Natural selection associated with birth weight. II. Stabilizing and directional components

Area of Science:

• Perinatal mortality
• Birth weight distributions
• Evolutionary biology

Background:

• Perinatal mortality significantly influences infant survival and development.
• Understanding selection pressures on birth weight is crucial for perinatal health research.

Purpose of the Study:

• To analyze how perinatal mortality components affect birth weight distributions in Italian singletons born in 1974.
• To differentiate selection patterns (stabilizing vs. directional) in mature versus immature infants.

Main Methods:

• Retrospective analysis of birth weight data for all singletons born in Italy in 1974.
• Comparison of birth weight distributions before and after selection events related to perinatal mortality components.

Main Results:

• In mature infants, selection was predominantly stabilizing, with minimal directional influence on birth weight.
• In immature infants, both stabilizing and directional selection were observed, significantly altering birth weight distributions.

Conclusions:

• Perinatal mortality exerts differential selection pressures on birth weight based on infant maturity.
• Selection on birth weight is complex, involving both stabilizing and directional components, particularly in immature neonates.