Centuries-old database reveals clues on human reproductive habits, trends

June 08, 2016

COLUMBIA, Mo. - When predicting future global population growth, sometimes scientists look to the past. Using a database with historical records that began in 871 A.D., an anthropologist at the University of Missouri was able to show reproductive patterns and shed new light on the "quantity-quality" trade-off, a biological concept used to describe a parent's unconscious decisions to balance between the time and financial investment needed to produce offspring. Results from this study could help to predict future population growth and could help explain how parents allocate their time and financial resources in raising their children.

"The database is probably the best record of human reproduction on earth, with centuries' worth of data," said Robert Lynch, a post-doctoral fellow in anthropology in the MU College of Arts and Science. "Using this incredible resource, we evaluated the relationships and trade-offs among fertility, mortality and parental investment, or the amount of time parents spend in child-rearing. We also wanted to see how parental investment -- including the amount of time and financial resources parents spend with each of their children -- impacted the lifespans and reproductive success of offspring."

Lynch, in partnership with deCode Genetics, analyzed data from individuals born between 1700 and 1919. These dates were chosen to ensure the data were reliable and that all individuals in the study had complete life histories. The analyses examined the relationship between mortality rates and lifetime reproduction.

The study found that parents and offspring do not have similar lifespans or reproductive patterns. However, siblings who share the same mother and father (referred to as "full siblings") were found to have similar lifespans and reproductive success. These similarities among full siblings suggests that parental investment impacts how successful their children are when they decide to reproduce. The study also found that parents who had more full siblings had shorter lifespans and reproduced less. In other words each subsequent full sibling imposed a fitness cost on all the previous ones.

"It is important for parents to maintain a balance between investment, which can be hard to measure, and reproduction," Lynch said. "It also is important to recognize that, as a result of the investment balance that is struck by the parents, there is a cost to children when they have more siblings. For each additional sibling, the cost is one year of life less for their brothers or sisters and siblings may have fewer children. So, when people ask me how long they will live or how many kids they will have, I tell them to look to their siblings."

With the results from this study, Lynch is expanding familial relationships to include half siblings and first cousins to further establish the impact of parental investment on reproductive success of offspring. Half siblings and first cousins share genetic traits; yet they lack many key environmental factors, like a shared household, Lynch said.

The study, "Parents Face Quantity-Quality Trade-Offs Between Reproduction and Investment in Offspring in Iceland," recently was published by the Royal Society Open Science.
Editor's Note: For more on the story, please see: https://coas.missouri.edu/news/parental-dilemma-more-kids-or-better-outcomes

University of Missouri-Columbia

Related Siblings Articles from Brightsurf:

Stars and planets grow up together as siblings
ALMA shows rings around the still-growing proto-star IRS 63

Study of siblings finds moderate cannabis use impacts cognitive functioning
A new study led by researchers from the University of Colorado School of Medicine compares adolescent siblings to determine the impact of early and frequent use of marijuana on cognitive function.

Child disability can reduce educational outcomes for older siblings
A recent paper published in The Economic Journal indicates that, in families with disabled children, the second born child is more adversely affected cognitively than the first-born child.

Siblings of children with intellectual disabilities score high on empathy and closeness
A new Tel Aviv University and University of Haifa study finds that relationships between children and their siblings with intellectual disabilities are more positive than those between typically developing siblings.

Genome testing for siblings of kids with autism may detect ASD before symptoms appear
One of the key priorities of interventions for autism spectrum disorder (ASD) is starting early, with some evidence showing infants as young as seven months old could benefit.

New study debunks myth that only children are more narcissistic than kids with siblings
The stereotype that only children are selfish, or more self-centered than those with siblings is sometimes used as an argument for having more than one child, but researchers from Germany find there's no evidence for the claim that only children are more narcissistic than children with sibling.

Children bullied by friends and siblings are more likely to think about suicide in their early 20s
Depression, self-harm and suicidal ideation are more prominent in adults in their early twenties if they were bullied at home and at school, a study by researchers at the University of Warwick have found.

UBC study finds siblings of problem gamblers also impulsive, prone to risk-taking
Biological siblings of people with gambling disorder also display markers of increased impulsivity and risk-taking, according to a new UBC psychology study.

Québec siblings with rare orphan disease lead to discovery of rare genetic diseases
Mutations in a gene involved in brain development have led to the discovery of two new neurodevelopmental diseases by an international team led by researchers at McGill University and CHU Sainte-Justine Research Center.

The more the merrier? Children with multiple siblings more susceptible to bullying
A child with more than one brother or sister is more likely to be the victim of sibling bullying than those with only one sibling, and firstborn children and older brothers tend to be the perpetrators, according to research published by the American Psychological Association.

Read More: Siblings News and Siblings Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.