I'd say there might be an 'optimum' somewhere in between - on average slightly lower rate than replacement, aiming for sustainable decline without crisis, preserving cultural heritage - as human cultural diversity matters as well as biodiversity. But we lack intelligent discussion of this topic - partly as it’s hard for people to imagine intuitively how small annual changes integrate over time.I'd like to further develop my interactive model - designed for climate projections but including a demographic model, to help people experiment for themselves, including regarding potential changes in global migration fluxes.