Human-made objects (artifacts) often provide rich social
information about the people who created them. We explore
how people reason about others from the objects they create,
characterizing inferences about when social transmission of
ideas (copying) has occurred. We test whether judgments are
driven by perceptual heuristics, or structured explanation-
based reasoning. We develop a Bayesian model of
explanation-based inference from artifacts and a simpler
model of perceptual heuristics, and ask which better predicts
people’s judgments. Our artifact-building task involved two
characters who built toy train tracks. Participants viewed pairs
of tracks, and judged whether copying had occurred. Our
explanation-based model accurately predicted on a trial-by-
trial basis when participants inferred copying; the perceptual
heuristics model was significantly less accurate. Efficient
design ‘explained away’ similarity, making similarity weaker
evidence of copying for efficient tracks. Overall, data show
that like intuitive archeologists, people make rich
explanation-based inferences about others from the objects
they create.