Weaning

Weaning is the process of gradually introducing a mammal infant, either human or animal, 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
Solid food is gradually introduced to a baby's diet, alongside its previous diet of breast or formula milk, at around six months (though this varies slightly from child to child). Before this, a child's digestive system and kidneys are still developing and are not yet ready to deal with solid food.

Soft, runny food such as mashed fruit and vegetables or premasticated foods are introduced to babies in the early stages of weaning, as they do not have teeth and are unable to chew. Certain foods are recommended to be avoided, such as those containing nuts or high levels of gluten, salt, or sugar. The United Kingdom's NHS recommends withholding nuts, eggs and shellfish until a baby is six months old, in order to reduce allergic reactions. 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.

Weaning conflict
Weaning conflict occurs when the mother wishes to stop nursing but the infant wishes to continue. 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. 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. 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). Weaning conflict has been studied for a variety of mammal species, including primates and canines.

Cultural variations in age at time of weaning
The age at which children are normatively weaned can vary significantly between cultures, "from 6 months to 5 1/2 years". 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. However, as Barbara Rogoff has noted, citing a 1953 study by Whiting & Child, 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."

Weaning in other mammals
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.