About

About Development grew out of an upper-level Psychology course that I’ve taught at Temple University (Philadelphia, USA) for the last decade or so. In teaching the course over the years, I became increasingly aware that when presenting some aspect of development – for instance, brain development – it is easy to focus on a mechanistic, what-happens-when account. Students are used to this, and perhaps expect it, and it still can lead to learning and an interesting semester. But behind all the details are questions that are very often left unexamined in psychology (and neuroscience) curricula.

We know a great deal about what happens as organisms develop. But explaining how those changes occur raises further questions. How does development result in an organized living being when the finished organism is not already present at the beginning? How can development be so reliable while also producing differences among individuals? In grappling with these questions, I also came to see that in psychology, we are not tracking findings in developmental biology and evolutionary theory that would help us understand development in a more coherent way.

We often explain the reliability of development by calling on some combination of maturation, genetics, and evolution. And differences between individuals are chalked up to particular genotypes interacting with particular environments. But if we look at how organisms actually develop, this framework explains much less than it seems to. The resource is an attempt to outline a different approach that has been put forward in various ways for a number of decades but that still remains in the background in psychology.

The readings make an argument, but they do not offer a method or a set of recommendations. What they try to change are the questions a reader brings to development: what a given explanation takes for granted, and how much of the history behind it needs to be followed. What to do with those questions in research, teaching, or practice is left to the reader, and I would be glad to hear what people make of them.

How the Readings Were Made

As part of the COVID-related switch to online instruction in early 2020, I moved away from a lecture format for my course on development, and I began to write up what I had in PowerPoint slides into a set of course readings. Over time, I began to think the material could be useful beyond my own classroom. There are many good textbooks on developmental psychology and neuroscience, but relatively few that approach development through the questions I wanted to ask.

My goal became to bring a set of readings together into a freely available educational resource that would offer a different way into thinking about development. As that goal has taken shape, I remain grateful to the students who have taken the course over the years for their feedback and questions. I have also benefitted from extended discussions with Troy Houser, Staci Weiss, Will Gyre Jaeger, and Summer Dib. The development of the resource was partially supported by an award from the Textbook Affordability Project of Temple University Libraries.

I originally used Microsoft Sway to house the readings, but as the resource grew, in 2023 I moved all the material into Google Docs, where I continued to develop and revise the readings, and I created a Google Site that housed the embedded documents. From 2023 to 2026 I would periodically revise the documents as a side project. Then in 2026 I finally figured out how to publish to GitHub Pages via Quarto, providing an opportunity to have the readings exist online in a more readable and professional format.

Unlike my journal articles, the readings have not been peer reviewed, although much of the argument they make was worked out in articles that were, particularly “Towards a Biologically Coherent Account of the Brain and How It Develops” (Human Development, 2024) and “Psychology in 2125” (Perspectives on Psychological Science, in press). The readings also describe a great deal of research by other people, from embryology to cortical development, and my summaries of that work have not been checked by anyone working in those areas. If you find something that is wrong, or that misrepresents a body of work, I would like to hear about it at pjm@temple.edu. Corrections will go into later versions, which are listed in the version history.

It has never been entirely clear to me who this resource is for. It began with a particular group of students, but as it grew beyond the course, its audience became less well defined. I have kept working on it because I enjoy working through these ideas, and I think they are important. Having the readings freely available is a way of sharing that ongoing effort. A companion resource, Enacting Life, goes further into embodiment, what makes living things different from machines, and different perspectives on knowledge and understanding. For more details on the wider context of this line of inquiry, and why I think it matters, see the background and commentary on my article “Psychology in 2125” at peterjmarshall.com.

A Note on AI Use

During summer and fall 2026, I used Claude and ChatGPT in revising and reorganizing these readings for publication. Most of the material had developed over the previous few years as I taught an upper-level course on development and neuroscience, but the readings varied in their organization and the connections between them were not always clear. The AI tools helped me compare explanations I had written at different times and see where they repeated or contradicted each other. Sometimes they suggested connections or distinctions I had not previously made, which I could consider, question, or reject. Although the original drafts were mine, the final version of the resource was the result of a lot of back and forth with these tools.

I think the assistance from AI tools improved the resource, and more generally these tools offer a real opportunity to make teaching materials clearer. But repeated revision toward clarity and consistency sometimes makes prose too smooth and can remove the particular way that I would otherwise express things. I am still working out what is gained and what might be lost, when AI participates in the writing process.

I remain conflicted about using these tools, even as I came to rely on them in finishing this resource. They depend on the intellectual work of many people, much of it used without their permission or recognition, and their development is driven by commercial interests and consumes substantial resources. The benefits I have seen for this resource do not settle those questions, and I am taking them up in a separate essay. I take responsibility for what appears here, while recognizing that the process of producing it involved more than my own unaided writing.