will show the same markers as a person in question can range from 1 in 2 (such as in type O) to 1 in several thousand (such as when many systems are typed and a relatively rare type is found). The literature and case law on paternity disputes suggest that a likelihood of 1 in 20 is reasonably corroborative and that a likelihood of only 1 in 100 can strongly influence the triers of fact.
Thus, although conventional serology can exclude a person, it can also include many members of a population group as the possible origin of a blood, saliva, or seminal fluid stain. Conventional serology is further limited, in that analysis of mixed-fluid stains in which two or more contributors are involved can mask an individual donor. Similarly, only 75-80% of the population are secretors (exhibit their ABO blood type in their other physiological fluids). Thus, the combination of those factors severely limits the power of conventional forensic serological examinations as an individual identifier. Results of serological analysis also are more subjective and can give rise to differing conclusions when interpreted by equally qualified scientists.
Hair evidence is often encountered in sexual assault and other violent crimes. It is valuable as exculpatory evidence and can be informative as to identity, but it lacks specificity. Although hair examiners can associate a hair with racial characteristics and body source (trunk, head, or pubic area) the variations among hairs on a given person make definitive association of a single hair with an individual problematic. The microscopic comparison of hairs is also subjective and can lead to differences of opinion among equally qualified experts. With the advent of DNA technology, especially PCR amplification techniques, the use of hair as an individual identifier will become more common.
Some other forms of individual identification are available to forensic scientists, but have very limited application. For example, examination of teeth is useful in identifying deceased persons or bite marks.
Providing scientific evidence that DNA technology is at least as reliable as other forensic methods and is therefore more likely to result in definitive identification or exclusion of persons suspected or accused of a crime satisfies both the ethical concerns about individual rights and the conditions of an ethical analysis based on weighing good and bad consequences. However, additional assurances are required for the risk-benefit ratio to be favorable in each case in which the technology is used. Therefore, a critical step in accepting the use of DNA technology in criminal trials is establishing safeguards and seeking to prevent abuses.
Even if a technology is scientifically sound and its use is ethically permissible, it is necessary to seek to prevent abuses and misuses in prac-