Economic tradition establishes that human beings' reproductive behaviour is based on rational actions. This theory is completely plausible; however, there is another part to this story, whatever else we may be, we are animals, and this biological heritage instinctively affects our reproductive strategy. Human beings want to extend their genes through time. We test this hypothesis using panel data models for 52 countries from 1995 to 2009, controlling for cultural, social and economic variables, and find a positive and statistically significant effect of the threat of violent death on the fertility rate. Countries characterised by a high murder rate have a high fertility rate. Apparently, there is an instinctive pattern to be found in our reproductive strategy; we are not as rational as we suppose.