The manosphere is a collection of online antifeminist men’s groups whose ideologies often invoke Darwinian principles and evolutionary psychological research. In the present study, we reveal that the manosphere generates its own untested and speculative evolutionary hypotheses, or “just-so stories”, about men, women, and society. This is a unique phenomenon, where lay (i.e., non-expert) individuals creatively employ evolutionary reasoning to explain phenomena in accordance with their particular worldview. We thus assembled the first dataset of lay evolutionary just-so stories extracted from manosphere content (n = 102). Through qualitative analysis, we highlight the particularity of the manosphere’s lay evolutionism. It is a collective bottom-up endeavor, which often leads to practical advice and exhibits a male gender bias. We further show that 83.3% of manosphere just-so stories pertain to sex differences, and that only 36.3% explicitly signal that they are speculative. Given this evidence that lay communities collectively engage in evolutionary hypothesizing, we reflect on implications for evolutionary scholars and for the field as a whole, in terms of ethics and public image. Lastly, we issue a call for renewed discussion and reflection on evolutionary hypothesizing, a central yet somewhat neglected feature of evolutionary behavioral science.