There is a lot more in humans’ lives than having children. There are numerous differences between humans and other animals. While it may be true that the purpose of animals’ lives is to produce offspring, it is not the case when we talk about humans. People, being much more complex creatures, can contribute to society in many other ways than by having kids (for instance by artistic or scientific activities). So, although our physiology and behaviour may point to reproduction as the main purpose of our lives, these indicators are simply misleading.