|5 months old and venturing off on her own.|
In all this reading, I discovered a sneaky truth: there are no hard-and-fast timelines, nor even agreement on what each stage is called. The first part wasn't really a surprise, but I was a bit taken aback by the fact that there are so many ways to break down a puppy's development. I'm going to try to synthesize this material into something cohesive, but you should keep in mind that these periods can overlap, and that the breed of the dog will influence the timelines.
Neonatal Period, birth to 14 days
The neonatal period is rather boring, truth be told. In this stage, a puppy's eyes are closed and he is functionally deaf. He is completely dependent on his mother, and researchers have found little to no classical conditioning happening at this stage (at least, not in a way they could use). The puppy's task at this time is to develop some basic mobility and sensory awareness.
Transitional Period, 14 to 21 days
The transitional period begins when the puppy's eyes open and ends when he startles at noises. This usually takes place between 2 and 3 weeks. The pup's eyes will be a hazy or cloudy blue color, and will remain that way until 6 to 8 weeks. The teeth begin to form this point, and the sensory capabilities continue to develop.
Socialization Period, 3 weeks to ?? weeks
During this period of time, which most sources agree starts around 3 weeks, the puppy's brain develops rapidly. Although a puppy is born with basically all the brain cells he will ever have, the brain volume increases greatly due to the synaptic connections that are being physically formed. The Coppingers did brain scans and found that when a puppy is born, his brain volume is 8 cubic centimeters. By 2 months, it's 50 cubic cm, 80 cubic cm by 4 months, and 100 cubic cm at 12 months, which tends to be its final amount.
The connections that are being formed are due to socialization. This is where the puppy basically learns safe vs. not safe. If he encounters novel people/dogs/animals/surfaces/objects/sounds/etc. and has a good experience, that thing becomes classified as safe. If he encounters something and has a bad experience, that thing becomes not safe. If he doesn't encounter a certain thing at all, it will default to the not safe category. This is where behavioral problems like fear or aggression can come from.
The socialization window ends anywhere from 10 to 16 weeks. Dehasse says that studies have shown that between 3 to 5 weeks, a puppy will investigate just about anything without much hesitancy. At 7 to 9 weeks, the puppy needs more time to overcome his uncertainty (Dehasse uses the the word “fear”) and investigate a novel person. At 12 weeks, the puppy can overcome his fear, but only with “active manipulation” from the person. At 14 weeks, Dehasse says that socialization to people is nearly impossible if the dog hasn't already experienced them.
The Coppingers assert that by 16 weeks, a dog's personality is set for life. If he's timid at 16 weeks, he'll be timid at 3 years. They acknowledge that training and behavior modification can change the dog's personality, but are quick to say that the dog will have a social “accent” for the rest of his life. I really, really like that phrase, because it's a great way of describing how a dog can change yet still have lingering effects from the past.
Other things that happen during this stage:
At 3 weeks of age, the puppies begin to play with one another. From now until 7 weeks, they are developing bite inhibition. This is why it is so important that puppies stay with their litter for at least this long.
Mother dogs tend to initiate weaning at about 5 weeks. She does this by growling or snapping at her pups, especially when their sharp little puppy teeth hurt her teats. In response, the pups will roll over in deference. A puppy who is force weaned by being separated from his mom tends to show a reduction in appeasement behaviors; he has literally not learned how to do them. This can create issues in social hierarchies down the road.
House training happens during this stage as well. In the neonatal period, Momma Dog stimulates elimination. Around 2 to 3 weeks, elimination becomes spontaneous on the part of the puppy, and very soon after, the puppy will leave the bedding area to eliminate. By 8 weeks, the puppy will have developed substrate preferences for elimination. This is why it is so hard to house train a mill or pet store puppy; he has literally learned to pee where ever he is at the moment.
Fear Periods Multiple, but first one 7 to 12 weeks
This is probably where the biggest variation between puppies occurs. Although puppies will go through several fear periods- defined as a time when the puppy is especially sensitive to bad experiences- they vary in timing and number. Dehasse argues that the first fear period begins when the socialization period ends; around 12 weeks. The Coppingers, on the other hand, suggest that the first fear period starts around 7 weeks.
The owner's job during this time, whenever it happens, is to prevent or minimize bad experiences as much as possible. Bad experiences tend to be traumatic at this time and has a lifelong impact on behavior. There is at least one more fear period (and sometimes more than one) between 6 and 14 months, which roughly correlates with puberty.
Hierarchy and Status Development, 3 to 4 months
Bennett and Briggs were the only ones to label this as a separate developmental period, although Dehasse did allude to it. During this time, dogs start to figure out who they are in relation to other dogs. They also begin teething during this time as their incisors come in.
Flight Instinct or Exploration Period, 4 to 8 months
Puppy develops some independence during this period. He changes from the sweet shadow that follows you everywhere to no longer needing the immediate protection of his owner. This manifests itself as a desire to explore territory, and he will venture further and further away. This is the period where dogs begin to “blow off” their recall cues and find being chased a grand game!
Puberty, 6 to 12 months
During this time, pups begin to figure out all things sexual. An unspayed female will go into heat for the first time around now. Dogs will also begin to show wariness of the unknown. Dehasse says this isn't so much a behavioral fear as it is a cognitive process.
Social Maturity, 1 to 3 years
Social maturity very much depends on the breed, with smaller dogs tending to enter social maturity before bigger dogs. During this time, we see the effects of the earlier periods, and especially the results of our socialization efforts (or lack thereof) and experiences during the fear periods. This means it's when reactivity or aggression tends to rear its ugly head.