Evolutionary success relies on life history traits that influence our capacity to grow, reproduce and survive. One critical trait is the generation interval, defined as the average time between two consecutive generations. Small-sized and short-lived species, such as rodents, reproduce and die early, facilitating rapid recovery from previous population declines, as well as quick adaptation to sudden environmental changes. This life history strategy often, but not always, correlates with larger population sizes, and thus entails lower extinction risks in comparison with long-lived megafauna. However, as any other phenotype, generation intervals can vary within each species owing to behavioural plasticity or evolutionary adaptations. In periods or regions of abundance, individuals may mate earlier, indirectly promoting genetic variants that facilitate this behaviour. Conversely, habitat fragmentation and resource scarcity may compromise newborn survival if parents are inexperienced, effectively delaying their reproduction age.

Reconstructing generation intervals over time is paramount for characterizing the past and predicting the future of biodiversity in the face of current environmental crises. Studying life history traits has traditionally involved time-consuming experiments on model species that do not represent the entire tree of life1. In humans, only one study has attempted to estimate generation intervals from genomic data to date2. However, this method relied solely on the evolution of the mutation spectrum over time, which — inconveniently — is affected by confounding factors in addition to age at conception3.