In a scenario I sketched in a previous post to a related question (see link below), laughter is a coping mechanism for certain untoward situations and therefore presupposes perception thereof, which in turn presupposes consciousness. Anything to do with humor would be a later development and social in nature.
Examining this problem requires we first look at humor itself. Why do we laugh and why do we find certain things funny?
Why do month old babies laugh? What are they laughing at?
Humor appears to be a mild social correction mechanism. If someone slips on a banana peel and does not really get hurt we laugh. It embarrasses the person who fell and he will be more careful next time.
If he slips on the banana peel and breaks his back we do not laugh. Laughter has no corrective force here.
Babies laugh to stimulate attention from there mothers. There is probably not much in the way of external stimuli that causes it until they are older.
Many people can laugh at jokes but few have a true "sense-of-humor." True comedians who can twist common situations and make them appear funny.
Comedians are mild social critics who don't take themselves or others too seriously but try to use humor to correct or criticize.