Are domesticated animals dumber than their wild relatives? A comprehensive review on the domestication effects on animal cognitive performance

Animal domestication leads to diverse behavioral, physiological, and neurocognitive changes in domesticated species compared to their wild relatives. However, the widely held belief that domesticated species are inherently less "intelligent" (i


Introduction
Animal domestication is a crucial turning point in human history, playing an important role in the development of human society (Vigne, 2011;Zeder, 2015).What began as an unintentional process evolved into a deliberate endeavor, leading to the emergence of selection pressures that progressively molded animals to thrive in human-created environments and adapt to human lifestyles (Larson and Fuller, 2014;Price, 2002).By relying on domesticated animals, our ancestors were able to create large, sedentary communities that relied on agriculture for sustenance.Beyond the reliance on a more stable food source, the domestication of animals allowed for new forms of labor and transportation, which in turn facilitated the progress of commerce and trade within and between cities. Domestication of animals has also had a long-lasting impact on the natural world, leading to permanent changes in some ecosystems, with the alteration of diverse landscapes to meet human and animals' needs (Terrell et al., 2003;Vigne, 2011).In essence, the domestication of animals represents one of the defining characteristics of the Anthropocene, the current geological age marked by human impact on the planet (Chansigaud, 2020).
It is worth noting that animal domestication is far from a straightforward, single-path journey.Instead, it unfolds as a prolonged and intricate co-evolutionary process, characterized by various stages along distinct pathways (Larson and Fuller, 2014).Three separate pathways stand out in the wild animals' journey towards domestication: the directed pathway, the commensal pathway, and the prey pathway (Zeder, 2012).The directed pathway involves deliberate and purposeful human efforts to domesticate a species.In this scenario, wild animals were brought into the human environment and subjected to a series of pressures, prompting them to adapt in a way that would lead to domestication.While this is perhaps the most well-known pathway (all the recent domesticateshamsters, gerbils, freshwater and marine species -are the result of a directed pathway), the initial evolutionary process of animal domestication primarily occurred through the commensal and prey pathways.The commensal pathway (or self-domestication scenario, Marshall-Pescini et al., 2017a) suggests that for certain species, such wolves, some individuals took the initiative to exploit the human environment as a source of food.In this first stage, individuals were already facing selective pressures, with less fearful ones having an advantage in exploring this new niche compared to more fearful individuals.Subsequently, in a second stage, humans began a more direct selection, favoring animals with specific traits like reduced aggression and increased cooperation (Larson and Fuller, 2014;Marshall-Pescini et al., 2017a).Finally, the prey pathway proposes that domestication occurred unintentionally for some hunted species, such as sheep, goats, pigs, and cows, as part of efforts to enhance resource management.To prevent overhunting and resource depletion, humans started employing management strategies, leading to an intensive association with these species, eventually culminating in their domestication (Larson and Fuller, 2014;Zeder, 2012).
Animal domestication has occurred in various parts of the world, but not all human societies have engaged in this transformative process.For domestication to occur, several conditions must be met.First, access to a domesticable species is required.These species are typically social animals that form a stable hierarchical system and have feeding habits that do not compete with humans (Zeder, 2012).Secondly, environmental pressures such as predation and starvation must be reduced or even eliminated to provide an environment suitable for domestic animals to thrive.Thirdly, preferred traits must be favored and their selection must be intensified and guided by human principles.This process involves selecting animals with desirable traits, such as reduced fearfulness and high fertility, and using those traits to breed future generations.Finally, even in captivity, animals must undergo natural selection under artificial conditions, leading to better adaptation of individuals to their surroundings (Boice, 1981;Jensen, 2006).The combination of these four different processes sets domestication apart from simply taming a wild animal or placing it in captivity.Unlike the latter actions, which are temporary and isolated, the effects of domestication on genetics and phenotype are substantial and lasting, remaining for generations (Chansigaud, 2020).
The similarities in behavior between domestic and wild animals, such as pigs and wild boars that build nest before farrowing, domestic chickens and red junglefowl that perch, or the urge of wild and laboratory rats to explore (if given the possibility) (Eklund and Jensen, 2011;Jensen, 1986;Pisula et al., 2012a), highlight certain ancestral needs that persist in domestic animals despite years of artificial selection.However, the differences between domestic and wild animals are numerous and varied: the process of domestication has resulted in a shared set of traits among domestic species, collectively known as the "domesticated phenotype" or "domestication syndrome" (Wilkins et al., 2014; but see Lord et al., 2020, andWright et al., 2020 for a critical opinion on the animal domestication syndrome).Domestic animals often display distinct morphological features, such as larger body size and a faster growth rate, but shorter skulls and reduced relative brain size, compared to their wild counterparts (Balcarcel et al., 2022;Brusini et al., 2018;Katajamaa et al., 2021;Katajamaa and Jensen, 2020;Kruska, 1988).Physiologically, domestic animals possess increased reproductive capacity, and display earlier sexual maturation (Künzl et al., 2003;Setchell, 1992).In terms of behavior, domestic animals exhibit reduced fear and anti-predator behaviors (Lachambre et al., 2017;Reimers and Svela, 2001;Suzuki et al., 2013;Tobias Krause and Schrader, 2016;Yamanashi et al., 2016).These characteristic differences may demonstrate the profound impact that intense selection can have on shaping the evolution of species.
Although beneficial from a productive (or even aesthetical) point of view, some of these changes, such as the reduced brain size and altered behavioral patterns, reinforced the idea to the general public, but also among researchers, that domestic animals are less smart than their wild relatives.This perception has, at times, cast animal domestication in a negative light, portraying it as a form of degeneration and leading to the notion that domestic animals cannot, in any form, represent their wild conspecifics (Boice, 1981;Brusini et al., 2018;Brust and Guenther, 2015;Kruska, 1988).
From an evolutionary perspective, it can be hypothesized that domestic animals, due to their evolution in simpler and more predictable environments, may have experienced a reduction in selection pressures leading to a potential decrease in their cognitive abilities and performance compared to their wild counterparts (Albiach-Serrano et al., 2012;Brust and Guenther, 2015;Price, 1999).However, this view may not necessarily be factual.While humans have been able to thrive and develop their societies with the help of domestic animals, this interdependence has not been one-sided; animals, too, have undergone evolutionary changes, enhancing various traits to more effectively adapt to human environments (Gustafsson et al., 1999).The domestic dog is an excellent example of this: the dog's abilities in reading human cues are considered by many to be a cognitive advancement (Hare et al., 2010;Salomons et al., 2021, but see Lea andOsthaus, 2018, andRange andMarshall-Pescini, 2022 for critical reviews that reject this perspective).However, as we will explore later, it is essential to acknowledge that domestication might not solely be the catalyst behind enhanced sociocognitive skills toward humans: even wild animals have demonstrated the ability to follow human cues and exhibit similar interspecific social behaviors (Danel et al., 2023;Essler et al., 2017;Ketchaisri et al., 2019).
Despite the multitude of comparative studies done between dogs and wolves (Marshall-Pescini et al., 2017a;Range and Marshall-Pescini, 2022;Udell et al., 2010a), there has been little research on how domestication has affected other taxa's perception and processing of information from their physical and social environments and is an area that requires further study.
To deepen our understanding of the relationship between animal domestication and cognitive performance, in this comprehensive review, we critically evaluated, through a comparative approach, different papers that investigated the cognitive abilities/performance of domesticated species and their wild relatives.Our primary objective is to address a frequently asked question (Kruska, 1988): do domesticated animals have poorer (or simply different) cognitive abilities than their wild relatives?As we delve into the subsequent sections, it becomes evident that the literature comparing cognition between domestic and wild individuals has yet to yield a definitive answer to this question.It is essential to acknowledge the limitations of the current data before interpreting its findings.Contemporary literature reviews have begun to address this question to some extent, drawing upon the abundant comparative research between dogs and wolves (Lea and Osthaus, 2018;Range and Marshall-Pescini, 2022;Udell et al., 2010a).To avoid redundancy, our secondary objective is to present a discerning overview of the existing literature, encompassing not only dogs but also other relevant species.By evaluating the available evidence, we hope to offer a comprehensive overview of the field, including its limitations and potential for future research.

Methods
Following Jardat and Lansade (2021), our literature search was carried out in the Web of Science database (https://www.webofscience.com) from September 2022 to February 2023.The search was based on two concepts: a) 'Animal domestication' and related terms, and b) 'cognitive abilities' and related terms (Table 1).As researchers on animal domestication may disagree on what species can be considered as domesticated or not (Chansigaud, 2020), we included the main researched domesticated species and their wild relatives (such as dogs/wolves, wild boar/domestic pig, red junglefowl/chicken), but also keep our search as open as possible, using terms such as 'animal domestication' and 'domesticated animal'.
The first part of the search query was enclosed in parentheses and consisted of two nested sub-queries: The first sub-query was enclosed searched for the terms "domestic" and "wild", along with a list of common researched domesticated animal species.The second sub-query, as well the query for cognitive abilities, uses the OR operator to search for additional animal species (and their known wild relatives), meaning that at least one keyword must be present in the text of the publications selected.The concepts were combined with 'and', so that only publications containing both concepts were selected.Only articles in English were considered.Twenty Web of Science Category filters were applied to select relevant scientific domains and type of articles (Veterinary Sciences, Zoology, Agriculture Dairy Animal Science, Ecology, Behavioral sciences, Multidisciplinary Sciences, Agronomy, Evolutionary Biology, Biology, Fisheries, Marine Freshwater Biology, Psychology Biological, Neurosciences, Psychology Multidisciplinary, Entomology, Psychology Experimental, Ornithology, Psychology, Developmental Biology, Psychology Developmental).
The search yielded 6775 publications whose titles and abstracts were screened for relevance.Studies were included if they compared any type of cognitive ability (with a clear outcomebetter than, worse than, similar to -considering individual performance) between a domestic species and its wild relative.Studies considering cognitive ability/performance of only one species (either domestic or wild) were excluded.We retained 70 publications with these criteria.Complementary research in the References section of the selected articles yielded 4 more publications.

Results
Our literature review results are presented in Table 2, where each species pair -comprising both the wild relative and its domesticated species -is analyzed in terms of their cognitive abilities.The table includes some details on the studies that have explored these abilities, such as the specific cognitive realm (see below), the cognitive trait, and the type of task or test employed for the assessment.Furthermore, the table provides a summary of results, indicating whether the wild individuals performed better, worse, or similar than their domesticated counterparts.
In our analysis of 74 publications, we identified 88 cognitive comparisons between wild and domesticated animals.Among these, domesticated animals outperformed their wild relatives in 26 cases, while wild animals exhibited better performance than their domesticated counterparts in an equal number of cases (26 cases).In 36 instances, wild and domesticated individuals performed similarly.More than half of the publications (42 out 74) on the topic of our review comes from studies on wolves and dogs, followed by 11 publications on wild and domesticated rat strains and 7 publications on red junglefowl and domestic chickens.The other nine species pairs were investigated in one to three publications each (wild boar and domestic pig, wild and domestic mice, wild cavy and domestic Guinea pig, wild and domestic laboratory gerbils, wild and domestic ferrets, wild and domestic zebra finch strains, white-backed munia and the domestic Bengalese finch, wild and domesticated mallards, wild-caught and domesticated sea bass).
We have taken an additional step by categorizing these various studies into three distinct realms of cognition: physical cognition, social cognition (intraspecific or interspecific), and general cognition (Krichbaum et al., 2020).Physical cognition involves the cognitive processes that enable animals to comprehend the objects in their surroundings, as well as their spatial and causal relationships.This domain encompasses essential aspects such as spatial orientation, categorization, numerical ability, object permanence, reasoning, tool use, and foraging-related problem solving, among other significant factors (Nawroth et al., 2019).Social cognition, on the other hand, refers to all cognitive processes relating to interactions with conspecifics or heterospecifics.It includes communication, cooperation, learning from others, and understanding others' emotions, attentional states, and intentions (Krichbaum et al., 2020;Nawroth et al., 2019).Finally, we also explore general cognition, which comprises cognitive processes that do not fit into the physical or social cognitive domains.These are fundamental processes that underlie most behaviors and enable animals to adapt to a variety of contexts.General cognition includes aspects such as attention, memory, and learning.Additionally, it encompasses executive functions, such as working memory and inhibitory control, which involve effortful, goal-directed behavior, enabling animals to adapt and exhibit optimal behavioral patterns (Krichbaum et al., 2020).
When we examine the studies considering the three aforementioned cognitive realms, a noticeable pattern emerges.The majority of conducted studies have primarily focused on investigating the connection between domestication and general cognition, accounting for 36 out of 88 studies.This is followed by 34 studies that delve into social cognition, and a smaller number of 18 studies that specifically address physical cognition.While studies on physical and general cognition exhibit a more balanced distribution across different species, it is noteworthy that research on social cognition is largely concentrated on dogs and wolves, with 29 out of 34 studies centering around these species.The remaining five studies investigate social cognition in wild boar and domestic pigs, wild and domestic ferrets, red junglefowl and domestic chickens, and white-backed munia and the domesticated strain Bengalese Finch.
A detailed examination of Table 2 reveals that, among the species investigated in these two cognitive realms, Norway rats and domestic dogs (along with their wild counterparts) have the most extensive comparative data available.Notably, in the case of rats, no study reported that wild rats exhibited superior cognitive performance compared to domestic rats.In contrast, domestic rats either performed better (8 out of 13 studies) or showed similar cognitive abilities (5 out of 13 studies) when compared to their wild counterparts.A striking contrast emerges when analyzing the comparison between dogs and wolves.Out of the 22 studies that have investigated these two species, more than half of them (12 studies) demonstrate that wolves outperform dogs in the general/physical cognitive realms.Additionally, six studies found no significant difference in performance between dogs and wolves, while only four studies indicated better cognitive abilities in dogs compared to wolves.
Similar to dogs, domestic chickens also appeared to exhibit comparatively lower performance in the general/physical cognitive realms.Four studies suggested that the chickens' wild relative, the red junglefowl, outperformed their domestic counterparts in terms of learning spatial information and displaying greater flexibility.However, two recent studies have brought these findings into question, indicating that domestic chickens might possess similar spatial orientation and habituation reactions to red junglefowl (Bessa Ferreira et al., 2022;Ferreira et al., 2022).
The remaining studied species exhibited less apparent result patterns, primarily because there is a limited number of studies and data available for them.Consequently, drawing consistent trends for these species becomes infeasible.
As evident from the beginning of this review and from Table 2, the majority of studies investigating cognitive differences between domestic and wild animals have predominantly centered around a single pair of species: dogs and wolves.The abundance of studies comparing dogs and wolves comes as no surprise, given the privileged position that dogs hold in the field of comparative cognition research.Dogs possess a unique combination of traits within phylogenetic, ecological, and anthropogenic contexts, as they are carnivorous, social hunters, and domestic animals simultaneously (Lea and Osthaus, 2018).Their accessibility as individuals, often as pets that can be readily brought to the laboratory, or even as street dogs, eliminates the need for complex husbandry or extensive veterinary expenses, further bolstering their suitability as research subjects.Moreover, the opportunity to compare them with their wild relative, the wolf, under similar experimental conditions, makes the dog/wolf model particularly intriguing for investigating fundamental questions related to domestication and cognition (McCreary et al., 2023).
While the dog/wolf studies have indeed provided valuable insights into how domestication influences cognition, our current understanding of the broader relationship between domestication and cognitive abilities remains limited.As a result, we are unable to find a conclusive answer to the question posed in this paper.The diverse and sometimes contradictory findings from the different studies raise more questions than they answer.For instance, it is essential to explore whether the effects of domestication on cognition are specific to certain species (reflecting the unique cognitive demands developed over the course of their domestication) or if they arise due to limitations in the design or execution of each study (as discussed in the following sections).To gain a more accurate understanding of how domestication relates to cognition, it is crucial to expand research efforts beyond the traditionally studied species.Exploring the relationship between domestication and cognition in other species and investigating various cognitive realms, different cognitive traits, and utilizing diverse testing methods may enable us to validate and gain a more comprehensive understanding of past and future findings.

Does domestication improve socio-cognitive abilities towards conspecifics and humans?
Based on our literature review, we find ourselves farther from answering this question than the previous one.While numerous studies have explored physical and general cognition across various species, there remains a significant lack of comparative data between domesticated and wild species, particularly in the realm of social cognition, with the primary focus on dogs.
At the intraspecific level, among the nine studies on dogs, none suggest that dogs outperform wolves in intraspecific social cognition.Instead, the evidence indicates that wolves excel in multiple aspects, including cooperation, social learning, and prosociality (4 out of 9 studies), while in other cases, wolves exhibit similar abilities to dogs (5 out of 9 studies).Rather than attributing these findings to dogs' cognitive limitations, Marshall-Pescini et al. (2017a) propose a comprehensive view that extends beyond domestication alone when comparing dogs and wolves.They emphasize that changes in dog social ecology, such as alterations in their feeding habits and niche from group-hunting to scavenging, along with shifts in their social organization from pair bonding to promiscuity, have played a crucial role in shaping the behavioral and cognitive profiles of dogs.The authors advocate for the integration of these factors as significant contributors to the observed differences in social cognition between domesticated dogs and their wild relatives (Marshall-Pescini et al., 2017a;Range and Marshall-Pescini, 2022).
To date, there are only three studies, involving a species pair other than dog/wolf, that has investigated intraspecific social cognition differences between domesticated and wild species.One study involved a social learning task conducted on domestic chickens and red junglefowl.In this task, a demonstrator bird showed another observer individual how to access a food reward.Surprisingly, domestic chickens demonstrated greater ease in learning from each other compared to red junglefowl.The authors suggested that domestic chickens, having been selected to live in larger and more dynamic groups than red junglefowl, may have developed enhanced social learning abilities as a result (Rutkauskaite and Jensen, 2022).The other two studies focused on song learning and song complexity in both the white-backed munia and its domesticated strain, the Bengalese finch.The findings from these studies were intriguing.It was observed that domesticated finches exhibited lower accuracy when copying a tutor's song compared to wild munias, who seemed more bound to the song they were exposed to.In addition to this, researchers also delved into the intricacies of their song complexity: the songs of munias were found to be more stereotyped and simpler, while the finches' songs displayed greater variability and complexity.The authors of these studies put forward an interesting hypothesis to explain these observations.They suggested that since domesticated birds face reduced predation pressure, they are less constrained to develop a precise song.Instead, they have the opportunity to invest more in increasing the complexity of their songs, a trait that is often favored by female birds during courtship and mate selection (Honda and Okanoya, 1999;Takahasi and Okanoya, 2010).
At the interspecific level, the majority of studies (21 out of 23) was on the sociocognitive skills of dogs in relation to humans.Most of these focused on human/dog-wolf communication, while two other studies investigated the use of human cues on wild boar vs. domestic pigs and wild vs. domesticated ferrets (Albiach-Serrano et al., 2012;Hernádi et al., 2012).
In contrast to the patterns observed in the previous sections on physical and general realms, as well as intraspecific social cognition, the results at the interspecific social cognition level exhibit a different trend.Out of the 23 studies conducted, domesticated individuals outperformed their wild counterparts in nine instances, while in thirteen other studies, both wild and domesticated individuals performed similarly.Interestingly, in only one case (wolves vs. dogs), the wild relatives appeared to demonstrate better cognitive performance.
The "Evolutionary Social Competence Hypothesis" posits that the interplay of natural and artificial selection has led to heightened interspecific social competence in domesticated animals, particularly in dogs (Miklósi and Topál, 2013).This increased social competence is suggested to have emerged as a result of humans becoming an integral part of these animals' environment during the process of domestication (Miklósi and Topál, 2013;Range and Marshall-Pescini, 2022).However, it is worth noting that while this hypothesis may partly align with the current literature results, a recent review by Range and Marshall-Pescini (2022) has shed light on the limitations of studies that claim interspecific cognitive superiority of dogs when compared to wolves.They argue that many of the tasks used to assess dogs' superior social cognition towards humans are controversial and may not be measuring what they intend to.For example, although dogs may outperform wolves in human pointing tasks in three different studies (Hare et al., 2002;Salomons et al., 2021;Virányi et al., 2008), it is possible that dogs perceive the human pointing as a command rather than a cooperative sign.This interpretation finds support in two studies, revealing that dogs, having been primarily selected for their trainability, tend to perform better in training tasks, that involve forced learning, in contrast to wolves (Frank, 2011;Frank and Frank, 1983).Similarly, when dogs are observed looking back at human experimenters during an impossible task (Miklósi et al., 2003), it may be due to their low persistency during tasks and the fact that they may be responding to the most salient stimulus in their environment, i.e., the human nearby, rather than exhibiting greater communicative ability than wolves (Marshall-Pescini et al., 2017b;Range and Marshall-Pescini, 2022).
Further studies comparing dogs and wolves revealed that, although domestication did modify different aspects of social behavior of domesticated animals (i.e., their social-ecology, Marshall-Pescini et al., 2017a; Range and Marshall-Pescini, 2022), it may not be a pre-requisite for human-like social cognition in canids.Ontogenetic experiences also seem to play an important role in canine performance during human-related cognitive tasks: wolves that were given proper socialization with humans were seen to outperform dogs in following human cues (Udell et al., 2008) and to have a similar performance to dogs in perspective taking tasks (Udell et al., 2011).
To bolster the argument that ontogenetic experiences significantly impact cognitive performance, a comparison between pet dogs, research dogs, and shelter dogs sheds light on these dynamics.Pet dogs, with ample human contact and socialization, were observed to outperform research dogs and shelter dogs on following human cues, the latter groups having limited exposure to human contact.In fact, research and shelter dogs showed difficulty in following certain types of human pointing cues (Lazarowski and Dorman, 2015;Udell et al., 2010b).It becomes evident that acknowledging the differences between sub-populations within the same domestic species is crucial, as they exhibit varying cognitive abilities and responses (Range and Marshall-Pescini, 2022).A comprehensive understanding of these disparities requires consideration of the interplay between genetic, developmental, and experiential factors, all of which contribute to shaping the cognitive profiles of domestic animals (Udell et al., 2010b).Domestication alone cannot account for all sociocognitive skills observed in animals.Studies focusing on non-domesticated captive species have provided intriguing insights, demonstrating that even wild animals are capable of communication with humans.For instance, research on human-habituated kangaroos revealed that they exhibit gazing and gaze alternations towards humans when confronted with an unsolvable task (McElligott et al., 2020).Similarly, megachiropteran bats were observed to use human pointing to locate hidden food (Hall et al., 2011).Notably, in the bat study, it was found that wild-born individuals habituated to humans were unable to follow human pointing, in contrast to their captive-born counterparts.This finding suggests that early human socialization from an early age plays a crucial role in predicting individual performance (Hall et al., 2011).
Combined, these findings underscore that animal-human communication is remarkably widespread, exceeding initial expectations.Moreover, the cognitive abilities enabling such communication can be learned during an individual's development, contingent upon animals' acceptance of humans as social companions and their conditioning to follow human cues, particularly in response to human limbs (McElligott et al., 2020; see Udell et al., 2010a for more information on the "Two-stage hypothesis").
To better understand how domestication has changed the way species perceive and interact with humans, more studies are necessary, including a more diverse range of wild and domesticated species, as well as non-domesticated species, to determine which factors contribute to the development of these abilities (McElligott et al., 2020).

Limitations and research opportunities
When evaluating research comparing the cognitive abilities of wild and domesticated species, it is crucial to consider confounding factors that may affect the results.In the following sections, we will discuss these factors in greater detail and highlight the research questions that still require further investigation.

Environmental influences and cognitive performance
To allow for a better and valid comparison between the cognitive abilities of domesticated species and their wild relatives, researchers often rely on standardized laboratory settings where both groups of animals can be studied under controlled conditions.In this approach, wild animals are usually captured, kept and bred in captive environments, allowing for a more standardized comparison between them and their domesticated counterparts.By controlling variables such as diet, social environment, and exposure to human interaction, researchers can minimize the impact of extraneous factors and better understand the relative cognitive abilities of ancestral species compared to their modern domesticated congeners.
Despite efforts to control for certain factors, such as the physical and social environment, it is crucial to acknowledge that several confounding variables may still influence the cognitive performance of the animals.Therefore, it is important to exercise caution when interpreting the results of comparisons between domesticated and wild species.
One of the key confounding factors when comparing the cognition of domesticated and wild animals is the fact that extragenetic, experiential variables may be an important source of phenotypic variation between individuals (Lickliter and Ness, 1990).Domesticated animals typically reside in controlled and stable environments, which tend to offer limited exposure to various environmental challenges (however, it is worth noting that their increased interaction with humans can potentially stimulate their cognitive processes specifically in relation to humans, as discussed in the previous session).On the contrary, wild animals, particularly of the founding generation (F0), are exposed to a much wider range of unpredictable and complex ecological and evolutionary pressures, including dietary challenges, predator-prey interactions, and other unique experiences from their natural habitat.These experiences can significantly shape the cognitive abilities of both domesticated animals and their wild relatives, beyond the impact of domestication alone.
There is growing evidence to suggest that the behavior of domesticated animals is not as different from their wild counterparts as we once thought (Price, 1999).Some researchers suggest the existent differences are mainly due to the fact that domesticated animals are exposed to an impoverished environment and cannot express their full behavioral panel, as do their wild relatives (Lickliter and Ness, 1990).Numerous studies have shown that simple changes, such as the addition of environmental enrichment to a captive setting, can reveal species-typical behaviors in domesticated animals that are strikingly similar to those of their wild relatives.For example, gerbils that were allowed a shelter in their laboratory cages were more similar, at the behavioral and physiological levels, to their wild counterparts, than gerbils reared in standard cages (Clark and Galef, 1981, 1980, 1979, 1977).Similar results were found for wild/domesticated rats and ducks (Boice, 1977;Miller, 1977).
To control for environmental variation (and influence) in the rearing of studied individuals, wild animals are often housed and bred in captive conditions, making their offspring, a captive-born generation (F1), suitable for comparison with their domesticated counterparts as both groups have had similar physical and social experiences.However, it is crucial to acknowledge that the mere act of housing and breeding wild animals in captivity can initiate a domestication process, which can potentially alter their cognition, even without intentional selective breeding (Håkansson and Jensen, 2008;Lachambre et al., 2017).This has been demonstrated in several studies.For example, in a study of a first generation of hatchery-born abalone (Haliotis tuberculata), individuals showed behavioral and immune responses to different stressors that were better adapted to captive conditions compared to wild-born individuals (Lachambre et al., 2017).Similarly, over only four successive generations in captivity, red junglefowl coming from two populations facing different levels of predatory threat altered their anti-predator behavior and became more similar (Håkansson and Jensen, 2008).
It is therefore worth of note that the absence of meaningful experiences in captivity may increase, but also suppress (due to potential stressful conditions, for example), the differences between domesticated and wild animals, changing the individuals' perception of their environment, and consequently altering their behavior and cognition, independent of domestication status (Bessa Ferreira et al., 2022;Carrete and Tella, 2015;Schetini de Azevedo et al., 2012).
Not all species follow the above-mentioned pattern, though.Some wild animals, such as cavies (Cavia aperea), have been shown to maintain their behavior and physiological characteristics even after 30 generations of captive breeding (Künzl et al., 2003).Similarly, laboratory-reared house mice that had lived in captivity for 10 years did not exhibit any differences from their wild counterparts, although both groups did differ from domesticated laboratory mice (Price, 1984).Understanding why certain species maintain their ancestral traits while others quickly become domesticated without intentional artificial selection is a promising area of research within both comparative cognition and the study of genetic variation within and between species.

Purposes of domestication/selection and cognitive performance
As mentioned earlier, it is crucial to acknowledge that domestication occurred in distinct ways for different species, and the selective pressures acting on each species were also diverse.These variations make it challenging to directly compare cognitive differences between wild and domesticated animals from a single, unified perspective.While data on social cognition are still limited, trends in the physical and general cognitive realms seem to emerge at the species-level.Dogs and chickens appear to exhibit comparatively lower cognitive performance than their wild counterparts, whereas domestic rats show better cognitive abilities than their wild relatives.Interestingly, all three species followed the commensal pathway during their initial domestication process, but subsequent selection varied significantly among them.The domestic rats studied to date come from laboratory populations and were selected to adapt to laboratory conditions (Hulme-Beaman et al., 2021).Chickens, on the other hand, were initially selected for aesthetic, socio-cultural, and/or recreational purposes and later for meat and egg production (Lawal and Hanotte, 2021).In contrast, dogs were initially selected for multiple working tasks, such as hunting, herding, and companionship (Kaminski and Marshall-Pescini, 2014).The variation in selected traits across domesticated animals could be a contributing factor to the diverse patterns of cognitive abilities observed among different species (Miklósi and Soproni, 2006).Domestication may have favored certain species in specific realms while hindering cognitive abilities in others.However, it is important to note that, at present, this explanation remains speculative due to the limited scope of current studies.
At the within-species level, when selecting representatives for a particular domesticated species, careful consideration should be given to the diversity within that species and the potential differences that could exist between subgroups.For example, the laying hen (selected for the increased production of eggs) and broiler chicken (selected for the increased production of meat), both derived from the Red Junglefowl, but exhibit differences in their need and motivation for exploration, with laying hens being more motivated to explore than broiler chickens, despite their shared ancestry (Lindqvist et al., 2006).Additionally, even small variations in selective pressure, such as strains that produce more or less eggs, can result in variations in brain size and composition (Mehlhorn and Caspers, 2021;Mehlhorn and Petow, 2020).The different purposes of selection can therefore be an important source of variation between wild and domesticated individuals of the same species.
The influence of different selection processes on the cognitive abilities of animals is an area of study that remains largely under-explored.While some studies have provided evidence that cognitive performance can vary between different lines/breeds within a species, there is a lack of comprehensive research that compares multiple subgroups of domestic species selected for different purposes to their wild relatives.For instance, a study by Nawroth et al. (2022) compared the cognitive performance of dwarf goats (not selected for any production parameters) and dairy goats (selected for high milk yield) in a visual discrimination learning task and a reversal learning task.The results showed that, while the two groups performed similarly in the first task, the dwarf goats outperformed the dairy goats in the second task.The authors suggest that selection for high milk yield may have altered the behavioral flexibility of dairy goats.In another study, Dudde et al. (2018) compared the learning strategies of white and brown laying hens (300 vs 200 eggs/year, respectively).The results showed that white layers possessed better learning strategies compared to brown layers, indicating that, contrary to the goat study, selection for high productivity may have enabled individuals to acquire energy resources more efficiently.A similar pattern was observed in a study of dogs from working breeds and non-working breeds by Wobber et al. (2009).The results showed that dogs from working breeds, which were bred specifically to respond to human cooperative communicative signals, were more skilled in the comprehension of human communicative signals than dogs from non-working breeds.The same was found on a study on different rat strains: while one strain (Long-Evans) had a better spatial performance than the five other domesticated strains (Dark-Agouti, Fischer 344, Wistar, Sprague-Dawley, and Fischer-Norway), Long-Evans rats did not differ from their wild counterparts, which supports that a differential selection of morphological or non-cognitive behavioral characteristics and/or differential breeding stories may generate differential effects on cognitive performance that are strain-specific (Troy Harker and Whishaw, 2002).
Overall, these findings prompt us to carefully reconsider, with increased caution, the outcomes of certain studies that compare domestic and wild species.For instance, some studies comparing dogs and wolves have been conducted using only pet dogs as representatives of the domestic species (Fiset and Plourde, 2013), while others have specifically focused on certain breeds such as German shepherds (Hiestand, 2011) or Siberian huskies (Range et al., 2012).Similarly, studies comparing domestic chickens and red junglefowl have predominantly used chickens that were selectively bred for egg production (Bessa Ferreira et al., 2022;Ferreira et al., 2022).The current approach of selecting domesticated representatives of a species may not fully capture the wide range of cognitive variations that could exist among different domesticated populations.
In their recent review, Range and Marshall-Pescini (2022) provide V.H.B. Ferreira et al. compelling reasons for carefully considering the representativeness of domesticated subpopulations when comparing them to their wild relatives.The authors suggest that using pet dogs as representatives for studying the domestication process may not yield the most accurate results.This is because dog domestication occurred in two distinct stages, with the more recent stage involving intense artificial selection for specific traits (Larson and Fuller, 2014;Marshall-Pescini et al., 2017a).The strong artificial selection, coupled with the increased experience with humans in pet dogs, has the potential to introduce biases when comparing them to their wild counterparts, such as wolves.
In contrast, free-ranging dogs display a remarkable genetic diversity and are subject not only to selection pressures imposed by humans but also to natural and sexual selection.These various selective pressures were likely active during the early stages of domestication, making the study of free-ranging dogs a more appropriate addition to our understanding of the domestication process (Range and Marshall-Pescini, 2022).
Recent studies comparing various dog populations revealed some disparities in specific cognitive aspects.Notably, free-ranging dogs exhibit distinct behaviors when contrasted with their domesticated pet counterparts.For instance, in the context of how domestic dogs respond to human gaze, free-ranging dogs tend to adapt their gaze behavior according to different human attentional states; they gaze less at the human when the human is inattentive compared to when the human is attentive.In contrast, pet dogs do not display such variations in their gazing behavior under these two conditions (Brubaker et al., 2019).Additionally, when confronted with a novel object containing inaccessible food (an impossible task), free-ranging dogs appear to be less persistent in their attempts compared to pet dogs (Lazzaroni et al., 2019).These distinctions may arise from a combination of diverse life experiences and genetic factors, underscoring the need for further investigation.

Developmental windows and cognitive performance
In their literature review on the social cognition of domestic dogs and wolves, Udell et al. (2010a) point out the importance of making a distinction between the chronological age and the developmental stage when comparing the cognitive performance of domesticated animals and their wild relatives: testing individuals with the same chronological age is not always correct, since domesticated and wild animals have different developmental trajectories.Indeed, the sensitive period for interaction with novel stimuli from physical and social domains is increased in domesticated compared to non-domesticated individuals (Trut et al., 2004), therefore even when tested in the same cognitive task, at the same age, a different behavioral response can be expected.Udell et al. (2010a) raise concerns about the findings of a widely-cited experiment on captive foxes, which reported that, after 45 years of selective breeding for tameness (considered a key trait in animal domestication), fox kits exhibited social-cognitive abilities similar to those of domestic dog pups when it came to following human gestures (Hare et al., 2005).The authors question whether the observed differences between the selected and unselected foxes could be attributed to their respective developmental stages, rather than domestication per se.This is because selection for tameness is known to affect the sensitive period of social development in captive foxes, resulting in a longer sensitive period for the selected foxes compared to the non-selected ones (Trut et al., 2004).To avoid this confounding factor, Udell et al. (2010) recommend that animals should be tested taking into account their developmental stage, which may vary for different species and groups and requires further research.
In the same line of questioning, the series of experiments with adult domestic rats outperforming their wild relatives (as discussed earlier) led the authors to propose an intriguing hypothesis: investigating the learning capabilities of juvenile rats could yield different outcomes.They hypothesize that wild individuals may display heightened learning sensitivity during early life, potentially resulting in increased adaptability compared to their adult counterparts (Boice, 1972).
Given the above considerations, longitudinal studies represent a crucial factor in understanding the development of behavioral and cognitive abilities in both domestic and wild animals over time.However, these studies are currently limited to dogs and wolves.In the subsequent paragraphs, we will explore the evidence pertaining to this particular species pair and demonstrate how considering this evidence can lead to a shift in our interpretation of outcomes.
In their study comparing the behavioral and morphological development of wolf and dog pups, Frank, Frank (1982a) observed that dog pups displayed a prolonged period of fetal/juvenile characteristics when compared to their wolf counterparts, leading the authors to describe dogs as "extraordinarily fetalized" (also known as neoteny (Price, 1984)).Additionally, while six-week-old wolf pups demonstrated well-developed locomotor and motor skills, such as climbing over barriers and walking, six-week-old dog pups were still in the process of learning how to walk.These differences persisted until dogs reached 10-12 weeks of age, at which point they began to catch up to the developmental level of wolf pups.Despite these observable behavioral and morphological differences, in another study, the same authors concluded that six-week-old wolf pups outperformed dog pups in problem-solving/inhibitory control, specifically in a detour task (Frank and Frank, 1982b).In contrast to these earlier findings, a more recent study that investigated wolf and dog pups across a wider range of ages (between five and eighteen weeks old) reported no discernible performance differences between the two groups during a transparent cylinder task (Salomons et al., 2021).
Only a limited number of studies have explored the cognitive differences between dogs and wolves using a longitudinal approach.For example, Range and Virányi (2014) controlled for developmental effects on animals' social learning abilities.They confirmed that wolves were better imitators of conspecifics at the age of six months than dogs.A subsample of dogs was retested nine months later and the results revealed these dogs had similar cognitive performance as when tested young, suggesting that the developmental stage did not affect dogs' social abilities.
Research on human pointing comprehension provides another compelling example of the importance of longitudinal studies in understanding cognitive development.At the early age of four months, dog pups already exhibit the ability to use momentary distal pointing to successfully find hidden food.In contrast, wolf pups initially struggle with this task and are unable to perform at the same level as dogs.However, after several months of extensive training, the wolves show a remarkable improvement in their performance.Eventually, they can reach a level of proficiency similar to that of dogs in comprehending human pointing cues (Gácsi et al., 2009;Virányi et al., 2008).
While much of the research on differential developmental windows between domesticated and wild animals has focused on canids (Trut et al., 2004;Udell et al., 2010a), there is evidence to suggest that other domesticated species also have divergent developmental trajectories compared to their wild relatives.For example, studies have shown that domestic chickens and guinea pigs engage in more and longer play behavior during development when compared to their wild counterparts.This reinforces that domesticated animals may retain juvenile characteristics for longer periods of time and potentially reach developmental milestones at different ages compared to their wild counterparts (Gabrielle et al., 2022;Kaiser et al., 2015).
Given the lack of longitudinal research in other species, it becomes crucial to approach the current evidence of cognitive differences between domesticated and wild species with caution and bear in mind that evidence from dogs and wolves may not apply to another species.To make informed conclusions, researchers should emphasize the need for more longitudinal investigations across diverse species, broadening our understanding of cognitive development in the animal kingdom.

Methodological issues and cognitive performance
All the confounding factors mentioned above can be considered methodological issues to take into account when studying comparative cognition between domestic species and their relatives.In the following paragraphs, we will focus exclusively on the test setup or context which can potentially influence the cognitive performance of animals.Robert Boice conducted seminal works comparing the learning processes of wild and domesticated rats.While domesticated rats performed better on various learning paradigms, such as conditioning, maze learning, and avoidance learning, compared to their wild counterparts (Bamber and Boice, 1972;Boice, 1981Boice, , 1972;;Hughes and Boice, 1973), Boice acknowledged that critics remained skeptical due to concerns about the ecological validity of tests for wild animals.Domesticated rats evolved in artificial conditions, which may explain why they perform better in artificial testing setups than their wild counterparts.Boice recognized that a "lingering doubt" persisted because wild rats were considered to never be given a "fair test" (Boice, 1981).
The ecological validity of cognitive tests becomes particularly relevant when contrasting results emerge between different studies.In the context of studying cooperation in animals, researchers often employ the cooperative string-pulling task, where two individuals collaborate to pull opposite ends of a string or similar apparatus, aiming to obtain a reward.Notably, two separate studies involving domestic dogs and wolves revealed that wolves demonstrate higher levels of cooperation and success in this task compared to dogs (Marshall-Pescini et al., 2017c), even when one of the two participants has prior experience in the task (Marshall-Pescini et al., 2018).However, a more recent investigation took a different approach by testing cooperation through a problem-solving paradigm simulating a hunting situation.Surprisingly, in contrast to the earlier studies, this research found no significant difference in cooperation between wolves and domestic dogs.The authors propose that their results stem from the fact that the task is more ecologically valid and requires less training than the cooperative string-pulling task.Alternatively, the observed contrasting results could be attributed to the varying complexity of the tasks, with each demanding a distinct level of cooperation (Bräuer et al., 2020b).Such discrepancies emphasize the importance of considering ecological relevance and task complexity when interpreting results from different studies.
Another illuminating case in point comes from studies on the spatial learning of domestic chickens and red junglefowl.Initially, the first experiments evaluated the spatial memory of animals in mazes, where they were tasked with using environmental cues to locate food.However, what researchers overlooked was that the maze design inadvertently allowed the tested individuals to also rely on egocentric cues (based on body position) in addition to environmental cues.As a result, the outcomes led the authors to suggest that red junglefowl were superior spatial learners compared to domestic chickens (Lindqvist et al., 2007(Lindqvist et al., , 2002;;Lindqvist and Jensen, 2009).However, a more recent study, which purposefully eliminated the possibility of birds relying on egocentric cues, presented a nuanced interpretation of the previous results: red junglefowl may indeed excel in spatial learning when utilizing egocentric cues, but when exclusively relying on environmental cues, birds from both origins perform equally well (Ferreira et al., 2022).These results highlight that different approaches to seemingly similar questions may lead to diverse outcomes.
In addition to ecological validity and the test setup, the mere presence of a visible human during testing can also influence the outcomes of a study.In a recent study, Range et al. (2020) examined the differences in self-control between pack-living dogs and pet dogs as compared to the results obtained in a previous study by Brucks et al. (2017).The researchers suggested that the testing methodology played a crucial role in the outcome of the results.Specifically, the pack-living dogs were tested face-to-face with the animal trainers, whereas the pet dogs were tested with the experimenter hidden and not visible.Dogs tend to display submissive behavior towards humans, and this subtle difference in the experimental set-up may have allowed pack-living dogs to exhibit greater self-control in the presence of humans than pet dogs tested without human interaction.The researchers also suggest that the difference in social inhibition between dogs and wolves may be a confounding factor in their study showing that dogs outperform wolves in a delay of gratification task.This is because wolves may exhibit lower self-control in the same test configuration due to their reduced social inhibition towards humans (Range et al., 2020).When wolves are tested in asocial test settings or in the presence of a conspecific, they do as good, and even better, than dogs (Brucks et al., 2019;Marshall-Pescini et al., 2017c, 2015).
Overall, the latest findings underscore the critical importance of researchers being meticulous in their study designs (test setup, ecological validity and contextsocial vs. asocial or natural vs. artificial environments) and interpretations of outcomes.Taking these factors into account can lead to more accurate and comprehensive insights into the cognitive abilities and behaviors of different animal species.

Addressing contradictions and methodological disparities
In the preceding sections, we explored the different pitfalls and limitations that researchers should be mindful of while designing their experiments and interpreting their findings.In the following paragraphs, we present a succinct summary of the essential points that future research should prioritize to enhance our comprehension of cognitive differences between domestic and wild species.However, it is important to recognize that these considerations extend beyond the study of cognition in wild and domestic species; they have the potential to elevate the entire field of animal cognition.
Firstly, it is necessary to allocate more research efforts towards studying the cognitive abilities of a broader range of taxa (Bräuer et al., 2020a).As already discussed, using dogs and wolves as animal models has proven valuable in comprehending the impact of domestication on animal cognition.However, it only provides a partial vision of the domestication/cognition relationship.Between 1998 and 2017, research in the field of cognition predominantly centered around a select few species, such as primates, birds, and canids.However, in recent years, there has been a noticeable shift towards studying a more diverse array of species (Kelly and Lea, 2023).This broadening of focus may have positive implications for more specific scientific inquiries, particularly in understanding cognitive differences between domestic and wild species.Only then can we begin to compare and understanding the contradictions of the experimental results of various species that have undergone similar or different domestication pathways and have been selected in a wide variety of ways.
Secondly, in an ideal scenario, experiments aimed at comparing domestic and wild individuals should employ a longitudinal approach, comparing individuals raised under identical circumstances and with equal levels of experience with humans.Besides that, individuals should only be assessed at the same stages of physical, behavioral, and cognitive development for meaningful comparisons.Meeting all the specified criteria can be challenging.However, this should not deter researchers from pursuing such studies.Instead, it is crucial for researchers to acknowledge that their results may not provide a complete picture of the question they seek to answer.A new and interesting approach to enhance the reliability of studies is to participate in international consortia of researchers, similar to initiatives as ManyDogs or ManyBirds (Lambert et al., 2022;ManyDogs Project et al., 2023).These consortia facilitate the inclusion of large and diverse samples, encompassing variations in age, breed, living environment, temperament, and training history.Standardized procedures adopted by these consortia may lead to more robust and reliable results (McCreary et al., 2023).In a similar manner, researchers exploring comparative cognition in domestic and wild species can facilitate a feasible and meaningful cross-species comparison by joining forces and establishing consistent protocols and analyses.
Finally, in light of the considerations presented above, careful reflection is essential in the implementation of cognitive tests.Researchers must be vigilant in considering alternatives that could potentially explain differences observed between groups of animals.It is crucial to verify that, among other things, domestic and wild individuals are equally habituated to the test environment, have similar levels of neophobia/neophilia, and their responses are not influenced by the presence or absence of the experimenter.By meticulously controlling for non-cognitive factors, researchers can confidently attribute any observed differences to inherent cognitive variations, ensuring that the results accurately reflect the cognitive capabilities of the animals and are not influenced by methodological artifacts.

Brain anatomy and cognitive performance
Since the speculative idea that domesticated animals are cognitively impaired in certain domains, compared to their wild relatives, comes also from a neurobiological perspective, we consider it is important to briefly discuss, in the next paragraphs, some of the common misconceptions (and possible future research avenues) on the comparative study of the neuroanatomy of domesticated animals and their wild counterparts.
As mentioned above, one of the most striking effects of the process of domestication is the reduction in relative brain size (Balcarcel et al., 2022;Ebinger, 1995;Kruska, 1996Kruska, , 1993Kruska, , 1972Kruska, , 1970Kruska, , 2005;;Plogmann and Kruska, 1990).Overall, some domesticated species may have smaller brains, relative to the size of the body, when compared with their wild counterparts (Ebinger, 1995;Kruska, 1996).The difference in the relative brain size between wild and domestic animals, however, can vary greatly among species.For example, while laboratory mice have no obvious change in the relative brain size from their wild counterparts (Frick and Nord, 1963;Kruska, 2005), pigs have a ~34% decrease in the relative brain size when compared with the wild boar (Kruska, 1970(Kruska, , 2005)).By using body size as a "normalizer" for brain size, a practice made popular by Jerison (1973) and then largely used by Kruska (2005), studies on different domestic animals established the idea that the process of domestication is inherently associated with brain shrinking (Ebinger, 1995;Kruska, 1993Kruska, , 2014Kruska, , 2005;;Plogmann and Kruska, 1990).Moreover, this reduction in the relative brain size of domestic strains was further presumed to reflect a decrease in the functional capacity and performance of the brain (Ebinger, 1995;Kruska, 2005).
Although comparing brain size relative to body size has provided great insights into brain evolution and the effects of domestication, it has also brought several disagreements and misinterpretations about it.First, a reduction in the relative brain size does not necessarily mean an actual decrease in the absolute size of the brain.On the contrary, domestic chickens, for instance, have not only larger bodies but also larger brains than their relative, the red junglefowl (Henriksen et al., 2016).The small relative brain size of chickens is due to the fact that body size increases at a much faster rate (+85%) than the increase in brain size (+15%) (Henriksen et al., 2016).Thus, the reduction in the relative brain size of domestic animals does not support the notion that the overall brain size decreases with domestication.Second, it has been shown among different species, including domestic animals, that the evolution of body size and brain size can occur independently at the genetic level (Hager et al., 2012;Henriksen et al., 2016), which is to say that the assumption that "domestication has not affected the dependency of the brain on the body size but has changed the brain size" (Kruska, 2005) might not be entirely correct.Lastly, using overall relative brain size as a proxy for cognition has proven to be inaccurate or at least incomplete, as we discuss below.
Historically, relative brain size has been used as a proxy for cognition and the processing capacity of the brain (Jerison, 1973).The idea that the relative size of the brain reflects cognitive processes is based on the assumption that a larger brain, relative to size of the body, provides extra neural tissue that can be devoted to cognitive tasks (Jerison, 1973).Thus, the finding that domestic animals tend to have relatively smaller brains favored the notion that domestic strains are less cognitively capable (Brust and Guenther, 2015;Ebinger, 1995;Zimen, 1971).The overall relative brain size, however, does not necessarily imply similar brain composition across species.For example, the wild rock dove (Columba livia) and the Saxonian cropper, an ornamental pigeon breed, have approximately similar relative brain masses but quite different brain compositions (Rehkämper et al., 2008).When compared with the rock dove, the Saxonian cropper has a significantly larger optic tectum and mesopallium but a significantly smaller hippocampus (Rehkämper et al., 2008).Given that these brain regions process different functions, one could expect to find differences in the cognitive abilities between the rock dove and Saxonian cropper.In fact, even among domestic breeds, the anatomy and size of different brain regions can differ (Hecht et al., 2019;Rehkämper et al., 2008).Homing pigeons, for instance, have the largest relative size of the hippocampus when compared with other breeds of domestic pigeons (Rehkämper et al., 2008).Because the hippocampus is involved in the processing of spatial cognition, the relative enlargement of the hippocampus in homing pigeons potentially represents a functional adaptation to homing (Rehkämper et al., 2008).In chickens, although domestic strains have smaller relative whole brain size than the red junglefowl, the relative sizes of the telencephalon and cerebellum are larger (Henriksen et al., 2016;Racicot et al., 2021).This difference in the brain composition of domestic chickens is also suggested to represent functional adaptations.For example, it has been recently shown that chickens with larger cerebellum have a better fear memory consolidation than chickens with smaller cerebellum (Gjøen et al., 2023;Katajamaa et al., 2021), further indicating that an increase in the size of the cerebellum may have facilitated domestication in chickens.
Altogether, the results on the brain anatomy of domestic strains reveal that domestication can lead to changes in brain structure and function that are possibly specific to the demands of the domesticated environment.In any case, there is no evidence whatsoever supporting the idea that a relative decrease in the whole brain size of domestic animals reflects an overall decline in cognition.Furthermore, studies on many different mammalian and bird species have shown that there are multiple scaling "rules" between brain mass and numbers of neurons (Herculano-Houzel et al., 2014;Olkowicz et al., 2016).If we assume that neurons are the basic processing unit of the brain, this means that brain size alone might not be as informative in terms of brain processing power as once thought.The incorporation of additional variables beyond whole brain size in future studies, such as neuron number and density of synapses (Olkowicz et al., 2016), will be determinant to gain a more comprehensive understanding of the underlying mechanisms involved in the domestication process, brain evolution, and cognition.

Concluding remarks
The study of domestication and its impact on animal cognition is a valuable area of research that offers significant scientific advantages from both fundamental and applied perspectives.From a fundamental perspective, domestication is considered one of the most significant evolutionary events, providing insight into the genetic mechanisms that led to it.Understanding the consequences of domestication on behavioral, physiological, and morphological traits is also essential to understand the history of human and nonhuman animals.On the practical side, comprehending how domestication has affected an animal's cognition and its ability to adapt to human-made environments is crucial for animal welfare.This knowledge can contribute to better animal management practices, leading to improved animal welfare outcomes (Ferreira et al., 2021;Nawroth et al., 2019).
Our literature review suggests that the effect of domestication on cognitive performance remains unclear.The studies we reviewed had an uneven scope of species and cognitive realms/traits, making it difficult to draw definitive conclusions.Additionally, the results of each study

Table 1
Comprehensive literature search terms.
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Table 2
Comparison of cognitive abilities and performance between wild and domesticated species.The table present information on the specific cognitive realm (physical cognition, social cognition, and general cognition), the cognitive trait investigated, the type of task or test used for each assessment, and the outcomes of the experiments.The outcomes are presented as follows: W > D indicates that wild individuals outperformed their domesticated counterparts; W < D indicates that domesticated animals were superior to wild ones, and W = D indicates that both wild and domesticated individuals performed similarly.
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Table 2
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