The Engine of Development: What Growth Requires Across All Neurologies

Every human being, regardless of neurology, is trying to do the same thing across the course of a life. They are trying to become more fully themselves. To understand who they are in relation to the world around them. To build trust, find autonomy, develop initiative, form an identity, achieve intimacy, contribute something, and arrive at the end of life with a sense that it meant something.

Erik Erikson mapped those destinations in the middle of the twentieth century, and his map remains one of the most durable frameworks in developmental psychology (Erikson, 1963, 1980). Trust. Autonomy. Initiative. Industry. Identity. Intimacy. Generativity. Integrity. These are not non-autistic destinations or autistic destinations. They are human destinations. The question this series is asking is not whether autistic and non-autistic people are headed somewhere different. They are headed to the same place. The question is what the journey looks like, and what each traveler needs in order to make it.

The Simplest True Thing About Growth

Beneath all of the theoretical language, beneath Piaget and Baumrind and Csikszentmihalyi and Erikson, there is one simple truth about human development that every framework is really describing in its own way.

Growth requires learning something new, and then applying it. And then learning something new again, and applying that. Over and over, across a lifetime.

That's it. That's the engine.

Everything else is a description of what that engine looks like from different angles, or what conditions allow it to run well, or what happens when those conditions are absent. But the engine itself is the same for every human being who has ever developed into more than they were before.

Jean Piaget called the two movements of this engine assimilation and accommodation (Piaget, 1952). When we encounter something new that fits our existing understanding of the world, we assimilate it: we take it in, we file it, we move on. When we encounter something that doesn't fit, we accommodate: we reorganize our understanding to make room for it. The mind is not a passive container. It is an active, adapting system, constantly adjusting itself to the world and the world to itself. Piaget described this process in children, but the SAGE Encyclopedia of Lifespan Human Development is clear on this point: assimilation and accommodation operate across the entire lifespan (Maynard, 2018). The engine doesn't stop at adolescence. It runs as long as we do.

Diana Baumrind described the same engine from the outside, through the lens of what environments do to support or impede it. She organized developmental environments along two dimensions: responsiveness and demandingness (Baumrind, 1991; Maccoby & Martin, 1983). Responsiveness is warmth, attunement, presence: the environment meeting the person where they are.

Demandingness is challenge, expectation, the requirement to reach: the environment asking something of the person that they have not yet fully mastered. Healthy development, Baumrind found, requires both in balance (Baumrind, 1991). An environment that is only responsive produces comfort without growth. An environment that is only demanding produces anxiety without the safety needed to take the risks that growth requires. The engine needs fuel from both directions.

Mihaly Csikszentmihalyi arrived at the same place from yet another angle. His decades of research into optimal human experience produced the concept of flow: a state of deep engagement that occurs when the challenge of a task and the ability of the person meeting it are roughly matched (Csikszentmihalyi, 1990). Too much challenge and the person is overwhelmed, anxious, unable to move forward. Too little challenge and the person is bored, stagnant, coasting on what they already know. The narrow channel between those two states, where the challenge is just slightly beyond current ability, is where optimal development occurs. Where the engine runs at its best.

Piaget, Baumrind, Csikszentmihalyi. Three different researchers, three different methodologies, three different vocabularies. The same engine.

What the Engine Needs to Run

Understanding the engine is one thing. Understanding what it needs in order to run is another, and this is where neurology enters the picture in a significant way.

The engine of development does not run in isolation. It runs in relationship. It runs in environment. Human beings do not develop by thinking in rooms alone. They develop through encounter: with other people, with challenges, with feedback from the world about who they are and how their actions land. Development is always, at its core, a relational process.

Robert Kegan, the Harvard developmental psychologist, made this the center of his life's work. His constructive-developmental theory proposes that human beings move through successive orders of mind across adulthood, each representing a qualitatively different way of making meaning, a deeper and more complex capacity to hold the self in relation to others and to the world (Kegan, 1982, 1994). But Kegan's most practically important insight may be his concept of the holding environment.

A holding environment, in Kegan's framework, is not simply a supportive space. It is something more precise: a context that simultaneously confirms a person where they are and challenges them toward where they are going. It holds on and lets go at the same time. It provides the safety that makes risk possible and the demand that makes safety insufficient. It attends, as Kegan put it, concurrently to the stage from which a person is transitioning and the stage toward which they are moving (Kegan, 1982).

This is Baumrind's responsiveness and demandingness expressed at the level of the whole developmental environment. And it describes, with precision, what every human being needs in order for their developmental engine to keep running across the lifespan.

The question, then, is not whether autistic and non-autistic people need holding environments. They do. Both do. The question is what those holding environments need to look like for each neurotype, and why the environments we have built so far have served one neurotype far better than the other.

Feedback Is the Fuel

There is one more element of the engine that must be named before the two developmental pathways can be understood clearly. It is the element that Csikszentmihalyi identified as essential to flow, and that Warlaumont and colleagues demonstrated empirically in the context of early development: feedback (Csikszentmihalyi, 1990; Warlaumont et al., 2014).

Csikszentmihalyi was explicit about this. Flow, and by extension optimal development, requires not only balanced challenge and ability. It requires immediate feedback on how one is doing (Csikszentmihalyi, 1990). Without feedback, the engine cannot calibrate. Without calibration, it cannot stay in the channel between overwhelm and stagnation. Without that channel, growth slows or stops.

Warlaumont and colleagues showed this operating at the earliest level of human development: infants whose vocalizations received immediate adult responses were significantly more likely to develop speech (Warlaumont et al., 2014). The feedback loop was not just encouraging. It was structurally necessary. It shaped the trajectory of development itself.

This is the point at which autistic and non-autistic development begin to diverge, not in destination, not in the underlying engine, but in the feedback mechanisms available to each neurotype, and in what those different feedback mechanisms mean for the shape of the developmental journey.

Both neurotypes are running the same engine. Both need holding environments. Both need the balance of challenge and ability, responsiveness and demandingness, assimilation and accommodation. Both are headed toward trust, identity, intimacy, generativity, integrity.

But the feedback mechanisms are different. And because the feedback mechanisms are different, the pathways look different. One moves in a spiral. One moves in a staircase.

Neither is the default. Neither is the variation. They are two equally valid, structurally distinct expressions of the same human drive toward growth.

That is where we turn next.

Next in this series: Two Paths Upward, MacMillan's Spiral Model of Non-Autistic Development™ and MacMillan's Staircase Model of Autistic Development™, introduced together, in full.

This post is part of an ongoing series on MacMillan's Spiral and Staircase Model™ of psychosocial development across neurologies:

Post 1. The Gap: Why Developmental Psychology has Never Fully Accounted for Autism
Post 2. The Engine of Development: What Growth Requires Across all Neurologies
Post 3. Two Paths Upward: MacMillan's Spiral and Staircase Models of Psychosocial Development
Post 4. The Holding Environment: What Development Actually Requires
Post 5. The Destination is the Same: Erikson's Full Arc Across Neurologies

References

Baumrind, D. (1991). The influence of parenting style on adolescent competence and substance use. The Journal of Early Adolescence, 11(1), 56–95. https://doi.org/10.1177/0272431691111004

Csikszentmihalyi, M. (1990). Flow: The psychology of optimal experience. Harper & Row.

Erikson, E. H. (1963). Childhood and society (2nd ed.). W. W. Norton.

Erikson, E. H. (1980). Identity and the life cycle. W. W. Norton.

Kegan, R. (1982). The evolving self: Problem and process in human development. Harvard University Press.

Kegan, R. (1994). In over our heads: The mental demands of modern life. Harvard University Press.

Maccoby, E. E., & Martin, J. A. (1983). Socialization in the context of the family: Parent-child interaction. In P. H. Mussen (Ed.) & E. M. Hetherington (Vol. Ed.), Handbook of child psychology: Vol. 4. Socialization, personality, and social development (4th ed., pp. 1–101). Wiley.

Maynard, A. E. (2018). Accommodation and assimilation. In M. H. Bornstein (Ed.), The SAGE encyclopedia of lifespan human development (Vol. 5, pp. 10–11). SAGE Publications. https://doi.org/10.4135/9781506307633.n11

Piaget, J. (1952). The origins of intelligence in children (M. Cook, Trans.). International Universities Press. https://doi.org/10.1037/11494-000

Warlaumont, A. S., Richards, J. A., Gilkerson, J., & Oller, D. K. (2014). A social feedback loop for speech development and its reduction in autism. Psychological Science, 25(7), 1314–1324. https://doi.org/10.1177/0956797614531023