なぜ人類は「役に立たない動物」を愛するのか【進化心理学】
考えすぎる葦
107,768 views
Aren't we being cleverly manipulated?
Did you know that in this country, there are more pet dogs and cats than children under 15? They don't generate any wealth, nor do they carry our genes forward.
Yet, we pay 100% of their medical expenses, which aren't covered by insurance, and when they die of old age, we build graves and shed tears. However, right next to that warm living room, in the kitchen, there are slices of pork. Pigs are just as intelligent as dogs. What determined their fate wasn't their ability or their sensitivity to pain, but simply which "framework" we placed their lives in.
A very similar scene exists in nature. A parent bird, whose nest has been taken over by a cuckoo and who has lost all its offspring, diligently continues to feed insects to the offspring of another bird, many times its own size. That parent bird isn't raising the other bird out of love. It's simply being stimulated externally by the "nurturing switch" in its brain through the signal of its calls. Dogs activate a perpetual motion machine of oxytocin by gazing into human eyes, and cats subtly incorporate the frequency of a baby's cry into their soothing purring. Moreover, it is none other than ourselves who have reshaped their faces to resemble babies. Three conditions for "brood parasitism"—forcing parenting onto others—are met without resistance, at least two of them.
But the moment we apply the last condition—"the host suffers decisive harm"—this brilliant hypothesis crumbles beneath our feet. 78.7% of pet cats and 58.3% of pet dogs in Japan have been spayed or neutered. It wasn't us who were deprived of the opportunity to reproduce, but the animals we supposedly love.
So why do humans love animals that seem so useless? This time, we've explored the reasons why humans keep pets from the perspectives of behavioral ecology and neuroscience.
----------------------------
▼Timestamps
00:00 - Prologue: A Country with More Dogs and Cats Than Children
02:22 - Chapter 1: My Beloved Cat and Pork
06:58 - Chapter 2: The Perpetual Motion Machine of Emotion
11:55 - Chapter 3: The Boundaries of Egoism
16:20 - Chapter 4: The Noblest, Most Fragile Wiring
20:43 - Epilogue: The Clumsy Mannerism of Love
----------------------------
▼References and Data Sources
[1] Japan Pet Food Association, "National Dog and Cat Ownership Survey" (6.79 million dogs, 9.15 million cats, total 15.95 million) / Statistics Bureau of the Ministry of Internal Affairs and Communications, "Population Estimates" (Population under 15 years old: 13.66 million).
[2] NAPHIA (North American Pet Health Insurance Association) "State of the Industry Report 2025" (7.03 million pets in North America are insured. Premiums paid in 2024 amounted to $5.2 billion).
[3] Japan Pet Food Association (The market size for dog and cat food in Japan is approximately 460 billion yen annually).
[4] Ministry of Agriculture, Forestry and Fisheries "Livestock Product Distribution Survey" 2024 Final Report (Total number of pigs slaughtered nationwide: 16,259,000). *This is a different concept from "number of animals shipped" and "carcass production volume," and represents the number of animals processed at slaughterhouses for consumption.
[5] Davies, N. B., Kilner, R. M., & Noble, D. G. (1998). "Nestling cuckoos, Cuculus canorus, exploit hosts with begging calls that mimic a brood of many young." Proceedings of the Royal Society B, 265(1397), (University of Cambridge. A single cuckoo chick increased its food intake by making calls that mimicked multiple chicks begging simultaneously.)
[6] Nagasawa, M., et al. (2015). "Oxytocin-gaze positive loop and the coevolution of human-dog bonds." Science, 348(6232), 333-336. (Azabu University. A reciprocal loop was observed where the more a dog gazed at its owner, the higher the owner's oxytocin levels became, and the dog's oxytocin levels also increased when petted. This same loop did not occur between humans and wolves raised by humans.)
[7] McComb, K., Taylor, A. M., Wilson, C., & Charlton, B. D. (2009). "The cry embedded within the purr." Current Biology. (University of Sussex. The purring of cats begging for food contains high-frequency "crying" components that are difficult for humans to ignore.)
[8] Baby schema (Kindchenschema) = a concept by Konrad Lorenz. "Supernormal stimulus" = a concept by Niko Tinbergen. The phenomenon in which a stronger response is elicited from a fake object with exaggerated characteristics than the real thing.
[9] Japan Pet Food Association, "2025 National Survey on Dog and Cat Ownership" (Spaying/Neutering Rate: Dogs 58.3% (n=1,260), Cats 78.7% (n=967))
[10] Herzog, H. (2011). "The impact of pets on human health and psychological well-being: Fact, fiction, or hypothesis?" Current Directions in Psychological Science, 20(4), 236-239. (Regarding the health effects of pet ownership, there is data showing both positive and negative effects, and a scientific conclusion has not yet been reached.) / Herzog, ...
20 Comments
犬なんて犬小屋で飼うもん、猫は好き勝手出入りするしご近所で世話するもん、という田舎の価値観で育った私は、
就職してから飼い主がうちの子うちの子言うのが理解できなくてしばらく本気で苦しんだ。
可哀想可哀想って人間が囲えば囲うほどにどんどん自分で自分の生命を何とかしなくなるしすぐ病気になる。
そんな風に見えました。
大学の最初の授業で言われましたね、
動物は人間との関係でこう分類します。
愛玩動物・産業動物・展示動物・野生動物・実験動物
さぁ、あなたはどの動物を扱う職に就きたいですか、と。
愛玩動物獣医師の仕事の本質は、わんちゃん猫ちゃんを救うことよりも、満たされない人間の心を救うことです。
人間の他にも、チンパンジー、ゴリラ、オランウータンなどの霊長類やラングールなどの旧猿類、更にはオオカミやライオンなどの食肉目、魚やクモ類にいたるまで多くの種でこの”ペットを飼う”という行動が報告されています(私の感想では双利共生との境界性が若干微妙な例もあります)。
なぜ人類は「役に立たない動物」を愛するのか【進化心理学】
考えすぎる葦
107,768 views
Aren't we being cleverly manipulated?
Did you know that in this country, there are more pet dogs and cats than children under 15? They don't generate any wealth, nor do they carry our genes forward.
Yet, we pay 100% of their medical expenses, which aren't covered by insurance, and when they die of old age, we build graves and shed tears. However, right next to that warm living room, in the kitchen, there are slices of pork. Pigs are just as intelligent as dogs. What determined their fate wasn't their ability or their sensitivity to pain, but simply which "framework" we placed their lives in.
A very similar scene exists in nature. A parent bird, whose nest has been taken over by a cuckoo and who has lost all its offspring, diligently continues to feed insects to the offspring of another bird, many times its own size. That parent bird isn't raising the other bird out of love. It's simply being stimulated externally by the "nurturing switch" in its brain through the signal of its calls. Dogs activate a perpetual motion machine of oxytocin by gazing into human eyes, and cats subtly incorporate the frequency of a baby's cry into their soothing purring. Moreover, it is none other than ourselves who have reshaped their faces to resemble babies. Three conditions for "brood parasitism"—forcing parenting onto others—are met without resistance, at least two of them.
But the moment we apply the last condition—"the host suffers decisive harm"—this brilliant hypothesis crumbles beneath our feet. 78.7% of pet cats and 58.3% of pet dogs in Japan have been spayed or neutered. It wasn't us who were deprived of the opportunity to reproduce, but the animals we supposedly love.
So why do humans love animals that seem so useless? This time, we've explored the reasons why humans keep pets from the perspectives of behavioral ecology and neuroscience.
----------------------------
▼Timestamps
00:00 - Prologue: A Country with More Dogs and Cats Than Children
02:22 - Chapter 1: My Beloved Cat and Pork
06:58 - Chapter 2: The Perpetual Motion Machine of Emotion
11:55 - Chapter 3: The Boundaries of Egoism
16:20 - Chapter 4: The Noblest, Most Fragile Wiring
20:43 - Epilogue: The Clumsy Mannerism of Love
----------------------------
▼References and Data Sources
[1] Japan Pet Food Association, "National Dog and Cat Ownership Survey" (6.79 million dogs, 9.15 million cats, total 15.95 million) / Statistics Bureau of the Ministry of Internal Affairs and Communications, "Population Estimates" (Population under 15 years old: 13.66 million).
[2] NAPHIA (North American Pet Health Insurance Association) "State of the Industry Report 2025" (7.03 million pets in North America are insured. Premiums paid in 2024 amounted to $5.2 billion).
[3] Japan Pet Food Association (The market size for dog and cat food in Japan is approximately 460 billion yen annually).
[4] Ministry of Agriculture, Forestry and Fisheries "Livestock Product Distribution Survey" 2024 Final Report (Total number of pigs slaughtered nationwide: 16,259,000). *This is a different concept from "number of animals shipped" and "carcass production volume," and represents the number of animals processed at slaughterhouses for consumption.
[5] Davies, N. B., Kilner, R. M., & Noble, D. G. (1998). "Nestling cuckoos, Cuculus canorus, exploit hosts with begging calls that mimic a brood of many young." Proceedings of the Royal Society B, 265(1397), (University of Cambridge. A single cuckoo chick increased its food intake by making calls that mimicked multiple chicks begging simultaneously.)
[6] Nagasawa, M., et al. (2015). "Oxytocin-gaze positive loop and the coevolution of human-dog bonds." Science, 348(6232), 333-336. (Azabu University. A reciprocal loop was observed where the more a dog gazed at its owner, the higher the owner's oxytocin levels became, and the dog's oxytocin levels also increased when petted. This same loop did not occur between humans and wolves raised by humans.)
[7] McComb, K., Taylor, A. M., Wilson, C., & Charlton, B. D. (2009). "The cry embedded within the purr." Current Biology. (University of Sussex. The purring of cats begging for food contains high-frequency "crying" components that are difficult for humans to ignore.)
[8] Baby schema (Kindchenschema) = a concept by Konrad Lorenz. "Supernormal stimulus" = a concept by Niko Tinbergen. The phenomenon in which a stronger response is elicited from a fake object with exaggerated characteristics than the real thing.
[9] Japan Pet Food Association, "2025 National Survey on Dog and Cat Ownership" (Spaying/Neutering Rate: Dogs 58.3% (n=1,260), Cats 78.7% (n=967))
[10] Herzog, H. (2011). "The impact of pets on human health and psychological well-being: Fact, fiction, or hypothesis?" Current Directions in Psychological Science, 20(4), 236-239. (Regarding the health effects of pet ownership, there is data showing both positive and negative effects, and a scientific conclusion has not yet been reached.) / Herzog, ...