A compelling body of scholarship exists which proposes that religious and spiritual beliefs exist in every human society because they reflect fundamental aspects of evolved human nature. This raises the question: why do atheists exist and are atheism and non-belief unnatural? A diverse and growing literature on irreligion reveals that distinct personality and cognitive styles are associated with atheists and non-believers. They are slightly less social than religious believers, less conformist, and more individualistic. Atheists in particular are over-represented among scientists and academics, and their high intellectual achievement may stem in part from their preference for logic and their enjoyment of rational reasoning. Lacking interest in a reality beyond this world, non-believers focus their moral concerns on social justice and the here-and-now. This suggests that non-believers possess cognitive and personality strengths, in contrast to the negative assessments that have been historically the norm. This characterization provides a foundation for asking new research questions, such as whether these traits were adaptive during evolution, or whether they are artifacts of the current historical period, given that characteristics such as skepticism and nonconformity may facilitate rejecting the dominant cultural tradition.