Transcript: When we think about life in the universe, we tend not to think of microbial life clinging to a planet around a nearby star. We tend to think in terms of intelligent life. But in terms of talking about the probability of intelligence elsewhere in the universe, we have to understand the role of intelligence in the evolution of life on Earth. Large brains with the capability for intelligence probably evolved as a natural consequence of natural selection. Brains would have conveyed an adaptive advantage on complex creatures that had brains, because these nerve centers for the organism would have enabled superior hunting strategies and strategies with dealing with the climate with its variations, and predators. However, it’s not obvious that large brains with the capability for abstract thought are an inevitable consequence of evolution. For example, we share the planet with blue-green algae, and simple microbial organisms that have lived for billions of years, and in essence are far more successful life forms than humans are. Also, if humans or other intelligent species disappeared from the planet, which is the fate of almost all species, there is no guarantee, and it’s not obvious, that intelligence would once again arise.