In addition to studying identical twins (who result from the splitting of one egg fertilized by one sperm and who share all of their genes) and fraternal twins (who come from two eggs fertilized by different sperm and who share on average half their genes, just as non-twin siblings do), Segal is the only researcher known to study "virtual" or "pseudo" twins. These are two people less than nine months apart in age but with different biological parents, who are raised together from infancy. Her studies in progress show a modest degree of similarity in virtual twins for general intelligence and special mental abilities.