What We Assume Matters: Part 1 of 5 on the Foundations of Behavior Analysis
Before we ever take data, run a session, or write a behavior plan, we’ve already made a decision. We’ve chosen to approach human behavior as scientists. And that decision—whether we name it or not—comes with a set of philosophical assumptions.
In behavior analysis, these assumptions are not decorative. They shape everything we do. They influence how we see the world, how we define problems, and what kinds of solutions we even believe are possible.
Over the next five blog posts, we’ll explore five core assumptions that give behavior analysis its scientific backbone:
- Selectionism
- Determinism
- Empiricism
- Parsimony
- Philosophic Doubt
Today, we begin with Selectionism, the idea that all behavior—like all life—is shaped by selection.
What Is Selectionism?
At its core, selectionism means that behavior doesn’t appear out of nowhere. It emerges and changes over time because of consequences. Those consequences may play out over millions of years, or over the course of a Tuesday afternoon.
Behavior changes in two main ways:
- Phylogenetically – across generations of a species
- Ontogenetically – across the lifespan of an individual
We evolved to be the way we are. And we learn to be the way we are.
Both matter.
Phylogeny: Our Evolutionary Backstory
Some patterns of behavior are deeply rooted in our species’ evolutionary history. You don’t teach an infant to cry when they’re hungry—it’s already in the repertoire. You don’t train someone to flinch at a sudden loud sound. These responses have survival value, and the capacity for them has been selected over thousands of generations.
For example, the human tendency to walk upright didn’t come from a therapist’s reinforcement schedule. It emerged as our ancestors adapted to their environment. The bipedal gait that’s now “natural” to most people was once a competitive advantage that made certain traits more likely to be passed down.
We inherit those adaptations whether we think about them or not.
Ontogeny: The Personal History That Shapes Us
Now zoom in.
At the level of one individual, selection still operates—but faster. We’re shaped not by generations, but by consequences in real time.
Take the example of a seasoned ultramarathoner. No one is born with the capacity to run 100 miles without stopping. That ability is shaped over years of training. Environmental consequences—internal and external—select for certain habits: discipline, pacing, pain tolerance, hydration strategies. The person becomes, over time, someone who can do something extraordinary.
Ontogeny reminds us that people aren’t fixed. They change. And behavior analysts are in the business of supporting that change.
Why This Matters in Our Work
Selectionism isn’t just a biological or academic concept—it’s a mindset. When we accept that behavior is shaped over time by interactions with the environment, it changes how we see our clients. It brings curiosity. Compassion. Precision.
Instead of asking, “What’s wrong with this person?” we ask, “What’s being reinforced here? What’s the learning history? What adaptations are we seeing?”
This doesn’t mean we reduce people to biology or ignore values or relationships. Quite the opposite. Selectionism invites us to look deeper. It reminds us that behavior is lawful, but also complex—and always embedded in a context.
When we honor that complexity, we move beyond isolated behavior events and start seeing the bigger picture: how lives are shaped, how systems reinforce or suppress certain patterns, and how meaningful change is possible.
Coming Up Next: Determinism
In the next post, we’ll explore Determinism—the idea that behavior is not random, and that things happen for a reason. Not a moral reason, but a functional one. We’ll talk about what it means to commit to finding those reasons, even when the path is murky.
Until then, here’s a question to reflect on:
What behaviors—your own or others’—make more sense when you think about them as shaped by selection?
Let’s keep asking good questions. Let’s stay rooted in the science.
The Learning Behavior Analysis Team