twenty eleven only shows the author name if more than one author is writing in the blog.
done by this line in style.css:
.single-author .entry-meta .by-author {
display: none;
}
however, the author name is shown in the single post's meta data.
also, in content-single.php, this conditional code is controlling the output of the author bio info in single posts:
<?php if ( get_the_author_meta( 'description' ) && is_multi_author() ) : // If a user has filled out their description and this is a multi-author blog, show a bio on their entries ?>