Proximate vs Ultimate Explanation
Separate why a behaviour feels compelling from why it evolved, and the naturalistic fallacy dissolves
- Difficulty
- Easy
- Time to result
- ~days to results
- Steps
- 4
- Confidence
- 72%
Every behaviour has two kinds of explanation. The proximate explanation is the immediate, felt cause: you eat because food tastes good, you have sex because it feels good, you grieve because you love the person. The ultimate explanation is the evolutionary function that built that drive: eating keeps you alive, sex produces offspring, grief tracks reproductive value. The mental model is to hold the two apart. The ultimate cause is never a conscious motive running in your head — Darwin was not thinking about reproductive value when his daughter died. Keeping the levels separate defuses two errors at once: the objection that 'sex can't be about babies because people don't want babies' (a confusion of levels), and the naturalistic fallacy that an evolved behaviour is thereby justified. Analysis is not justification.
Origin
A standard distinction in evolutionary biology (Tinbergen's levels of explanation) that Stewart-Williams deploys throughout the conversation to defuse common misreadings of evolutionary psychology.
Core principles
- 01The felt reason for a behaviour is not the same as its evolutionary function.
- 02Evolutionary explanations describe why we have a drive, not a motive we consciously hold.
- 03All behaviour has causes, whether evolutionary, cultural, or both — that never removes responsibility.
- 04Explaining a behaviour is not the same as excusing it: analysis is not justification.
- 05An evolved gut reaction can fire even when its original function no longer applies.
How to run it
- 1
Name the behaviour and its felt motive
Pick the behaviour and state the proximate cause — the reason it feels compelling in the moment. You eat because food tastes good; you have sex because it feels good; you grieve because you love the person.
Pro tip The proximate cause is what you would actually report if asked why you did it.
- 2
State the ultimate, evolutionary function
Now ask what evolutionary function shaped that drive. Eating keeps you alive; sex produces offspring; grief that intensifies with a child's reproductive value tracked ancestral fitness.
Pro tip Ask 'what would this drive have accomplished for my ancestors?' rather than 'what do I want right now?'
- 3
Keep the two levels apart
Do not collapse the ultimate cause into a conscious motive. Darwin grieved his 13-year-old most intensely without any thought of reproductive value; the algorithm ran underneath, not in his mind.
Pro tip If your explanation implies people are secretly calculating fitness, you have collapsed the levels — back up.
Watch out Most bad internet rebuttals to evolutionary psychology are exactly this collapse ('so you're saying it's just about babies').
- 4
Run the naturalistic-fallacy check
Having an evolutionary explanation for a behaviour never makes it good, permissible, or excused. A sociocultural explanation would not excuse it either, so the evolutionary one does not.
Pro tip Hold the phrase 'analysis is not justification' — explaining bad behaviour leaves it just as bad.
In the wild
A friend's father had a one-night stand 32 years ago; three decades later a half-sibling surfaces via a DNA test. The old jealousy and betrayal reaction can fire hard even though, evolutionarily, none of the original stakes remain — the dependent child is grown, no resources are threatened. Using proximate vs ultimate, Stewart-Williams notes the gut reaction (proximate) evolved to serve an ancestral function (ultimate) but does not check whether that function still applies. The feeling kicks in regardless. Separating the levels explains why the reaction is real and intense without implying the person is consciously computing lost fitness.
→ A clean account of why an evolved emotional reaction can misfire in a modern context, without collapsing into 'you're secretly thinking about genes'.
Common mistakes
Treating the ultimate cause as a conscious motive
Assuming people literally think about reproductive value or gene propagation misreads the model. Evolutionary explanations describe why the drive exists, not what the person is thinking.
Sliding from explanation to excuse
Believing that an evolutionary account of cheating, violence, or coercion justifies it is the naturalistic fallacy. Explaining a behaviour leaves its moral status untouched — analysis is not justification.
Is it for you?
Best for
Anyone trying to understand human motivation, or debating evolutionary claims, who keeps hitting the 'so you're saying it's just about babies' confusion.
Not ideal for
Situations that need a moral verdict — this model explains causes, it does not deliver ethical judgments.
From the transcript
“You eat food because it tastes good. But the reason for eating food is to keep you alive.”
“the evolutionary explanations those are not motivations. Those are just explanations for why we have the proximate psychological drives that we do”
“analysis is not justification”
From the episode
The Uncomfortable Science Of Sex Differences - Steve Stewart-Williams - #1120
Williams