A defining feature of human culture is that knowledge and technology continually improve over time. Such cumulative cultural evolution (CCE) probably depends far more heavily on how reliably information is preserved than on how efficiently it is refined. Therefore, one possible reason that CCE appears diminished or absent in other species is that it requires accurate but specialized forms of social learning at which humans are uniquely adept. Here, we develop a Bayesian model to contrast the evolution of high-fidelity social learning, which supports CCE, against low-fidelity social learning, which does not. We find that high-fidelity transmission evolves when (1) social and (2) individual learning are inexpensive, (3) traits are complex, (4) individual learning is abundant, (5) adaptive problems are difficult and (6) behaviour is flexible. Low-fidelity transmission differs in many respects. It not only evolves when (2) individual learning is costly and (4) infrequent but also proves more robust when (3) traits are simple and (5) adaptive problems are easy. If conditions favouring the evolution of high-fidelity transmission are stricter (3 and 5) or harder to meet (2 and 4), this could explain why social learning is common, but CCE is rare.

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Surprisingly little is known about how social groups influence social learning. Although several studies have shown that people prefer to copy in-group members, these studies have failed to resolve whether group membership genuinely affects who is copied or whether group membership merely correlates with other known factors, such as similarity and familiarity. Using the minimal-group paradigm, we disentangled these effects in an online social-learning game. In a sample of 540 adults, we found a robust in-group-copying bias that (a) was bolstered by a preference for observing in-group members; (b) overrode perceived reliability, warmth, and competence; (c) grew stronger when social information was scarce; and (d) even caused cultural divergence between intermixed groups. These results suggest that people genuinely employ a copy-the-in-group social-learning strategy, which could help explain how inefficient behaviors spread through social learning and how humans maintain the cultural diversity needed for cumulative cultural evolution.

Timbre perception and auditory grouping principles can provide a theoretical basis for aspects of orchestration. In Experiment 1, 36 excerpts contained two streams and 12 contained one stream as determined by music analysts. Streams—the perceptual connecting of successive events—comprised either single instruments or blended combinations of instruments from the same or different families. Musicians and nonmusicians rated the degree of segregation perceived in the excerpts. Heterogeneous instrument combinations between streams yielded greater segregation than did homogeneous ones. Experiment 2 presented the individual streams from each two-stream excerpt. Blend ratings on isolated individual streams from the two-stream excerpts did not predict global segregation between streams. In Experiment 3, Experiment 1 excerpts were reorchestrated with only string instruments to determine the relative contribution of timbre to segregation beyond other musical cues. Decreasing timbral differences reduced segregation ratings. Acoustic and score-based descriptors were extracted from the recordings and scores, respectively, to statistically quantify the factors involved in these effects. Instrument family, part crossing, consonance, spectral factors related to timbre, and onset synchrony all played a role, providing evidence of how timbral differences enhance segregation in orchestral music.

There is a general consensus among archaeologists that replacement of Neanderthals by anatomically modern humans in Europe occurred around 40K to 35K YBP. However, the causal mechanism for this replacement continues to be debated. Searching for specific fitness advantages in the archaeological record has proven difficult, as these may be obscured, absent, or subject to interpretation. Proposed models have therefore featured either fitness advantages in favor of anatomically modern humans, or invoked neutral drift under various preconditions. To bridge this gap, we rigorously compare the systemlevel properties of fitness-and drift-based explanations of Neanderthal replacement. Our stochastic simulations and analytical predictions show that, although both fitness and drift can produce fixation, they present important differences in 1) required initial conditions, 2) reliability, 3) time to replacement, and 4) path to replacement (population histories). These results present useful opportunities for comparison with archaeological and genetic data. We find far greater agreement between the available empirical evidence and the system-level properties of replacement by differential fitness, rather than by neutral drift. IntroductionExplaining the disappearance of Neanderthals from the archaeological record during the Upper Palaeolithic is a longstanding and ongoing debate involving anthropologists, archaeologists, biologists, and geneticists. Homo neanderthalensis, commonly known as Neanderthals, were an archaic branch of the genus Homo. They appeared first in Europe around 400K YBP, evolving out of ancestral variants of Homo erectus or Homo heidelbergensis, who had previously spread into Europe from Africa by 800K YBP. After being the sole hominin occupants of Europe for some 350K years, Neanderthals disappeared from the archaeological record at roughly the same time that anatomically modern humans (hereafter Moderns) spread from Africa through Europe via the Levant around 50K to 35K YBP 1-3 .Evidence for the replacement of Neanderthals by Moderns is morphological, archaeological, and genetic. Neanderthal skeletal remains feature unique morphological characteristics beyond the variation present in Moderns 4,5 , and these traits disappear from the fossil record over time. Likewise, associated archaeological cultures, such as the Mousterian, are replaced by those associated with Moderns 6 . Genetic research in the last decade has revealed a Neanderthal DNA contribution of 1 to 4% to contemporary non-African populations, leading most experts to agree that some interbreeding did occur 7-10 ,