How can he say, "everything can be explained by science?" His life stands in obvious refutation of this claim. Science surely can't explain why he felt uncomfortable as a girl and wanted to switch genders. It's likely that those against his freedom to choose his gender identification would cite science as foundation of their disapproval. There is much in human existence beyond the reach of science. I guess he didn't get to read any of the  classics in high school. 

Science can't explain much of the "how" nor can it even competently address the bigger existential question of "why."