That different races have effectively the same intellectual capacities is surely an important part of why we treat them as moral equals. But this doesn't seem to me to be entirely necessary — young children and the mentally handicapped may deserve most (though not all) moral rights, while having a substantially lower level of intelligence. Intelligence might also turn out not to be sufficient; if a lot of why we care about other humans is that they can experience suffering and pleasure, and if intelligent behavior is possible without affective and evaluative states like those, then we might be able to build an AI that rivaled our intelligence but did not qualify as a moral patient, or did not qualify as one to the same extent as less-intelligent-but-more-suffering-prone entities.