Our data indicate that 100 species of vertebrates are related to some type of taboo. Although the patterns of the taboo/species relationship are not clear, it is possible to identify that some animals are rejected as food due to characteristics of the meat, and it is pointed out that consuming some species can aggravate inflammatory processes. At this point, it is necessary to consider that taboos consist of unwritten or defined social rules, generally symbolizing something forbidden and untouchable, without necessarily having a rational explanation [20].

Observing the ecological aspect, the taboos behave like restrictions or rejections that govern attitudes and actions regarding a natural resource, constructed based on the human perception of a certain species. Consequently, species can be avoided because of their behavioral patterns, morphological characteristics, toxicity or simply because they are involved in myths and represent religious symbols, which are part of the cosmology of a population [8, 21]. Examples of species such as Nycticebus javanicus, Funambulus pennantii, Pardofelis marmorata and Catopuma temminckii are related in Asia to ancestral relationships, totemic symbols and religious beliefs that protect these species against hunting [28, 29, 46].

It is important to understand how humans seek, obtain and choose food, as food choices can be influenced by individual preferences, ecological, economic, social and cultural factors, as well as dislikes [22]. In this situation, food taboos often limit the use of natural resources and, therefore, have important implications for biodiversity conservation [19, 23, 24].

It is noticeable that taboos are heterogeneously distributed among animal classes, this perspective is possibly related to selective pressures, which led human beings to interact differently with fish, birds and reptiles. About fish, the literature points out many species with an inflammatory potential for humans. It is possible that human populations have developed fish-related taboos to reduce the risks associated with potentially inflammatory foods [4, 25]. Another point is that the rejection for consumption of certain species of fish happens due to the animal's eating conditions, as well as its morphology. For example, species such as poraquê (Electrophorus electricus) and the sarapo (Sternarchorhynchus mormyrus) are avoided by Brazilian communities because they are like snakes, so in the local perception, they may contain some toxicity [1].

About mammals, the ancestry between humans and other animals of this taxon may be a factor that influences behaviors that originate taboos. As humans recognize characters in common with other mammals, this may lead to dietary restrictions for animals with anthropomorphic characteristics. Traditional peoples of China tend to avoid the Gibbon (Hoolock tianxing) as food, due to the belief that the species is “ancestors of people” [26]; it is also found that indigenous peoples of India do not hunt or consume any primates, due to the belief that primates were their ancestors and, therefore, are religious symbols [27]. In this way, shared ancestry, religious symbols and the belief that the species causes or intensifies inflammation can make a species taboo [4, 14, 25,26,27,28,29,30,31,32].

The taboos associated with reptiles and birds report situations of restriction to the meat of these animals due to sacred contexts or potential inflammation. Regarding reptiles, the emergence of taboos associated with these animals may be related to the feeling of fear. Most likely, humans' fear of reptiles is related to genes that arose in ancient lineages of mammals that were preyed on by snakes. Thus, the human feeling of fear is associated with these genes, possibly favoring the survival capacity of Homo sapiens against animals with some risk potential, such as snakes [50,51,52].

About the taboos related to birds, the human feeling about birds is directly associated with the beauty of these animals. Birds are seen by humans as beautiful animals due to their coloration [53]. Colors such as blue and yellow are seen, especially in birds, as elements that enhance beauty [54]. Possibly, this feeling influences a low number of birds used for food and, consequently, fewer food taboos. Additionally, the taboos assigned to birds that have been listed here are related to restrictions constructed by local sacred aspects. It is also necessary to consider that this taxon is directly linked to smuggling, in which several birds are sold in Brazil and in the world, causing birds to be incorporated into pet and trade categories [55, 56].

Taboos can be classified in a utilitarian way, such as temporary (segmental) taboos that are restricted to certain periods of life, regulating the use of a resource according to age, gender, social condition and other specific conditions; and permanent (specific) that extend throughout life [19]. As for the variation in the types of taboos, the segmental taboos predominated in relation to the other types of taboos observed in the studies. Many of these segmental taboos are associated with the inflammatory potential of meat. These animals are known as “reimosos” in South America. The word “reima” comes from the Greek “rheum” which means “viscous fluid” and aims to classify the degree of safety of wild and domestic animals for consumption [1].

Creamy or “heavy” foods, for traditional populations, tend to provoke or aggravate inflammatory processes, tending to be avoided by people in physical states of liminality, initiated in some ritual, people with illnesses, menstrual period and postpartum [12, 33]. In our study, we found 50 cases of taboos referring to “heavy animals,” many of which were described as “heavy meat” animals capable of causing infections, being foods to be avoided mainly by women during pregnancy, puerperium or menstruation. This perspective is recurrent in riverside communities in the Amazon (Basil), where some reptiles such as the Jabutis (Peltocephalus dumerilianus), (Mesoclemmys raniceps) and the jabuti-tinga (Chelonoidis denticulatus) are not eaten because they are oily, because they are “offensive to anyone eats,” causing “allergic reactions” [14]. Several other cases of segmental taboos are cited in this review [1, 4, 11, 14, 31, 34,35,36,37,38]. These examples of segmental taboos point out how cultural factors and the phases of a person's natural life cycle can interfere in the dynamics of animal consumption in a community, and this instrument ends up being an important factor for the conservation of animal species.

Specific taboos are mostly related to religious factors and folk beliefs. In a case study, it is seen that the capture and consumption of primacy Nycticebus javanicus is prohibited because, according to villagers, taking and keeping this species in homes can bring unhappiness and bad luck [28]. On the other hand, in India, felines such as Capped Langur (Trachypithecus pileatus), Asian golden cat (Catopuma temminckii), cat-marbled (Pardofelis marmorata) and the tiger (Panthera tigris) are seen as animals that bring luck, because they are related to sacred institutions and cannot be hunted [27].

Habitat taboos are also considered a type of permanent taboo. This type of taboo was characterized by restrictions on hunting in places considered sacred. These places, because they are surrounded by symbology and spirituality, serve as a sanctuary for animals, thus being an important conservation factor. According to local beliefs, people who hunt in sacred places can suffer both divine and popular punishments [39]. Janaki et al. [27] point out that habitat taboos can help in the conservation of wild animals by providing refuges. Habitat taboos are recurrent in continents such as South America, Asia and Oceania, and these sacred reserves help government institutions to institutionalize places as biodiversity conservation areas, making them heritage protected by law.

The studies found are mostly from South America, reinforcing the perspective that this continent is one of the main scientific productions related to Ethnobiology [40]. It can be noticed that regarding taboo game species in South America, the vast majority of studies are focused on the fish group, with case studies being carried out with indigenous and riverside peoples, mainly in the Brazilian Amazon, in addition to caiçaras (mixture ethnocultural heritage of indigenous, European and African peoples) from the coastal portion of Brazil [1, 2, 4, 11, 25, 30, 38]. On the other hand, no studies were found that portrayed taboos associated with fish in Asia, Oceania and Africa. And only one study was found in Europe [41].

The greatest restriction for fish consumption in South America was due to the potential to cause inflammation, the feeding habits of these animals, in addition to the morphological similarities with snakes for some species [4, 25, 32]. In Asia, Africa, Oceania and Europe, it is noticeable that the taboos are similar, since most food restrictions are based on spirituality, where species, mainly mammals and reptiles, are prohibited so that the hunter/consumer does not suffer “punishments,” divine powers or punishments in their village/tribe [27, 28, 39, 42, 43].

By observing the behavior of taboos within the socioecological systems present in this review, it was found that food taboos have a positive effect on fauna conservation. This is because, even if unintentionally, the people involved end up acting in favor of the conservation of the species, either by restricting the consumption of “loaded” meat that can cause illness or by situations associated with the sacred place that can result in punishments for those who consume [14, 27, 43].

The literature directly discusses the effect of taboo on fauna conservation [13, 21]. The compilation of data on taboos across the planet corroborates this perspective, as the data collected here show that food taboos have a positive effect on animal conservation, as of the 100 species listed under the effects of food taboos, 99 have taboos with positive effects for these species. These results show how taboos play a fundamental role in conservation and are often neglected by representations of formal institutions.

Analyzing the conservation status of the species listed here, we observe that the species classified as critically endangered (CR) in the IUCN list, as is the case of the hawksbill turtle (Eretmochelys imbricata) and the small primate the slow loris (Nycticebus javanicus) have taboos that reduce access by humans. We can presume that these species, without local taboos, could be susceptible to a decrease in population density in several regions of their occurrence [28, 31, 44].

However, it is important to consider the limitations of the effect of food taboos within a conservationist perspective [21, 57]. Some species may present local taboos and have their consumption avoided, but form part of the diet of other human populations. For example, the present study shows that Tayassu pecari, Pecari tajacu and Nasua nasua have a record of food taboos in Brazil; however, it is used in food in different parts of northeastern Brazil [58, 59]. Additionally, species such as Mazama americana, Mazama gouazoubira, Dasypus novemcinctus and Cuniculus paca have food taboos in Argentina but are preferred items in food in some locations in Brazil [55, 59].

Considering that habitat loss (because of urbanization and agribusiness) [60, 61] directly impacts wildlife, the existence of food taboos, even at the local level, plays an important role in conservation. If we consider that the food taboo has a local effect, the absence of these social rules could trigger greater pressure on certain species of animals, as their consumption would be widely spread. In this way, a species of animal avoided by a certain social group tends to have a higher population density at the local level, thus contributing to conservation. For example, in a study on sacred groves, it is demonstrated that the taboo of habitat serves to regulate the use of natural resources, being recognized by traditional communities as more efficient than areas of environmental protection [57]. Segmental taboos have also been identified as important wildlife managers, since they reduce the number of people who consume the resource [30].

The data collected here show that there are still few studies on food taboos and their consequences for preserving fauna. Thus, any strong conclusion about the role of taboos in conservation is still premature. However, it is possible to use these data and incorporate them into strategies to support fauna conservation. Taboos associated with the sacred are efficient mechanisms in the conservation of fauna. In a case study in Ghana (Africa), it is pointed out that among a community of turtles such as E. imbricata, Dermochelys coriacea, Lepidochelys olivaceae and Chelonia mydas are not hunted, due to local belief that these turtles were sighted saving ancestors of the population during a war against the Ashanti empire (an important ethnic group in Ghana). Therefore, residents of this village are prevented from consuming meat from these reptiles [44]. In the Brazilian Amazon, the taboo exerts a positive force (conservation) on species such as Tapirus terrestres, Tayassu fishermen, Fishermen steal and Ateles chamek which are avoided by indigenous peoples of the lower Madeira River, as they are considered to aggravate inflammation [7].

The consensus among studies is that animals considered taboo tend to be preserved, and this can positively impact the population dynamics of these species. It is estimated that the existence of taboos can reduce the pressure exerted on some species by up to 80%, since taboos reduce the number of people sharing the resource [4, 13, 14]. At this point, it was identified that only one work points to a negative relationship of taboos associated with wild species; it was found that in Oceania, flying fox hunting (Tongan priest) is intensified, due to the belief that the population of this species is infinite within a sacred area, so hunting the species in other areas does not impact the population of the animal [43].

Considering the types of taboos, it is observed that the specific and habitat taboos, as they are permanent, contribute to the formulation of laws and other regulations to prevent the hunting of different species of animals [57], showing the importance of the taboo even for formal institutions as technical and legal mechanisms for the conservation of species, corroborating the study by Nijman and Nekaris [28], which points out that species-specific taboos may have important ecological ramifications for the protection of threatened populations.