Animals lick their newborns for several critical reasons: to clean them, stimulate their bodily functions, form a chemical bond, and, perhaps most remarkably, to shape how their offspring will handle stress for the rest of their lives. What looks like a simple grooming habit is one of the most powerful parenting behaviors in the animal kingdom, with effects that reach all the way down to gene expression.
Cleaning and Immediate Survival
The first licks a newborn receives serve the most obvious purpose. Mothers lick away the amniotic fluid and birth membranes that cover their young, clearing the nose and mouth so the baby can breathe. In prey animals like deer and rabbits, this cleaning also removes scent traces that could attract predators. A fawn still wet with birth fluids is a beacon for wolves and coyotes, so a doe will lick her newborn thoroughly and even consume the placenta to eliminate odors from the birth site.
Licking also stimulates circulation and body warmth. Newborn mammals, especially small ones like kittens and puppies, can’t regulate their own body temperature well. The physical friction of a mother’s tongue promotes blood flow to the skin and helps dry the fur, both of which reduce the risk of hypothermia in those first vulnerable hours.
Stimulating Digestion and Elimination
Many newborn mammals physically cannot urinate or defecate on their own. Their nervous systems aren’t mature enough to trigger those reflexes independently. The mother’s licking of the belly and genital area provides the mechanical stimulation needed to get the digestive and urinary systems working. Without it, a newborn puppy, kitten, or rodent pup can develop dangerous bloating or waste buildup. This is why orphaned animals raised by humans need to be gently rubbed with a warm cloth after feeding, mimicking the mother’s tongue.
Bonding Through Scent and Oxytocin
Licking is how many animal mothers learn to recognize their own young. Sheep, for example, must lick their lambs within the first few hours after birth or they may reject them entirely. The act of licking exposes the mother to her newborn’s unique scent profile, locking in a chemical identification system that lets her pick her own lamb out of a crowded flock.
This bonding is driven in large part by oxytocin, sometimes called the “hormone of attachment.” Oxytocin floods the mother’s brain during birth and nursing, and the physical contact of licking keeps those levels elevated. Higher maternal oxytocin levels are significantly linked to more affectionate contact behaviors following mother-infant interaction. The hormone works on the infant’s brain too, directing the newborn to preferentially seek out social cues from its own species and form its first attachment. In prairie voles, pups that received licking and grooming from both parents showed a greater ability to bond socially later in life compared to those raised by a single parent.
Programming the Stress Response for Life
This is where the science gets genuinely surprising. The amount of licking a newborn receives doesn’t just affect its first days. It changes how the animal’s brain responds to stress for the rest of its life, and the mechanism is epigenetic, meaning licking actually alters how certain genes are expressed without changing the DNA itself.
The most detailed evidence comes from decades of rat studies. Rat mothers naturally vary in how much they lick and groom their pups, and this variation is remarkably stable across multiple litters. Pups raised by high-licking mothers grow into adults with more receptors for stress hormones in the hippocampus, a brain region critical for memory and emotional regulation. Those extra receptors act like a better braking system: when stress hormones spike, the brain detects them faster and dials the response back down more efficiently. The result is an adult animal that handles novelty and challenge with relative calm.
Pups raised by low-licking mothers develop the opposite profile. As adults, they show heightened stress reactivity across the board: stronger startle responses, less willingness to explore new environments, and longer hesitation before eating food in an unfamiliar setting. They also engage in more aggressive play fighting as juveniles. Researchers have suggested this isn’t a defect but an adaptation. In an environment where the mother’s low-contact behavior signals potential danger or scarcity, a more defensive, vigilant temperament may actually help the offspring survive.
The truly striking finding is how specific this effect is. Even within the same litter, individual pups that received more licking from their mother had higher levels of stress-hormone receptors in the hippocampus as adults compared to their siblings who received less. The frequency of licking directed at each individual pup predicted that pup’s brain chemistry in adulthood.
Can the Effects Be Reversed?
One of the more hopeful findings from this research is that the epigenetic changes from low licking aren’t necessarily permanent. When rats raised by low-licking mothers were placed in enriched environments during adolescence (more space, more objects to explore, more social contact), at least some of the neurological effects of their early experience reversed. The brain retained enough flexibility to partially overwrite its initial programming when the environment changed.
Cross-fostering experiments confirmed that the effect comes from the licking itself, not from genetics. When pups born to low-licking mothers were placed with high-licking foster mothers, they developed the calmer stress profile of their foster mother’s biological offspring. The behavior, not the bloodline, shaped the brain.
Why It Varies Across Species
Not all animals lick their young with the same intensity or purpose. Cats and dogs lick extensively because their newborns are born blind, deaf, and completely dependent. Horses and cows lick their young but also nudge them to stand, since a foal or calf that can’t walk within an hour is in serious danger. Birds, of course, don’t lick at all but achieve similar bonding and thermoregulation through brooding and preening.
Among primates, licking is largely replaced by holding, carrying, and skin-to-skin contact, but the underlying biology is the same. Physical touch triggers oxytocin release, strengthens the parent-infant bond, and influences the developing nervous system. The tongue is just one tool for delivering what every mammalian newborn needs: sustained, warm, physical contact from a caregiver whose brain is chemically primed to provide it.