grep -rlZ --exclude-dir=dir1 --exclude-dir=dir2 HUMAN . |
 xargs -r0 rm -f

If you want `find` to do the directory traversal:

 find . -type d \( -name dir1 -o -name dir2 \) -prune -o \
 -type f -exec grep -lZ HUMAN {} + |
 xargs -r0 rm -f

Portably/standardly, that would have to be:

 find . -type d \( -name dir1 -o -name dir2 \) -prune -o \
 -type f -exec grep -q HUMAN {} \; -exec rm -f {} +

but that means running one `grep` per file.