Learning science interpreted in existing theoretical frameworks often means that students are assimilated, accommodated or enculturated from the entity of the vernacular world to the entity of the scientific world. However, there are some unsolved questions as to how students can best learn purely a new language or new knowledge of science. The purpose of this study is to conduct microanalysis of moment-to-moment interactions in order to understand how science language is taught and learned in details. Informed by Bakhtin's dialogism, the analysis indicates that learning science is a process of appropriating authoritative discourse into internally persuasive discourse. Based on our analysis and findings, we propose the framework of discursive evolution to describe the process of teaching and learning the language of science. Four different stages of discursive evolution are identified to demonstrate the discursive changes during the course of science teaching and learning discourse: (a) using deictic references to connect scientific terminologies, (b) understanding science terminologies through its derivatives, (c) communicating science practices conventionally through science terminologies, and (d) communicating science practices innovatively through mutated science terminologies. The findings suggest that science teaching and learning comprise a heterogeneous process which draws on both science and non-science language and is a constantly evolving process. Understanding teaching and learning as a heterogeneous and constantly evolving process allows us to reunite the roles of teachers and students as mutually responsible collaborators rather than science knowledge givers and consumers.