This paper reports an interview case study with two physics doctoral students designed to explore their conceptions about the theory of evolution. Analysis of interview transcripts reveals that both students mistakenly constructed a "theory of evolution by environmentally driven adaptation" instead of the commonly accepted "theory of evolution by natural selection and random genetic changes" based on similar Lamarckian misconceptions shared by many contemporary high school and college students. Further analysis shows that their single-process "physicist" synthesis of evolution consists of the following four internally consistent misconceptions: (1) Evolution of traits over time occurs as a result of environmentally induced and directed adaptation by organisms, (2) The quality of traits changes gradually over generations in evolution, (3) Acquired traits can be inherited, and (4) Variation within populations is of little significance in evolution. Preliminary analysis suggests that a major cause of these two physics graduates' misconceptions about evolution might be their misinterpreting the scientific term "adapt" in terms of the meaning used in the everyday context. Implications for improving school biology education are discussed in light of major findings of the study.