Vol.:(0123456789) 1 3 Primates https://doi.org/10.1007/s10329-018-0667-6 REVIEW ARTICLE The role of indirect evidence and traditional ecological knowledge in the discovery and description of new ape and monkey species since 1980 Lorenzo Rossi 1  · Spartaco Gippoliti 2  · Francesco Maria Angelici 3 Received: 25 October 2017 / Accepted: 28 May 2018 © Japan Monkey Centre and Springer Japan KK, part of Springer Nature 2018 Abstract Although empirical data are necessary to describe new species, their discoveries can be guided from the survey of the so- called circumstantial evidence (that indirectly determines the existence or nonexistence of a fact). Yet this type of evidence, generally linked to traditional ecological knowledge (TEK), is often disputed by ield biologists due to its uncertain nature and, on account of that, generally untapped by them. To verify this behavior and the utility of circumstantial evidence, we reviewed the existing literature about the species of apes and monkeys described or rediscovered since January 1, 1980 and submitted a poll to the authors. The results show that circumstantial evidence has proved to be useful in 40.5% of the exam- ined cases and point to the possibility that its use could speed up the process at the heart of the discovery and description of new species, an essential step for conservation purposes. Keywords New species · Traditional ecological knowledge · Ethnozoology · Conservation Introduction In legal jargon, indirect (or circumstantial) evidence is the evidence submitted by a party involved in a trial, which allows somebody to reach conclusions that indirectly deter- mine the existence or nonexistence of an event that the party tries to prove (Wigmore 1935). Indirect evidence is distin- guished from direct evidence, which is, on the contrary, able to prove the existence of an event without the need for any inferences and assumptions (Wigmore 1935). Considering the diferent nature of these two kinds of evidence and their use in the ield of zoology, it is possi- ble to notice an interesting correlation between indirect and direct evidence, and the processes behind the discovery and description of a new species. First, it must be stressed that ‘discovery’ and ‘description’ are diferent concepts and that they are not always close in time (Pine 1994). Further- more, even the nature of the evidence needed to discover and describe a species is not always the same. If the formal description of a species requires direct evidence, that is a holotype, its discovery prior to the formal description could still be guided exclusively by circumstantial evidence (see results). Indirect evidence of the existence of a new species, or the survival of species declared extinct, often becomes so-called traditional ecological knowledge (TEK) because locals gen- erally know well the animals who share a territory with them (e.g., Carpaneto and Germi 1989; Voss and Fleck 2011). From this point of view, it is worth bearing in mind that the concept of ‘discovery of a species’ does not have an absolute signiicance: the need to classify and order nature is a behav- ior typical in all cultures (e.g., Berlin 1992). So, if there is traditional knowledge, a folk description or a local name of a species, it becomes part of an ‘ethnotaxonomy’ system that can be considered already ‘discovered’ by locals. It follows that often a ‘new species’ is new only from the point of view of western science (e.g., Heuvelmans 1982). Despite the high rate of loss of habitats and biodiversity (e.g., Dirzo and Raven 2003; Barnosky et al. 2011), new mammal species continue to be discovered and described (e.g., Reeder et al. 2007), while many others are still waiting * Lorenzo Rossi info@associazioneorango.com 1 Associazione Orango, via San Cristoforo 196, Cesena 47522, Italy 2 Società Italiana per la Storia della Fauna “Giuseppe Altobello”, Viale Liegi 48, Rome 00198, Italy 3 FIZV, via Marco Aurelio 2, Rome 00152, Italy