Animals

Animal physiology and behavior read as a physical, working version of ideas Ray Peat applied to humans: metabolism, CO2, hormones, and temperature driving longevity, cancer resistance, and regeneration across very different species. This page also covers the relationship between humans and animals directly: health effects of companionship, taming, and communication.

When a person returns to the state in which he was before the Fall, animals again approach him without fear.

— St Paisios

They [animals] regard man as their God, that is why man should love them, because they are not looking forward to another Paradise.

— St. Paisios

The old symbolic pairing, birds as messengers of heaven, reptiles as the fallen and earthbound, tracks a real physiological split. Birds run hot, with a body temperature around 106°F against a mammal's 98°F, and a high metabolism to match; they fly. Lizards are cold-blooded, dependent on the sun or the ground for heat rather than generating their own, and crawl on their bellies.

Cats, dogs, and human health

Domestic cats and several wild felids purr with fundamental and harmonic frequencies concentrated between 25 and 150 Hz, overlapping the specific low-frequency bands (25–50 Hz, with a strong harmonic near 100 Hz) already used therapeutically for bone growth, tendon and ligament repair, and pain and edema reduction. Cats purr when severely injured or frightened as well as when content, which is why some researchers treat the purr as a self-generated healing signal rather than only a contentment display. Peat himself considered the purr unsettled: asked once whether there was anything he didn't know, he answered that he still didn't understand why cats purr, alongside why we yawn.

Dog ownership tracks with a lower rate of disabling dementia in old age. A longitudinal study of Japanese adults over 65 found current dog owners had roughly 40% lower odds of disabling dementia than past or never owners, with the effect concentrated in owners who walked their dogs regularly and were not socially isolated. Dog walkers are far more likely than non-walkers to get regular exercise, and the gut motility and microbial changes that come with regular movement are among the mechanisms proposed for gut-brain axis disruption in Alzheimer's disease. Dog walking also cuts loneliness directly and through the social contact it creates with other people. Cat ownership alone does not show the same dementia protection, consistent with walking and reduced isolation, not pet ownership by itself, doing the work.

Taming and domestication

Playfulness is closely associated with intelligence in mammals and birds, and stress early in life, such as isolation, reduces it.

The idea that an adult animal's nervous system is fixed early and that a wild-caught adult, like a feral cat or dog, "can't be tamed" if it grew up without knowing humans doesn't hold up. People who have taken the time to understand wild animals have found that even those captured as adults can become as sociable as animals raised in domestication from birth, the same empathetic approach demonstrated by the "horse whisperer."

Guardian instinct

Livestock-guardian dogs have repeatedly stayed with their flocks through wildfires that their owners could not outrun. During the 2017 Sonoma County fires, a Great Pyrenees named Odin refused to evacuate with his family and instead herded the household's eight goats, plus several orphaned fawns, into a rock-sheltered clearing; all of the animals, and Odin, survived. During Australia's 2019–2020 bushfires, a kelpie-border collie mix named Patsy herded roughly 900 sheep into the safest paddock on her family's Victoria farm as the fire approached; her owner credited her with saving the flock.

Maternal hormones and predatory instinct

Predation is hard-wired into cats: even well-fed cats keep hunting, since the drive isn't primarily about hunger. Giving birth reverses that around their own young: lactating mothers routinely suppress the same aggressive hunting drive toward their kittens, the one exception being live prey a mother deliberately brings back so the kittens can practice killing it themselves. The shift is hormonal rather than learned. In mice, prolactin acting on a specific hypothalamic circuit (the ventromedial nucleus) actively restrains aggression during lactation, and removing the prolactin receptor from that circuit turns lactating females hyperaggressive again. The same maternal hormone state is strong enough to override species recognition entirely: cats that have just given birth or are still nursing have been documented adopting and nursing puppies, ducklings, and squirrels as though they were their own kittens.

Metabolic rate and longevity

Longevity does not track a slow metabolism; several animals with unusually long lifespans for their size run hot, not cold.

Birds have a higher metabolic rate than mammals of comparable size, live longer, and carry less polyunsaturated fat in their tissues.

Queen bees, which live many times longer than worker bees, have mainly monounsaturated fats in their tissues, while the tissues of the short-lived worker bees, receiving a different diet, within a couple of weeks of hatching will contain highly unsaturated fats.

— Ray Peat

Bats have a very high metabolic rate and an extremely long lifespan for their size, decades rather than the few years typical of small mammals; a high serum CO2 level protects them from the ammonia that accumulates in bat caves. The naked mole rat is another small, long-lived outlier: measured basal metabolic rate is low, but the animals live in closed burrows where CO2 runs from 0.2% to 5%, far above the atmospheric 0.038%, and lab measurements taken outside that high-CO2, high-heat burrow environment may not reflect their real metabolic rate.

A mole rat has never been known to develop cancer. Their serum C-reactive protein is extremely low, indicating that they are resistant to inflammation.

— Ray Peat

Naked mole rat colonies share another trait with beehives: a single reproductive queen, the largest individual in the colony, whose fertility is activated by the high CO2 of the shared burrow or hive. See CO2 for the broader mechanism.

Mice raised with a completely sterile gut, no bacteria at all, live longer on average than normally colonized mice, with a higher proportion surviving to 600 days. Unlike their conventionally raised counterparts, they don't show the usual age-related rise in gut permeability, circulating bacterial products, or pro-inflammatory cytokines, consistent with a large share of the inflammation normally attributed to aging actually coming from a leakier gut barrier and its bacteria, not aging itself.

DHT and morphogenesis

DHT's role is not limited to reproduction. Blocking 5-alpha-reductase, the enzyme that converts testosterone to DHT, with the drugs finasteride or dutasteride disrupts shell development in freshwater snails: embryos grow an elongated, banana-shaped shell instead of the normal tight spiral. Snails do not use DHT for reproduction and lack an androgen receptor, so the effect is not sexual; testing other steroidogenic inhibitors, statins, mutagens, and anti-inflammatory compounds on the same snails produced no shell disruption, singling out the 5-alpha-reductase pathway specifically. This points to a structural, non-reproductive function for DHT common across very distant species, consistent with steroids acting as protective and organizing signals rather than purely reproductive ones. See Androgen.

Thyroid, growth, and metamorphosis

In classic aquarium experiments, tadpoles raised with an added anti-thyroid chemical never turned into frogs; they just kept growing into oversized tadpoles instead, while tadpoles given extra thyroid hormone metamorphosed early into tiny, fully-formed frogs the size of a fly. Thyroid hormone doesn't just drive growth, it drives the energy-dependent differentiation that turns growth into a specific mature form; without it, an organism can keep growing indefinitely without ever finishing development.

Regeneration and hormone response in pets

Ray Peat described treating a friend's pet rabbit that had a brain tumor severe enough that it could no longer stand or hop and that a vet had pronounced beyond help. He rubbed a large dose of topical progesterone oil into the bare skin inside both of the rabbit's ears; it fell into a deep sleep for two to three hours, then woke, stood, hopped to a wall, and urinated out a large volume of retained fluid before recovering full mobility. The rabbit's extreme relaxation matches a picture in Hans Selye's 1947 endocrinology textbook of a researcher holding a rat so completely relaxed under stress that it looks dead.

In a separate account, a friend's dog lost an eye in a fight, leaving only a red socket. Put on a fresh goat milk diet, a small eye reappeared in the socket within a couple of weeks and had normal vision within several more, the same air-excluded, high-CO2 wound environment lets a severed fingertip regrow.

Animal communication and consciousness

Peat described talking to snakes and ants on his property, telling them to stay away or leave, and reported that they did: he said he'd seen only one or two snakes in 25 years in Texas after adopting the habit, and that ants he'd spoken to in the same way left the house.

A 2005 Scotland study gave chimpanzees and 3-year-old children the same box-opening task. The chimpanzees solved it in flexible, varied ways; the children more often reproduced whatever specific method they'd seen demonstrated, even when a more direct route was available. The researchers suggested this was because children are more susceptible to cultural convention, not because they are more intelligent than the apes. This contradicts the doctrine that animals "use instinct rather than intelligence" and lack a capacity for generalization; the same ideology leads people to interpret animal behavior that clearly demonstrates understanding as mere mimicry or conditioning.

A chicken embryo's brain normally stops growing when the glucose stored in the egg runs out. Researcher Zamenhof opened chicken eggshells at exactly that point in development and added glucose directly; the brain kept growing, producing chickens with bigger brains than the "genetics of the chicken" was supposed to allow. Brain size and intelligence in that experiment tracked available energy, not a fixed genetic ceiling.

A common form of the same claim is that dogs and other animals respond only to a speaker's intonation, not the meaning of the words themselves. An fMRI study of dogs listening to their trainers found the opposite: word meaning and intonation are processed in separate hemispheres, meaning and praise words in the left, intonation in the right, and then combined, since praise words only activated the dog's reward circuitry when they were also said in a praising tone. The neural separation of word meaning from intonation isn't uniquely human. A similar case turns up decades earlier: early researchers working with a porpoise were surprised when it understood a sequence of one tone, then two, then three, and answered by producing a series of four tones of its own, meaning the porpoise had inferred that the researchers were counting.

• Talking to them: Conversations with ravens and other animals
• God created multiple languages as punishment for man's pride
• Children intuitively speak to animals as equals; this is usually lost with age but sometimes retained in old age.
• Japanese folklore ("lost cat method"): asking stray cats for help with details of a missing cat often results in its return.
• Ravens' singing, vocal fine-tuning, and greetings are intrinsically meaningful, self-rewarding, and context-appropriate, not mere mimicry.
• Culture arbitrarily partitions consciousness, language, and comprehension among living beings.
• Many human utterances are incoherent mumbling with limited vocabulary, worse than some animal communication (e.g., Koko, kitten meows).

Birdsong and the nervous system

Recorded birdsong measurably lowers anxiety, depression, and paranoia in healthy adults: a randomized online trial of nearly 300 participants found just six minutes of birdsong audio significantly reduced anxiety and paranoia compared to traffic noise, with the effect strongest for a variety of species singing together rather than one or two. A separate study of over 1,000 participants found that hearing or seeing birds improved mental well-being for up to eight hours afterward.

For nearly all of human history, background birdsong would have been constant except during an active threat, a predator, a storm, a fire, that silenced it; its absence may have functioned as a danger signal long before humans had words for one. This is a plausible reading of why the sound still calms the nervous system today, but it hasn't been tested directly and no primary source connects the two; treat it as a hypothesis, not an established mechanism.

Plant sensation

• J.C. Bose first demonstrated plants' complex immune/sensory systems using his crescograph to record responses to stimuli (light, touch, injury).
• Plants lose their leaf-closing response to touch when exposed to lidocaine. Weigl (1968), Zeitschrift fur Naturforschung.
• Lidocaine applied to roots blocks shoot movements in plants. Yokawa et al. (2017), Annals of Botany (doi:10.1093/aob/mcx155).
• Plants increase stress hormones when exposed to insect-feeding vibrations. Body et al. (2019), Front Plant Sci (doi:10.3389/fpls.2019.00810).
• Plants produce sweeter nectar within minutes when played recordings of pollinating bee wingbeats. Veits et al. (2019), Ecol Lett.

Peaty animals

Bee

A queen and a worker bee hatch from genetically identical eggs; the difference is diet. Worker larvae are fed plain pollen and nectar, while a queen larva is fed royal jelly, and that diet difference alone determines which caste she becomes. Royal jelly works epigenetically: its active compounds inhibit DNMT3A, an enzyme that methylates DNA, and HDAC3, an enzyme that strips activating marks off histones, and blocking both keeps the genes for ovary development and long life switched on in the queen instead of silenced.

That diet difference compounds with a second one: CO2. Worker bees leave the hive daily to forage, breathing ordinary outside air, while the queen stays inside a hive whose CO2 the workers actively regulate, keeping it as high as 5–6%, similar to a naked mole rat burrow. One calculation put queen bees at roughly 47 times the lifespan of workers. Ray Peat attributed most of that gap to the workers' constant exposure to atmospheric oxygen combined with the PUFA in the pollen they eat, which without the queen's high CO2 readily turns into lipid peroxides; in one experiment, tripling tissue CO2 dropped lipid peroxide levels to zero. A high CO2 hive environment also activates the queen's ovaries directly, the same fertility mechanism as the naked mole rat's burrow, above.

Albatross

Albatrosses can spend years at sea without touching land, and drink seawater directly. A pair of salt glands near the nostrils pulls the excess sodium out of the bloodstream and excretes it as a concentrated brine, released through the nostrils, often with a forceful head shake. Ray Peat pointed to the salt gland as the clearest case that sodium export isn't just a "membrane pump" doing simple diffusion: "carbon dioxide is the driving force in the salt gland. The constant formation of CO2, and its loss into the air, allows a high concentration of salt to be excreted. Blocking the interchange of CO2 and carbonic acid...prevents the excretion of salt." That argument, that the more extreme an "active transport" process looks, the more it points to something other than a membrane pump, is the same one Gilbert Ling made about ion distribution generally.

Cockatoo

Sulphur-crested cockatoos are among the longest-lived birds: the best-documented record is 57 years (a captive bird named Cocky, at London Zoo), and anecdotal, unverified claims of cockatoos living past 80 or even 100 are common but not independently confirmed. Like birds generally, they run a body temperature around 106°F with a resting heart rate in the hundreds of beats per minute, far higher than a similarly sized mammal. Long-lived birds tend to keep highly peroxidizable PUFA out of their mitochondrial membranes: seabirds with roughly 3.8-fold greater predicted longevity than domestic fowl have a significantly lower peroxidation index in their heart membrane lipids. The pattern doesn't hold across all birds equally; a broader 2021 analysis found no consistent relationship between membrane fat composition and lifespan once more species were included, so treat it as a real but incomplete piece of the story, not a settled rule.

Flamingo

Flamingos wade all day in hot, salty water and eat the algae growing in it. Ray Peat pointed to flamingo specialist Leslie Brown's suspicion that they could live to 130 as an illustration of temperature and fat saturation: at the high temperature of that water, an algae that made PUFA would have it oxidize immediately, so the algae make saturated fats instead, and the flamingos eating them are shielded from the same PUFA-driven aging Peat attributes to most modern diets. The verified longevity record is far short of that: the oldest documented flamingo, a Greater Flamingo at Adelaide Zoo, lived to about 83; Brown's 130-year figure was speculation, not a measured lifespan.

Amazon fish

Fish from the warm Amazon (75–85°F) have fat that runs about 97% saturated, similar to butter, the same warm-water logic as the flamingo's algae. Cold-water fish need the opposite: unsaturated fat stays liquid at low temperatures, which is why fish from cold water are the PUFA-richest in the first place.

Shark

Sharks rarely develop cancer. Geneticist Leonell Strong, who bred the cancer-prone mouse strain Ray Peat used in his own early estrogen research, found that injections of shark liver extract prevented breast cancer in those mice, and took it as evidence that cancer is a product of genetic instability, since sharks are an old, genetically stable lineage. But extracts of other animals' livers worked just as well, pointing instead to a liver factor needed to clear excess estrogen, not anything specific to sharks' genetics.

Salmon

Salmon reverse their thyroid/prolactin balance depending on which direction they're swimming. A young salmon leaving fresh water for the ocean needs to tolerate a much saltier environment, and its thyroid hormone surges as it makes the transition; a mature salmon returning to fresh water to spawn shows the opposite shift, a sharp rise in prolactin. Ray Peat used this as a template for reading human water and salt retention: a hypothyroid person, who tends to lose salt and retain water, is physiologically closer to the salmon that has just returned to the river.

Torpor and PUFA

Hibernation is a deliberate slowdown of metabolism, and animals prepare for it by stocking their tissues with PUFA beforehand. Researchers have been able to induce torpor experimentally just by feeding animals PUFA; feeding them sugar instead of unsaturated fat keeps them from going into it. Ray Peat treated menopausal hot flashes as touching the same system in reverse: high-dose estrogen lowers metabolism toward a hibernation-like state and blocks sweating, while a large dose of carbohydrate at bedtime, replenishing liver glycogen, controls hot flashes without the metabolic slowdown.

Octopus

A mother octopus stops eating after laying her eggs and wastes away, usually dying around the time they hatch. The trigger is hormonal: her optic gland, a structure similar to the pituitary, undergoes a major shift in cholesterol metabolism after she reproduces, driving up several steroid hormone pathways. Surgically removing the optic gland reverses the whole sequence, the mother abandons her eggs, resumes eating, and can even mate again, confirming the gland is what drives the self-destruction rather than exhaustion or starvation alone. Steroid signaling ending an organism's life on a fixed hormonal schedule rather than gradual wear is the same pattern as salmon death after spawning, above.

Whale

Only a handful of species are known to go through menopause: humans, orcas, belugas, narwhals, and pilot whales. In orcas, decades of demographic data show that grandmothers past their own reproductive years measurably raise their grandcalves' survival odds, and that when a mother and daughter breed at the same time, the older female's calves die at nearly twice the rate of the younger female's, a real reproductive cost to staying fertile once a daughter is also breeding. The "grandmother hypothesis" reads orca menopause as favoring redirected, non-reproductive parental investment once the returns from further reproduction turn negative.

Elephant

Elephants have far more cells than humans, and cells dividing more times should mean more chances for a cancerous mutation to take hold, yet elephants get cancer at a lower rate than humans do, a mismatch known as Peto's paradox. Elephants carry roughly 20 copies of the tumor-suppressor gene TP53, compared to a single copy in humans and most other animals; those extra copies drive a more aggressive damage response in elephant cells, which are more prone to self-destructing when DNA damage occurs, before it has a chance to become a tumor.

Crow

Ray Peat linked bird longevity to brain size and how developed a chick is at hatching: birds like owls, parrots, and crows hatch dependent and underdeveloped and keep growing their brains afterward, and end up both smarter and longer-lived than birds like chickens that hatch mobile and self-sufficient. As an example, he cited a pet crow named Tata that lived to 59 in New York, noting that parrots sometimes live past 100. Crows also form real, individual relationships with people: an 8-year-old girl in Seattle who fed the crows in her yard for years began receiving small gifts in return, over 100 of them, documented by date and location, including a camera lens cap her mother had lost, found cleaned and left at a birdbath, caught on video being delivered by a crow.

See also

• CO2
• PUFA
• Thyroid
• Progesterone
• DHT
• Longevity
• Menopause
• Loneliness
• Dementia
• Exercise
• Gilbert Ling
• Hans Selye
• Ray Peat