more complicated to maintain, especially since many exotic living organisms were not visible in natura or in vivo but had to be evoked by specimens or specific writings. Collections thus assumed the role of an external memory for humanity, allowing a relationship with nature, in the same way as books, gardens or menageries do, the latter having the disadvantage of being materially more complicated to maintain.
It is thus possible to trace an evolution in the nature of collections from the collections of the schools of natural history, from that of Aristotle to those of the Renaissance, then to cabinets of curiosities, and finally those of the first great museums, places of European power in a world expanding toward new places of commercial activities (spices, silk, precious woods, coffee, etc.).
During this period, from Mediterranean Antiquity to the European Renaissance, collections and writings came into resonance. These collections had to be ordered according to a system or catalogued. Vernacular taxonomies were no longer sufficient to name organisms that were no longer encountered on a daily basis in the natural environment and whose numbers were beyond individual human memory. Natural histories such as Aristotle’s testify to this process, which began a long time ago. However, it was not until the post-Renaissance period that the real beginning of a taxonomic literature based on binominal nomenclature (Linnaeus 1758) was noted. This literature took over from individual expertise and gradually gave shape to a collaborative system to which naturalists from different countries could contribute. This system still exists today because of natural history museums and the scientific literature in taxonomy.
The aim of natural history literature was to form a catalogue of Life, the mineral or the human. For practical reasons, this rapidly growing catalogue could not only be enumerative, it had to be classificatory. A classification allows us to find our way through an immense set of objects, with logical rules that propose a guiding structure in a too-long list by constituting groups of species that are subordinate to each other. The classifications have thus very quickly made it possible to navigate efficiently in a rapidly-growing sector of knowledge.
But what classification could have been constructed if not one that made sense, a meaning so obvious that everyone wished to use it for communication within society? This meaning, on which the first classifications were based, is the orderliness of Life that the great naturalists of the 18th century perceived and then interpreted as resulting from biological evolution (Perrier 1886; Le Guyader 2003).
Through this interaction between collections and classifications, the museums and their collections have thus helped the emergence of the idea of biological evolution that is central to biology today. Similar aspects have taken place for other types of collections, such as minerals or human artifacts. In the case of minerals, for example, classification is based on their chemical composition and thus developed with modern chemistry in the 19th century.
2.3. The structuring of our thoughts and actions by an ancient concept
The traditional vision of collections thus recapitulates these successive societal motivations at the historical level: the satisfaction of curiosity, the cataloguing of diversity with the formulation of the notion of species (essentialist, then biological for living organisms or chemical for minerals) and finally, recently, the organization of knowledge with the notion of evolution for living organisms. Curiosity for the natural world has, nevertheless, remained great, to the point of being the driving force behind the pedagogy offered by museums in their exhibitions.
The beginning of a more structured interest in biological diversity and the scientific refinement of the notion of species fueled very applied approaches, even if they proved to be extraordinarily powerful and innovative in many scientific respects. The naturalists of European museums actually supported the economic efforts of the great kingdoms with their ability to classify and to name important exotic resources. Subsequently, population biologists designed genetic tools for the improvement of domesticated, cultivated or bred species (Fischer 1930). The notion of species coupled with genetics thus became an important societal tool and all kinds of conservatoires and genetic data banks were created in that context. All this can also be said regarding the study of the diversity of mineral resources, which brought the Industrial Revolution by offering societies other materials and sources of energy than wood or earth, such as bronze, iron and their modern industrial companion, coal.
In the context of all these advances, the role of collections remained frozen at the stage of description of the diversity of Life, presumptively resulting from evolution. Therefore, collections are still a reference for the description and the identification of species. In this respect, 2.4 million species are known to science, while about 10 million probably exist in ecosystems today (estimates vary according to different authors but are rarely below this order of magnitude) May 2004; Costello et al. 2012)). Collections are growing steadily with taxonomic work (Tancoigne and Dubois 2013) and the continuation of field sampling, to the point that their overall size is difficult to estimate (Arino 2010).
However, for many decision-makers or non-natural history scientists, the reference role of collections is often perceived as limited, to the point that science policy articles regularly appear questioning the slow pace or even the quality of the taxonomic process of exploring living species and classifying them (Charles and Godfray 2002; Grandcolas 2017b, pp. 116–128). Many authors erroneously believed that living species are already well-known and we should just add coherence to the current system and rush to provide the necessary additions (May 2004; Padial et al. 2010; Costello et al. 2013). In reality, this view only takes into account the basic taxonomic description: we only know about 20% of living species, and still very imperfectly. It should be remembered that out of these 2.4 million described species, only a few tens of thousands are known for more than a taxonomic description and some elements of geographical distribution. In addition, many of them are already extinct or have become exceedingly rare in natural environments (Regnier et al. 2015). Moreover, even at the purely classificatory level, the taxonomic system is scientific and collaborative, and incessant corrections are made to the supposedly already acquired knowledge that is, in reality, very imperfect (Vaidya et al. 2018).
It is also important to understand that these living organisms that are still unknown to science do not only include rare “exotic” species or sisters of known species without much immediate societal interest: so-called exotic, unknown or unrecognized species remind us incessantly when we are confronted with a new “plague” or vector or pathogen for humans. For example, the recent discovery in France of exotic flatworms that have been introduced, are invasive and are predators of earthworms, leads to understanding of how much these organisms are totally misunderstood and scorned by everyone, including most scientists (Justine et al. 2018). Everyone then understands momentarily how valuable collections are and how they allow us to situate a species in relation to existing knowledge about living species in relation to taxon names.
We are therefore rather stuck in this traditional vision of collections as a matter of curiosity, repertoire and support for the study of evolution, in the narrow context of indispensable but very focused studies of taxonomy and evolution. We need to reintegrate natural history collections into more diverse scientific and societal issues by starting again from the fundamentals.
2.4. Collections: more than species catalogues
In terms of fundamentals, it is important to realize that collections are samples of living organisms that reflect not only specific richness but also genetic and phenotypic diversity among individuals. This goes against the traditional taxonomic conception that considers collections like Noah’s ark, where the list of different species is proof of their importance. In fact, the sum of natural history collections in different institutions allows us to examine many individuals assigned to different species and not to study biological diversity with a simplistic view which would consider each species as invariant. Moreover, it must be understood that the notion of species is an operational facility to designate networks of relationships between individuals whose limits are somewhat imprecise. The species is not a natural kind or individual, and each identification and assignation to a species is an arbitrary scientific decision: a species cannot be enumerated on