Weaning is the process of gradually introducing a mammal infant to what will be its adult diet and withdrawing the supply of its mother's milk.

The process takes place only in mammals, as only mammals produce milk. The infant is considered to be fully weaned once it no longer receives any breast milk (or bottled substitute).

Weaning in human infants[link]

How and when to wean a human infant is a subject of much controversy. The American Academy of Pediatrics recommends feeding a baby only breast milk for the first 6 months of its life, and continuing breastfeeding until the child is at least one year old and for as long after that as the mother and child both wish to continue.^[1] However many mothers find breastfeeding challenging, especially in modern times when many mothers have to return to work relatively soon after the birth of their child. Weaning a baby to formula within the first two months of life is not uncommon in the United States. At this age babies have no teeth and must rely exclusively on formula.

The American Academy of Pediatrics and the World Health Organization recommend waiting until 6 months to introduce baby food.^[1] However, many baby food companies market their "stage 1" foods to children between 4 and 6 months old with the precaution that the food is meant to be consumed in addition to breast milk or formula and is just for "practice". These practice foods are generally soft and runny. Examples include mashed fruit and vegetables. Certain foods are recommended to be avoided. The United Kingdom's NHS recommends withholding nuts, eggs and shellfish until a baby is six months old, in order to reduce allergic reactions.^[2] However, recommendations such as these have been called into question by research that suggests early exposure to potential allergens does not increase the likelihood of allergic reactions.^[3]

No matter what age baby food is introduced, it is generally a very messy affair, as young children do not have the coordination to eat "neatly". Coordination for using utensils properly and eating with dexterity takes years to develop. Many babies begin using utensils between 10 and 14 months, but most will not be able to feed themselves well until about 2 or 3 years of age.

Weaning conflict[link]

Weaning conflict occurs when the mother wishes to stop nursing but the infant wishes to continue.^[4] At this point, the mother tries to force the infant to cease nursing, while the infant attempts to force the mother to continue. From an evolutionary perspective, weaning conflict may be considered the result of the cost of continued nursing to the mother, perhaps in terms of reduced ability to raise future offspring, exceeding the benefits to the mother in terms of increased survival of the current infant.^[4] This can come about because future offspring will be equally related to the mother as the current infant, but will share less than 100% of the current infant's genes. So, from the perspective of the mother's evolutionary fitness, it makes sense for her to cease nursing the current infant as soon as the cost to future offspring exceeds the benefit to the current infant.^[4] But, assuming the current infant shares 50% of the future offsprings' genes, from the perspective of the infant's own evolutionary fitness, it makes sense for the infant to continue nursing until the cost to future offspring exceeds twice the benefit to itself (perhaps less, depending on the number of potential future offspring).^[4][5] Weaning conflict has been studied for a variety of mammal species, including primates and canines.^[6][7][8]

Age of weaning[link]

There is significant individual and cultural variation in time of weaning.

Scientifically, one can ask various questions; some of the most straightforwardly empirical include:

• At what age do children self-wean?
• At what age do various societies normatively choose to wean?
• In comparison with other animals, especially similar primates, by various measures.

As there are significant ranges and skew in these numbers (some infants are never nursed, or only nursed briefly, for instance), looking at the median (half-way mark) is more useful than looking at the average.^[9]

Considering biological measures of maturity, notably investigated by Kathy Dettwyler, yields a range of ages from 2 1/2 years to 7 years as the weaning age analogous to other primates – the "natural age of weaning".^[9] This depends on the measure, for example: weaning in non-human primates is often associated with eruption of permanent molars (humans: 5 1/2 to 6 years); comparing duration of nursing to length of pregnancy (gestation time) yields a factor of about 6 in chimpanzees and gorillas (humans: 6×9 months = 54 months = 4 1/2 years); body weight may be compared to birth weight (quadrupling of birth weight yields about 2 1/2 to 3 1/2 years for humans; 1/3 of adult weight yields 5 to 7 years for humans); and similarly for other measures.

The age at which children are normatively weaned can vary significantly between cultures, "from 6 months to 5 1/2 years".^{[citation needed]} There is often a cultural expectation in the United States that children be weaned early, and there have been scientific studies performed to validate this expectation.^{[citation needed]}

Other studies are possible, as in psychological factors. For example, Barbara Rogoff has noted, citing a 1953 study by Whiting & Child, that the most distressing time to wean a child is at 13-18 months. After this peak, weaning becomes progressively easier and less distressing for the child, with "older children frequently wean[ing] themselves."^[10]

Weaning in other mammals[link]

In science, mice are frequently used in laboratory experiments. When breeding laboratory mice in a controlled environment, the weaning is defined as the moment when the pups are transferred out of the mothers' cage. Weaning is recommended at 3 to 4 weeks after parturition ^[11].

For pet carnivores such as dogs or cats, there are special puppy or kitten foods commercially available. Alternatively, if the pet owner feeds the parent animals home-made pet food, the young can be fed the same foods chopped into small pieces.

See also[link]

• Breastfeeding
• Baby-led weaning
• Baby food
• Lactation
• Male lactation
• Prolactin

References[link]