Neurotic women are more fertile and have 12 per cent more babies than their laid-back female counterparts, according to new research.
The study investigated the link between personality traits and fertility in populations with traditionally high birth rates.
Boffins found women with higher levels of neuroticism and more extrovert men are likely to have a significantly higher number of children.
But researchers also found a link between maternal personality traits and their offspring’s physical condition.
Neurotic women are more likely to have malnourished children with decreased body mass index (BMI), suggesting their negative personality trait carries a cost for families.
The month-long personality study was carried out among around 65 families in four villages in rural Senegal.
Lead researcher Dr Virpi Lummaa, from the University of Sheffield, said it was the first time such a study had been done in a developing country.
Previous work on personality traits and birth rates in modern Western countries revealed neurotic women typically had fewer children.
The unexpected results from Senegal could explain why the genetically inherited trait of neuroticism has not died out as a result of evolution.
But boffins are still trying to figure out exactly why neuroticism bucks the trend and results in larger families in developing countries.
Dr Lummaa, from the Department of Animal and Plant Sciences, said higher sex drive among neurotic women could be a possible cause.
She said: ”We can only speculate about the cause of these results, a lot more work needs to be done in this field.
”Women who are highly neurotic tend to have more short term sexual partners suggesting a link between their sex drive and personality trait.
”In the type of society where contraception is not common that could explain why these women have more children.
”For a long time what has been puzzling about neuroticism is that it is related to bad health, dying younger and less kids.
”There was nothing positive related to it and as a heritable trait you would have predicted it would disappear from the population.
”That is why we wanted to look for reproductive outcomes in other types of society.”
Researchers translated around 30 questions based on the Big Five personality dimensions which psychologists consider to be the fundamental personality traits present in all humans.
The Big Five are extrovertism, conscientiousness, agreeableness, openess and neuroticism and each individual is ranked on all of those scales.
Women with above average neuroticism are characterised as being prone to anxiety, depression and moodiness.
Dr Lummaa said the apparent link between lower BMI and neuroticism was another area needing further exploration, both in Western and developing societies.
She said: ”It is generally though there is a link between the amount of resources a family has and the number of children.
”If you have a really big family it is hard to look after them as well.
”But it could also have its origins in early nutrition. If a mother is stressed out she could end up having smaller babies.
”There are no studies into this but how personality traits affect the success of childbirth is something people should look into more.
”Gaining understanding of such determinants helps in the current debate on the role of individual versus social factors in explaining recent fertility changes around the world.”
The study also looked at men within the village communities, some of who had multiple wives.
Individuals with above average levels of extroversion, meaning they were more sociable and outgoing, had 14 per cent more children than their less extrovert brothers.
The paper was published on Monday in the Proceedings of the National Academy of Sciences.
