siblings directly reduced the likelihood of developing behavioral problems, but did not modulate the negative effects of maternal stress on child behaviour. How could older siblings reduce the occurrence of behavioural problems in children? By interacting with their older siblings, children may develop better emotional, perspective taking and problem solving skills, which are linked to higher social competence and emotional understanding. Moreover, the presence of older siblings may provide learning opportunities for parents, who might thus develop different expectations and better parental skills.

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Differences in brain structure between siblings make some more susceptible to developing severe antisocial behavior

Structural differences in the area of the brain responsible for decision making could explain why two siblings living in the same family might differ in their risk of developing the condition conduct disorder.

Psychologists and neuroscientists have long puzzled over why siblings with seemingly the same upbringing and genetic makeup might differ so significantly in terms of their behaviour: how do some young people growing up in families with antisocial or criminal behaviour manage to stay out of trouble?

Researchers at the universities of Bath and Southampton investigated this question by studying different members of the same families -- some with the mental health condition conduct disorder, and some with no behavioural problems.

Conduct disorder is characterised by repetitive patterns of aggressive and antisocial behaviour. It results in substantial personal and financial costs for affected individuals, their families and society in general and is one of the most common reasons for referral to Child and Adolescent Mental Health Services in the UK.

Conduct disorder has a prevalence rate of around 5% among young people aged between 5 and 16, although there is a steep social class gradient: a 2004 survey revealed almost 40% of looked-after children, those who had been abused or on safeguarding registers, had conduct disorder. Despite all this, general awareness of the condition remains low and it is not recognised by many psychologists or psychiatrists.

The new study, published today in the journal Psychological Medicine, sought to understand underlying mechanisms which might determine someone's risk of developing the condition. The international team, including Dr Graeme Fairchild at the University of Bath, conducted MRI brain scans on 41 adolescents with conduct disorder, 24 unaffected siblings (who had a brother or sister with conduct disorder but did not show the condition themselves) and 38 typically developing controls with no family history of conduct disorder.

Their analysis found that young people with conduct disorder and their relatives both displayed structural differences in the brain -- in a part of the brain called the inferior parietal cortex. However, there were also structural changes in the brain that were specific to the conduct disorder group in brain regions responsible for empathy and cognitive control / inhibiting behaviour that were not found in the unaffected siblings.

In addition, the researchers also found changes in the prefrontal cortex, a brain area involved in planning and decision-making, that were specific to the unaffected sibling group -- which may explain why they are protected from showing antisocial behaviour despite growing up with either environmental or genetic risk factors for conduct disorder. Previous work from the same team found that despite differences in antisocial behaviour between siblings, both those with conduct disorder and their unaffected siblings had difficulties in recognising emotional facial expressions.

Dr Graeme Fairchild from the University of Bath's Department of Psychology explains: "Our study aimed to understand the root causes of conduct disorder, specifically what makes members of the same family differ in their antisocial behaviour and are there genetic risk markers for conduct disorder in the brain.

"This is one of the first family-based studies of conduct disorder and it confirms that the brain is important for distinguishing between members of the same family who are at higher risk of developing antisocial or criminal behaviour.

"Interestingly, whilst our previous work showed common impairments between affected and unaffected siblings in recognising facial expressions, this study suggests that key behavioural differences may be determined by small changes in the part of the brain responsible for executive functioning or decision-making. These differences could make some siblings more prone to risky behaviour and should now be a focus of future study."

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Elephants benefit from having older siblings, especially sisters

A study of semi-captive Asian elephants in Myanmar has found that calves benefit from having older sisters more than older brothers. The findings are published in the British Ecological Society's Journal of Animal Ecology.

Researchers at universities in Finland, the UK and Myanmar have found that Asian elephant siblings influence younger offspring from early through to late-life. Being raised with older siblings strongly increased calves' long-term survival compared to not having a sibling, with elder sisters having a bigger impact than elder brothers.

In female elephants, those raised with older sisters had higher long-term survival and reproduced for the first time an average of two years earlier, compared to those with older brothers. Reproducing at an earlier age is generally associated with more offspring over the course of an elephant's lifetime.

In male elephants, those raised with older sisters had lower survival but higher body weight, compared to those with older brothers. This seemingly detrimental effect may be explained by a 'live-fast, die young' strategy, where the positive early increase in body mass could lead to survival costs later in life.

Dr Vérane Berger at the University of Turku and lead author of the study said: "Our research confirms that sibling relationships shape individual lives, particularly in social species, such as the elephants, where cooperative behaviours are essential to the development, survival and reproductive potential of individuals."

The long-term consequences from sibling effects are understudied in long-lived animals. One of the reasons for this is that the logistic challenges of field studies make it hard to investigate effects over an animal's entire lifespan.

In this study, the researchers were able to overcome this barrier by studying a population of government-owned, semi-captive timber elephants in Myanmar, for which extensive life history records are kept.

These elephants are used during the day as riding, transport and draft animals. At night the elephants live unsupervised in forests and can interact and mate with both wild and tame elephants. Calves are raised by their mothers until the age of five when they are trained for work. The Myanmar Timber Enterprise (MTE) imposes regulations on the daily and annual workload of elephants.

Dr Mirkka Lahdenperä at the University of Turku and co-author of the study said: "Because the elephants live in their natural habitats, there are many similarities to wild elephants, such as natural foraging and no assistance in breeding. While there are differences -- in the wild, family groups are probably bigger -- there are more similarities than differences and we could assume that some of the associations found in our study would also hold true for wild elephants. But of course, these should be studied"

The researchers used a large, multi-generational dataset of semi-captive Asian elephants to look at the influence the presence and the sex of elder siblings on the body mass, reproduction, sex, and survival of the next calf. The records contained precise reproductive and longevity information for 2,344 calves born between 1945 and 2018.

As the study was correlational, the influence of external factors outside sibling effects, such as the quality of maternal care and elephants' workload and management, cannot be excluded.

On the next steps for this research project, Dr Berger said: "By collecting more information on the body mass of mothers at birth, we hope to disentangle maternal effects from sibling effects.

"More data will also let us explore the effects of the environment on sibling relationships and go into more detail on the effects siblings have on specific aspects of a younger calf's health, such as immunity, muscular function and hormonal variations.

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