More Obj-C like version of an SO answer - http://stackoverflow.com/a/4251473/743957

gistfile1.m

#import <objc/runtime.h>

- (BOOL) class:(Class)classA descendsFromClass:(Class)classB
{
	while (1)
	{
		if (classA == classB) return true;
		id superClass = class_getSuperclass(classA);
		if (classA == superClass) return (superClass == classB);
		classA = superClass;
	}
}