The origins of human knowledge are an enduring puzzle: what parts of what we know require learning, and what depends on intrinsic structure? Although the nature-nurture debate has been a central question for millennia and has inspired much contemporary research in psychology and neuroscience, it remains unknown whether people share intuitive, prescientific theories about the answer. Here we report that people ( N = 1,188) explain fundamental perceptual and cognitive abilities by appeal to learning and instruction, rather than genes or innateness, even for abilities documented in the first days of life. U.S. adults, adults from a culture with a belief in reincarnation, children, and professional scientists—including psychologists and neuroscientists, all believed these basic abilities emerge significantly later than they actually do, and ascribed them to nurture over nature. These findings implicate a widespread intuitive empiricist theory about the human mind, present from early in life.

Many important questions about children’s early abilities and learning mechanisms remain unanswered not because of their inherent scientific difficulty but because of practical challenges: recruiting an adequate number of children, reaching special populations, or scheduling repeated sessions. Additionally, small participant pools create barriers to replication while differing laboratory environments make it difficult to share protocols with precision, limiting the reproducibility of developmental research. Here we introduce a new platform, “Lookit,” that addresses these constraints by allowing families to participate in behavioral studies online via webcam. We show that this platform can be used to test infants (11–18 months), toddlers (24–36 months), and preschoolers (36–60 months) and reliably code looking time, preferential looking, and verbal responses, respectively; empirical results of these studies are presented in Scott, Chu, and Schulz ( 2017 ). In contrast to most laboratory-based studies, participants were roughly representative of the American population with regards to income, race, and parental education. We discuss broad technical and methodological aspects of the platform, its strengths and limitations, recommendations for researchers interested in conducting developmental studies online, and issues that remain before online testing can fulfill its promise.

To help address the participant bottleneck in developmental research, we developed a new platform called “Lookit,” introduced in an accompanying article (Scott & Schulz, 2017 ), that allows families to participate in behavioral studies online via webcam. To evaluate the viability of the platform, we administered online versions of three previously published studies involving different age groups, methods, and research questions: an infant ( M = 14.0 months, N = 49) study of novel event probabilities using violation of expectation, a study of two-year-olds’ ( M = 29.2 months, N = 67) syntactic bootstrapping using preferential looking, and a study of preschoolers’ ( M = 48.6 months, N = 148) sensitivity to the accuracy of informants using verbal responses. Our goal was to evaluate the overall feasibility of moving developmental methods online, including our ability to host the research protocols, securely collect data, and reliably code the dependent measures, and parents’ ability to self-administer the studies. Due to procedural differences, these experiments should be regarded as user case studies rather than true replications. Encouragingly, however, all studies with all age groups suggested the feasibility of collecting developmental data online and the results of two of three studies were directly comparable to laboratory results.

From English to Hungarian to Mokilese, speakers exhibit strong ordering preferences in multi-adjective strings: “the big blue box” sounds far more natural than “the blue big box.” We show that an adjective’s distance from the modified noun is predicted not by a rigid syntax, but by the adjective’s meaning: less subjective adjectives occur closer to the nouns they modify. This finding provides an example of a broad linguistic universal—adjective ordering preferences—emerging from general properties of cognition.

Young children make sophisticated social and normative inferences based on proportional reasoning. We explored the possibility that proportional cues also help children learn from and about their own generosity. Across two experiments, 3- to 4-year-olds had the opportunity to give either 1 of 4, 1 of 3, 1 of 2, or 1 of 1 of their resources to an individual in need. We then measured children’s subsequent prosociality by looking at sharing behavior with a new individual. The more proportionally generous the initial action, the less likely children were to share selfishly in the second phase. Our results suggest that children make sense of their own actions using proportional cues and that giving children experience with difficult, prosocial actions increases the likelihood of their recurrence.

We introduce a novel method capable of dissecting the succession of processing stages underlying mental arithmetic, thus revealing how two numbers are transformed into a third. We asked adults to point to the result of single-digit additions and subtractions on a number line, while their finger trajectory was constantly monitored. We found that the two operands are processed serially: the finger first points toward the larger operand, then slowly veers toward the correct result. This slow deviation unfolds proportionally to the size of the smaller operand, in both additions and subtractions. We also observed a transient operator effect: a plus sign attracted the finger to the right and a minus sign to the left and a transient activation of the absolute value of the subtrahend. These findings support a model whereby addition and subtraction are computed by a stepwise displacement on the mental number line, starting with the larger number and incrementally adding or subtracting the smaller number.