Evolutionarily speaking, it makes sense to have a lot of children. At the very least, we might expect a population to replace itself, with each couple having an average of two children. However, this evolutionary logic is not mirrored by current data: birth rates are falling in the UK, with many people choosing to either have one child, or no children at all. We speak to evolutionary anthropologist Dr Paula Sheppard about the drivers, and consequences, of this observed trend.