The issue of the secular state is pertinent in Latin America, especially in countries like Brazil, where religion may influence the political and educational field. Data from a survey of biology teachers regarding the teaching of evolution in Argentina, Brazil and Uruguay were analysed, recognising the secularity of the countries. The BIOHEAD-CITIZEN questionnaire and semi-structured interviews were used in this research. Two questions were highlighted: one regarding teachers' opinion on the separation of politics and religion and the other on the separation of science and religion. In both, the results from Brazilian biology teachers stand out, with a greater alignment with the conception that religion can participate in the political and academic sphere. The interviews also confirmed that Brazilian teachers must deal with religious clashes, with students and in their personal conceptions, when teaching evolutionary theory. This situation is of concern in the current Brazilian political context (Bolsonaro government), in which the theme of religion is in evidence in politics, and may become increasingly so in the school environment, notably in relation to the teaching of biological evolution.