title: Reduced birth intervals following the birth of children with long-term illness: evidence supporting a conditional evolved response.
abstract: Human birth interval length is indicative of the level of parental investment that a child will receive: a short interval following birth means that parental resources must be split with a younger sibling during a period when the older sibling remains highly dependent on their parents. From a life-history theoretical perspective, it is likely that there are evolved mechanisms that serve to maximize fitness depending on context. One context that would be expected to result in short birth intervals, and lowered parental investment, is after a child with low expected fitness is born. Here, data drawn from a longitudinal British birth cohort study were used to test whether birth intervals were shorter following the birth of a child with a long-term health problem. Data on the timing of 4543 births were analysed using discrete-time event history analysis. The results were consistent with the hypothesis: birth intervals were shorter following the birth of a child diagnosed by a medical professional with a severe but non-fatal medical condition. Covariates in the analysis were also significantly associated with birth interval length: births of twins or multiple births, and relationship break-up were associated with significantly longer birth intervals.
authors.affiliation: School of Medicine, Bond University, Gold Coast, Queensland 4229, Australia dwaynfor@bond.edu.au.
authors.forename: David
authors.initials: D
authors.lastname: Waynforth
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D001721:Birth Intervals / Q000706:statistics & numerical data*; D002648:Child; D002675:Child, Preschool; D002908:Chronic Disease; D015331:Cohort Studies; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D017533:Marital Status; D008875:Middle Aged; D009099:Multiple Birth Offspring; D010290:Parents / Q000523:psychology; D012044:Regression Analysis; D012189:Retrospective Studies; D035781:Siblings; D006113:United Kingdom / Q000453:epidemiology; D055815:Young Adult
keywords: interbirth interval; life-history theory; parental investment; trade-offs