It is far too common to hear about puppies being adopted at an early age, even barely more than a month after birth. Unless they are puppies abandoned by their mother or by unscrupulous people, it is strongly inadvisable to separate such young animals from maternal care, for a long series of reasons. Here are the possible behavioral consequences.
What Happens During the First Two Months of Life
The puppy’s behavioral development begins even before birth, while it is still in the mother’s womb, and progresses and becomes stronger during the first months of life. The mother guides the puppy toward healthy behavioral development, also teaching it the basic rules of relationships with other animals.
It is no coincidence that puppies are born blind and deaf, with a very limited sense of smell and poorly developed neurological abilities. This mechanism is typical of predators, as is also the case with cats, because it ensures that the mother’s young can remain still in the same place while she is away.
All the experiences a puppy collects during the period required for its senses to develop fully will profoundly influence the animal’s character and behavior as an adult.
In fact, puppies seem to begin “recording” these experiences even before birth. During fetal life, they would be able to perceive the relaxing sensation of the caresses the owner gives the mother. In addition, according to some studies, the mother’s diet during pregnancy could influence the fetus’s future food preferences.
From birth until 10–15 days of age, this is known as the neonatal period. During this phase, the puppy is still blind, deaf, and barely sensitive to external events. The only fully developed sense is touch, so the puppy is especially sensitive to its mother’s care and contact with the mammary glands, but it nevertheless spends most of its time drowsy.
During this period, the hind limbs begin to develop, so we may start to notice these little creatures moving in a comical, swaying manner to reach their mother’s belly. 
During the neonatal phase, it is essential for the mother to care for the puppies by feeding, cleaning, and protecting them. If this does not happen, the puppy will very likely grow up to be insecure and fearful, having lacked maternal reassurance.
Once its eyes open, the puppy enters a transition period, which will not end until it is at least 4 weeks old. During this period, exploration begins, as the puppy devotes itself to discovering its surroundings and everything around it. In particular, contact with other animals and people is essential. Indeed, the animals most intimidated by humans or other dogs are precisely those that have not had the opportunity to meet, play with, and be handled by people and their own kind.
The socialization period follows, during which the puppy is attracted to, but at the same time intimidated by, all new situations. It becomes active, lively, sociable, and open to every discovery. During this phase it is more sensitive to reprimands and maternal instruction, and therefore also begins to understand the meaning of hierarchies.
Everything presented to the puppy during the socialization period will appear harmless to it for the rest of its life. It is therefore important for the puppy to have the opportunity to meet people, children, other domestic animals, and all the situations that might normally frighten dogs, such as noises inside or outside the home.
What Are the Consequences of Early Adoption
A puppy adopted during this period will have a very malleable character, and will therefore accept all the rules imposed by its owner fairly easily. To achieve this, however, it is important to know precisely what lessons to offer and, above all, how to offer them. A puppy in the socialization phase that is poorly or improperly trained by its owner will become a confused or insecure dog, unable to behave appropriately.
The direct consequences of these character traits inevitably translate into severe distress that the dog will feel in every “new” situation. For example, if the puppy has never seen a cat, it will very likely react at the first encounter by trying to attack it or, conversely, by running away as fast as it can.
One problem owners often have to deal with is the habit of biting objects, clothing, hands, and feet. Serial chewers can be recognized at any age, and this behavior is extremely difficult to eliminate. The cause is primarily the mother’s failure to teach the puppy to understand bite inhibition. A puppy separated too early from its maternal litter will always tend to bite, sometimes harder than appropriate, turning a simple pastime into a danger to our safety. This happens because the mother reprimands the puppy whenever, during play, it tends to bite its siblings too hard.
Another fairly complex aspect is attachment. Until 2 months of age, the puppy is dependent on its mother for everything and feels a very strong attachment, also due to the maternal body’s production of pheromones capable of stimulating the mother–offspring bond.
A puppy taken away from its own kind too early will inevitably suffer at first, and then become excessively attached to its owner. This is how overprotective, clingy dogs form—dogs that become agitated at the mere sight of their owner putting on a coat. This does not mean that a dog adopted after 2 months of age will not bond with us, but it will do so in a more mature and balanced way.
Let us therefore try to resist the idea of adopting a puppy that is too young. Let us avoid giving in to our impatience, which could cause serious damage to the dog’s psychological and behavioral balance.