Replies to Google Groups defalt to being *from* the group

When I reply to an email sent to any Google Group to which I belong, my reply defaults to being from the group’s email address, not from my personal email address. I can manually switch this each time but I don’t always remember and this has been problematic when responding to the original sender only, and having my reply go out to the entire group.

Why is this the case, and how do I fix it so that all email I send defaults to being from me?