In recent years, clear signs indicate that the human population explosion is coming to an end. Worldwide fertility decline has become so persistent, steep and widespread that it now confronts our species with a new peril, more sinister than that of Malthus: the upcoming collapse of our global population. Many demographers have alerted us to this trend, but their warnings have been widely ignored. Perhaps this is because none have spelled out the dire and inescapable ramifications of the phenomenon. Straightforward reasoning from the best-established principles of evolutionary biology demonstrates that fertility decline is not an ephemeral phenomenon, but will proceed to its ultimate endpoint, no matter what we try to do about it. The Price of Reason presents the argument with a brevity and clarity that will please the academic reader or advanced student, while remaining accessible to the concerned layman. The Price of Reason also expands this new understanding of our human condition into its broader context, placing the fact of our imminent extinction into a wider historical and philosophical context. The Western intellectual tradition is re-examined, from Socrates to Kant to Darwin to Schrödinger, and onward to the unfolding discourse within today's sciences and humanities.