Human beings have been facing apocalyptic circumstances for thousands of years. Our competitors, our nemesis have been pathogens like malaria, Yersinia Pestis, smallpox... every few generations, a cataclysmic plague would tear through human populations and leave entire towns uninhabited. In the modern era, with modern medicines, we may feel that - at least in the industrialized West - this horror is behind our species now. But with evolving technology and behaviours come new risks; and we have seen in pandemics like Zika and Ebola that there may well be terrors yet to come for humanity. What makes these pandemics so threatening? And what has natural selection and evolution produced in the way of pandemics? NOTE: This is part 1 of a two part series on pandemics; the second part will deal with biotechnology-inspired viruses and pandemics. If you're enjoying the end of the world, why not hit us up with episode suggestions on twitter @physicspod? You can donate to the show via Paypal there - every little helps us cover our costs. Please rate and review the show on iTunes if you don't want to donate - it helps us get noticed by generous, physics-loving billionaires. Until next time, stay safe.