Response to LTG on Wildlife Forensics:

The following is an explanation of why taxonomic classifications in wildlife forensics do not

require statistical support in the same way that declarations of a “match” in human DNA or in

pattern disciplines such toolmark analysis do.

In wildlife forensics, an examiner identifies a sample as belonging to a particular taxonomic

level (e.g. species) by looking up the set of characteristics that define that taxonomic level and

determining whether the sample has those characteristics. New species are continually being

identified, based on additional characteristics that scientists find, including both morphological

features (e.g. a pink snout) and sequencing (e.g. a particular mtDNA haplotype). This process

involves validation in the sense that scientists ensure through research that new taxonomic level

definitions are based on characteristics that are new, distinguishable, and identifiable in a

repeatable, reliable manner.

But the discipline does not require population variability studies to determine whether a sample

belongs to a particular taxonomic level. That is because taxonomic definitions are based on

invariant characters that are diagnostic for the taxon. Particular species may exhibit great

variability, but variable characters are not included in the species definition. Thus, unlike

disciplines seeking to attribute a particular sample to a particular source based on the rarity of

shared features, in wildlife forensics, any sample exhibiting the diagnostic characteristics

associated with a taxonomic level belongs to that level BY DEFINITION. For example, a sample

that an examiner identifies as having all the diagnostic characteristics of the species Alligator

mississippiensis, is, by definition, a member of that species, because taxonomists have defined

that species to include all animals that have those characteristics.

Thus, the only source of error in an examiner’s determination that a sample belongs to a

taxonomic level (e.g. species) is the examiner’s identification of the characteristics the sample

has. Once the examiner correctly identifies the characteristics, and the characteristics that define

the taxonomic level (e.g. the characteristics that define the genus Alligator, or the species

Alligator mississippiensis), any sample with those defining characteristics is a member of that

level by definition. If a sample is only partial or damaged or degraded, an examiner might only

be able to classify the sample as belonging to a higher taxonomic level (e.g. as a member of the

genus Alligator, but not any particular species of Alligator). Note that species identification only

identifies a sample as having the defining characteristics of a particular taxonomic level. It does

not involve the individual identification of a member within the taxonomic group.

Of course, like in other disciplines, examiners might commit errors in determining the

characteristics a sample has (either morphological or sequencing). An estimate of such an error

rate could be determined, like in other disciplines, through performance studies. As in other

disciplines, this error rate would vary depending on the examiner’s experience, training, skill

level, and judgment, and whether the examiner’s determination is subject to verification. We do

not read this standard as speaking to performance studies; the standard merely explains why
statistical statements are not appropriate for species identification made based on the

documentation of definitional characters.