Reproduction is seasonal across all living organisms, from plants, and insects, to reptiles, birds, mammals, and even humans. The first documentation of seasonality in human births goes back to European studies in the early 19th century. Studies throughout the 20th century noted that seasonality of births varied from location to location, but they focused on either one location for a long time, or many locations over a short time span. Jürgen Aschoff, labeled as the father of chronobiology, remarked that the lack of experimental possibilities to investigate birth seasonality must be compensated by a comparative analysis of data that are widely distributed in time and area. I aim to do just that, by collecting the largest dataset of births to date, and uncovering spatiotemporal patterns in birth rates, the timing of the birth pulse, and the strength of that birth pulse. Together, these three covariates (birth rate, timing of the birth pulse, and strength of the birth pulse) comprise my definition of 'Birth Seasonality' used throughout my website. Click one of the boxes below to explore more about birth seasonality in developed countries in the Northern Hemisphere, or in currently developing countries.
Monthly human birth rates in the United States from 1931-2008, as shown by state. Vertical striping indicates strong seasonal patterns in births. From Martinez-Bakker, Bakker, Rohani, and King, 2014.