At this point I think that we have enough on the table to begin talking about the developmental process. We have mentioned stages and aspects and phases, and maybe it still feels like we haven't described anything, yet. We know that people are complicated, so it stands to reason that the developmental process, if it is to be in any way accurate, will be at least similarly complex. Generally, the way that complex problems are broken down is by isolating different aspects and dealing with them in isolation before then considering them in collaboration. Which is actually exactly what psychology has been doing for the last couple of decades! Great news. So, applying our First Law of Human Dynamics, we want to identify different parts of people that we think every person has.
First we can identify the body. We all have one. At least, as far as I am aware. When I run into a disembodied human I will update my perspectives. So we have a body, and that body goes through a series of changes that compound in a gradual process leading to a greater complexity, and an accompanying greater range of functionality. This is the foundation for a lot of the changes that happen in the other areas of development. To be clear, I am not suggesting that every psychological change is entirely determined by biological changes. There are definitely social, cultural, geographic, and general environmental factors that come into play. What I am saying is that some of these developmental changes are made possible by biological changes. The ability to walk depends on the post-natal growth of the inner ear allowing for balance. Puberty follows the advent of hormones and a bump in brain space. There are things that we can do that hasten or inhibit those biological changes, but those biological changes create new capabilities and functionalities. If I want to understand the process, I start with the biological, and then I understand different aspects in light of those biological parameters.
This is a good point to address what has been a frequent misunderstanding in the many conversations that lead to this project. DNA is awesome. We understand a lot about the mechanics of how we work in light of the recent work in genetics. I just submitted my 23andMe sample a few weeks ago. I'm excited to know about my genetic marker and predispositions, because I know exactly what they are: markers and predispositions. Here is the critical distinction: genes are not fate. A high-risk allele just indicates that your risk is higher. You then have a choice as to whether or not to modify your behavior to adjust for your higher risk. What appears to be the difference between genes and fate is human volition. We have a lot of influence acting upon us at all times, and usually by being aware of them we can more appropriately decide how to respond to them.
That is to say, we have been thinking about how people think and why they behave the way they do for a very long time, but we only recently began writing down predictions and testing them. This is when the rapid development of the field exploded and is another testament to the benefit of the scientific method, when used appropriately. This is what happens when you make a prediction, which you have been carefully cultivating over decades of painstaking research in collaboration with your colleagues, who have become some of your closest and only friends: all of those friends and colleagues spend the rest of their careers trying to prove you wrong. The history of psychological development is littered with dalliances and schisms, and would make for a terrific, if geektacular, soap opera. This theoretical cannibalism has a similar effect to the purification of gold, in that this trial by fire burns away the parts of the theories that don't work. This does not prove the theory. This is a common misconception. Science doesn't really prove anything. Good science disproves things. You could consider science as an ongoing voyage of discovery of all of the ways that we used to be wrong.
Hall, Freud, and Piaget wrote some predictions down and a whole bunch of people tried to prove them wrong, and managed to do so in some areas and failed to do so in others. This is how the subsequent fields of developmental psychology grew, out of trying to explain the things that Freud and Piaget did not explain. A large part of the language of this dialectic was informed by some concepts that Hall, Freud, and Piaget used, namely that children go through a process of becoming adults, early life events influence the trajectory or nature of this process, and that the process appears to go in a progression of steps, which they called stages. As a result, most of the theories proceed in stages, though this is mostly a tool to note particular events in the process in relation to each other chronologically.
Freud was singularly important to the general field of developmental theory, as the first person who really connected early life events to later life habits and dysfunctions. This seems like the kind of thing that can come across as being obvious, now, but that is because all of us got to grow up in a world where Freud had already demonstrated this reality. At the time, this was a revolutionary concept, and the rest of the field spilled out of it.