Conclusion

Aristotelian philosophy held that the o (ãdos, distinguishing essence) of something resided in that quality which made it different from everything else. When we need to know with certainty who an individual is, or whether he is who he claims to be, we normally rely either upon something that he uniquely possesses (such as a key or a card), something that he uniquely knows (such as a password or PIN), or a unique biological characteristic (such as his appearance). Technologically the first two of these criteria have been the easiest to confirm automatically, but they are also the least reliable, since (in Aristotelian terms) they do not necessarily make this individual different from all others. Today we hold that the uniqueness of a person arises from the trio of his genetic genotype, its expression as phenotype, and the sum of his experiences. For purposes of rapid and reliable personal identification, the first and third of these cannot readily be exploited: DNA testing is neither real-time nor unintrusive; and experiences are only as secure as testimony. The remaining unique identifiers are phenotypic characteristics. It is hard to imagine one better suited than a protected, immutable, internal organ of the eye, that is readily visible externally and that reveals random morphogenesis of high statistical complexity.

Acknowledgments: Supported in part by U.S. National Science Foundation Presidential Young Investigator Award No. IRI-8858819 and by research grants from Kodak Corporation.