1. Introduction
Dogs and cats are the most influential and successful pets [
1,
2,
3]. Despite ongoing debates about the time and place of dogs’ origin [
4,
5,
6], it is widely accepted that dog was probably the first domesticated animal [
7]. They have been companions to humans for at least more than 15,000 years, according to the archaeological record, and even longer, according to genome analysis [
8,
9,
10] Cats have a relatively shorter history of domestication, with evidence supporting a timeline dating back to 9,500 years ago [
11,
12]. Still, both dogs and cats hold an important place in humans’ hearts and lives. According to the latest survey of the American Pet Products Association (APPA), approximately 49% of households in the United States own dogs, and 35% of households own cats in 2023-2024, far exceeding the ownership of ornamental fish, which ranks third with the proportion of 10%. Humans are so attached to dogs and cats that they are willing to lavish much affection, time and money on their pets, even though this investment does not directly benefit their fitness [
13,
14,
15]. Researches indicate that dog and cat owners view their pets as family members [
16,
17,
18]. Even to some extent, dogs and cats can occupy social positions similar to those of partners [
19,
20] and children [
21] in the home.
Why humans are so attached to dogs and cats remains a long study question, and it was one of the 125 scientific questions jointly published by Shanghai Jiao Tong University (SJTU) and the journal of ‘Science’ (Biology: Why do humans get so attached to dogs and cats?) in 2021. Previous studies have offered some explanations for this question. Dogs and cats may first be domesticated for functional roles such as hunting, herding and protecting food from rodents [
22,
23] and still be kept for practical purposes in modern life. On the other hand, some people keep dogs or cats since they can offer social, physical and psychological support. Dogs and cats may provide similar companionship as family members [
19,
20,
21,
24]. In addition, numerous researches have shown that they can relieve people’s mental stress, improve emotional well-being and provide therapeutic support [
15,
25,
26,
27,
28,
29,
30]. Human preferences for dogs and cats may also be influenced by genetic variations. A study on twins showed that the heritability of dog ownership is high in both genders (57% for women and 51% for men) [
31]. Apart from those, there are other factors that may affect human preferences for dogs and cats, such as gender, age or individual income. For instance, it is widely accepted that women tend to be more compassionate and exhibit stronger attachment behaviors, affect and caregiving than men [
32,
33]. Younger adults have higher cognitive empathy than older adults [
34,
35], which may make them more attached to dogs and cats. While age and wealth may determine how much energy, time and money a person can devote to dogs and cats and thus affect the degree of preferences [
14].
Though many studies have attempted to explain why humans get so attached to dogs and cats, most of them mainly focus on one single factor and lack generality. To better answer this question, a more comprehensive and systematic investigation is required, especially its current situation and potential influencing factors. Given that humans have developed a variety of preferences, such as games and music, it is necessary to determine to what extent humans currently prefer dogs and cats compared to other forms of entertainment and how different factors influence that preference. Here, we used data from online video platforms and anonymous questionnaires to get a more comprehensive and systematic overview of the human preferences for dogs and cats. We aimed to 1) obtain the current situation of human preferences for dogs and cats and 2) investigate what factors could influence human preferences for dogs and cats and how strong an impact they have. We first evaluated how much humans prefer dogs and cats by investigating how much more they prefer videos about dogs and cats compared to other videos on other topics. Then, we calculated the heritability of people’s preferences for dogs and cats based on the information about dog and cat ownership of the questionnaire respondents and their family members. Meanwhile, we investigated the main reasons why they chose or planned to have dogs or cats. Finally, we verified the potential factors (i.e. age, gender, individual income, psychological factors) that may have an effect and the extent of their impact by analyzing the basic information of video audiences and questionnaire respondents. Specifically, we posited that young people, women, and those with high incomes were likelier to keep dogs and cats than older people, men, and those with lower incomes.
4. Discussion
While previous studies have provided some explanations for why humans are so attached to dogs and cats, a more comprehensive and systematic overview of the human preferences for dogs and cats is required. Using three independent datasets (i.e., Bilibili videos, online questionnaires and Douyin (Tik Tok) videos, we found that humans prefer videos that include dogs and cats to most other subjects (
Figure 1); there is significant heritability of owning either a cat or dog or both (
Figure 2); and gender, age and economic development impacted the audience's preferences significantly (
Figure 4,
Table 1). Overall, our study highlights the current situation and influencing factors of human preferences for dogs and cats.
Surveys have compared the proportion of households of dogs and cats with other pets [
38,
39,
40,
41,
42]. However, few studies try to compare the level of preferences for dogs and cats with other preferences in modern life. In this study, using the dataset of online videos (i.e., Bilibili videos), we found that, both the number and the growth trend, preferences for dogs and cats are relatively high compared to other types of preferences such as games and music (
Figure 1,
Figure S1). This pattern gives us a more comprehensive picture of the current situation of human preferences for dogs and cats. Moreover, the results also confirmed that humans are indeed attached to dogs and cats [
43,
44]. Since that the results here were based on online videos, they might not totally reflect the situation of daily life. For instance, most people might be biased toward games, fun videos, and movies that only exist virtually online. This might underestimate the degree of preferences for dogs and cats. Another confusing factor that needs to be considered is that people with dogs or cats in daily life might be less frequently on the internet (e.g., they have to look after their pets). In this respect, future studies directly investigating the situation of preferences for dogs and cats in daily life are more appealing.
In this study, we found a significant heritability of owning either a cat or dog or both (
Figure 2). Our findings align with a recent study showing that the heritability of dog ownership was 0.51 for men and 0.57 for women [
31]. These similarities between the current and previous studies indicate that human preferences for dogs and cats are influenced by genetic variations and potentially under selection [
45,
46]. Furthermore, for the reasons of having a dog or a cat or both, previous studies showed that functional roles and companionship are the two main reasons [
47,
48,
49,
50,
51]. Yet, these studies did not compare the relative importance of these reasons simultaneously or within a study. In our study, we have listed five main reasons at the same time and evaluated their relative importance. We found that keeping dogs and cats to obtain emotional support accounted for the largest proportion (85.8%), followed by treating dogs and cats as tools (41.3%), health (31.6%), following the popular trend (25.2%) and religious or cultural issues (6.1%) (
Figure 3). These new results offered new insights into the research of human attachment to dogs and cats. In the initial stages of the relationship between humans and pets, the primary consideration was the functional roles of dogs and cats. Historically, dogs assisted humans with hunting, guarding and protection [
52,
53,
54,
55,
56], while cats helped humans by protecting food supplies [
57,
58]. However, as societal productivity developed, the need for emotional companionship gradually became the main reason for humans to keep dogs and cats [
59,
60]. This shift highlights a dynamic process of human preferences for dogs and cats, reflecting an evolutionary change from practical utility to emotional appreciation, which is an interesting and valuable research topic and deserves further study.
In addition to genetic variations, other potential factors may affect human preferences for dogs and cats, such as gender, age or individual income. Generally, we found that women, younger people, and those with higher income had stronger preferences for dogs and cats compared to men, older ones and people with lower income (
Table 1,
Figure 4). Additionally, our findings reveal that humans show a higher level of interest in dogs compared to cats (
Table 1 and
Figure 4a), which corresponds with the current status of dogs being the most popular pets (33.4% of households owned dogs, and 22.5% owned cats) [
39]. In previous studies, how different factors affect human preferences for dogs and cats has not yet come to a unified definition. Our findings (
Table 1 and
Figure 4b,c) align with a recent study reported by Fraser showing that younger people and women are more likely to be pet owners in New Zealand [
61]. Similarly, some studies support the notion that women have stronger preferences [
62,
63,
64], while a few suggest that men have stronger preferences [
65]. These discrepancies may be attributed to regional differences, with varying cultural traditions potentially influencing the results. Still, it is important to note that since our data source is online videos, differences in the ability of different age groups to access the Internet may affect our estimates of their preferences. For example, the preferences for dogs and cats may be underestimated among elders who use the Internet less and minors who are primarily restricted from using the Internet. When it comes to individual income, we found that regional GDP was positively correlated with the number of comments. This is similar to the positive correlation between the number of pets and the GDP of different states in the USA (data from Wiki). Higher income levels likely make it more feasible to afford the costs of owning dogs and cats. People living in a relatively more developed area may also find it easier at work and have more leisure time to keep a dog or cat in real life [
66]. In summary, each factor that affects the degree of human preferences for dogs and cats might not be independent of each other, and different research methods may also lead to different conclusions.
In this study, we did not consider the morphological or psychological traits of the animals, such as appearance, age and personality, because they are difficult to quantify from the videos. Previous studies have shown that the traits of dogs and cats can also influence human preferences for them. For instance, several research indicated that the appearance of dogs is the main factor that highly influences people’s decisions to buy or adopt them [
67,
68,
69]. Humans may choose some features that are thought to be associated with an infantile aesthetic, such as bigger eyes and a larger space between the eyes [
70]. Also, dogs that can enhance paedomorphism (change the eye size and height by raising the inner brow) through greater facial flexibility are found to be more desirable to humans [
71]. Additionally, the animal’s age also potentially affects people’s decisions on whether or not to have a dog. According to the research by Brown [
72], the length of a dog's stay in a shelter increases with its age, which means the older the dog is, the less likely it is to be adopted. Similarly, studies conducted in Australia and Italy find that the public tends to acquire a dog as a puppy [
73,
74]. This tendency may be associated with the preference for infantile-like features, the opinion that a puppy can be trained to acquire good habits, or just because the owner wants to experience the “puppy stage” of a dog’s life [
68]. Apart from this, researchers also find that how animals behave when interacting with humans can affect human attachment to pets, which we cannot fully study in our work with online videos and questionnaires. A study by Protopopova and Wynne [
75] shows that dogs that are willing to respond to potential adopters are more likely to be adopted. Similar studies have also found that a dog's temperament and its behavior during interactions with people can influence human attitudes toward them [
69,
74]. In short, future work that considers these aspects (i.e., the traits of pets and their social behaviour) in conjunction with the characteristics of the owners (such as personality, gender, age, and economic status) could provide a more thorough understanding of factors that influence human preferences for these pets.
Human preferences for dogs and cats are never one-sided. This interesting question involves a complex interplay of evolving human tastes, the selection of various dog and cat breeds, the dynamic characteristics of these animals, and their impact on people. On the one hand, humans selectively breed dogs and cats according to their own preferences and needs, even if certain traits can lower individual fitness. For example, Scottish Fold cats with osteochondrodysplasia [
76] and French Bulldogs, which are more prone to health issues than other breeds [
77], are still being chosen by humans. On the other hand, some believe that cats and dogs change their ancestral behaviors to function as social releasers, eliciting human parental care [
13] and may thus gain higher fitness. In summary, this is a co-evolutionary process of mutual selection. However, research in this area is still lacking, particularly in co-evolutionary model construction and simulations. Using comprehensive mathematical simulations and models can delve deeper into the impact of human behavior on the evolution of dogs and cats. We should emphasise these aspects more, as they will help us understand how humans and dogs and cats have influenced each other throughout their long companionship, and why humans are so attached to these animals.