Abstract
Every dog is different, has a different personality, has different reactions to the same stimulus. Even siblings from the same litter can differ.
However, despite the different personalities, we can identify certain similarities in the lives of most dogs and bitches that are associated with age and life's vicissitudes. Between birth (for some, already by insemination) and death, the development of the individual takes place (ontogeny).
With closer observation of multiple individuals, it is possible to delineate other milestones in ontogenetic development, developmental periods that all individuals go through, albeit each in their own way. The existence of several key developmental periods in dogs was first pointed out by Scott in 1958.
But I would say that the subject has not yet been elaborated as much as it needs to be. I have taken the liberty of elaborating it somewhat.
The basis for my reflections is my own observation, knowledge of developmental theories and knowledge of developmental psychology and cynological literature.