The demographic transition is a process where societies change from having lots of babies and high death rates to having fewer babies and lower death rates. This shift happens as societies become more modern. In the past, people had fewer children than they could have because of customs like marrying late or breastfeeding for a long time. Nowadays, people use contraception to have fewer kids on purpose. A study in Europe found that factors like education and urban living don't always predict how many children people have. Instead, cultural traditions and religion play a big role. But as societies become more modern, they tend to have fewer children and lower death rates.