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To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while nevertheless falling within the mammalian range. Additionally, female reproductive skew is higher in polygynous human populations than in polygynous nonhumans mammals on average. This patterning of skew can be attributed in part to the prevalence of monogamy in humans compared to the predominance of polygyny in nonhuman mammals, to the limited degree of polygyny in the human societies that practice it, and to the importance of unequally held rival resources to women's fitness. The muted reproductive inequality observed in humans appears to be linked to several unusual characteristics of our species-including high levels of cooperation among males, high dependence on unequally held rival resources, complementarities between maternal and paternal investment, as well as social and legal institutions that enforce monogamous norms.

This study sought to determine if a child’s inventory of denominal verbs (e.g., swing as a verb) at 42 and 54 months are predicted by their inventory of related nouns (e.g., swing as a noun) at 30 months and whether these relationships are different for late talking and typically developing children. Keywords consisting of denominal verbs and related nouns were extracted from 42 late talking and 44 typically developing children at 30, 42, and 54 months. Preliminary results revealed that related noun inventories at 30 months predict denominal verb inventories at 42 months. However, related noun inventories at 30 months do not predict denominal verb inventories at 54 months. These results suggest that differences in noun inventories are linked to denominal verb inventories regardless of language status, but only in an early window of development.

The intensifying pace of research based on cross-cultural studies in the social sciences necessitates a discussion of the unique challenges of multi-sited research. Given an increasing demand for social scientists to expand their data collection beyond WEIRD (Western, educated, industrialized, rich and democratic) populations, there is an urgent need for transdisciplinary conversations on the logistical, scientific and ethical considerations inherent to this type of scholarship. As a group of social scientists engaged in cross-cultural research in psychology and anthropology, we hope to guide prospective cross-cultural researchers through some of the complex scientific and ethical challenges involved in such work: (a) study site selection, (b) community involvement and (c) culturally appropriate research methods. We aim to shed light on some of the difficult ethical quandaries of this type of research. Our recommendation emphasizes a community-centred approach, in which the desires of the community regarding research approach and methodology, community involvement, results communication and distribution, and data sharing are held in the highest regard by the researchers. We argue that such considerations are central to scientific rigour and the foundation of the study of human behaviour.

Several of the central questions in language, social cognition,and developmental research focus on the roles of input, out-put, and interaction on learning and communication. While ithas become easy to collect long-form recordings, getting use-ful data out of them is a more daunting task. Across four mini-sessions, this tutorial aims to address pre- and post-data collec-tion concerns, and provide a hands-on introduction to manualand automated annotation techniques. Attendees will leave thistutorial with resources and concrete experience for collecting,annotating, and sharing/archiving naturalistic recordings, in-cluding specific open-science practices relevant for these data.

Child-directed speech (CDS) shows similar characteristics across many languages, but is known to vary across cultural anddemographic groups (Lieven, 1994). Is CDS consistently discriminable from adult-directed speech (ADS) despite thesedifferences? Perhaps: adults listening to scripted female CDS can discriminate ADS-vs-CDS in a language they dontspeak (Bryant et al., 2012). We build on this finding by asking North American English speakers to classify utterancesfrom the natural language input of 10 Tseltal Mayan children as ADS or CDS (n = 1836 utterances). Binomial mixed-effects regressions of accuracy show that listeners are more accurate on utterances from females (mFemale = .81, mMale =.67) and adults (mAdult = .82, mChild = .72), with a larger gender effect for child speakers (m: Girl-Boy = 0.31, Woman-Man = 0.09). This suggests that (a) ADS-CDS discrimination of natural speech in an unrelated, non-familiar language isreliable (mAll = 0.78) and also (b) modulated by speaker type.

With apologies, an incorrect author list was given in the article. An additional author, Chris von Rueden, (Jepson School of Leadership Studies, University of Richmond) also contributed to this work. Author Ryan Schacht's affiliation was out-of-date. His correct affiliation is: Department of Anthropology, East Carolina University.

Monogamy appears to have become the predominant human mating system with the emergence of highly unequal agricultural populations that replaced relatively egalitarian horticultural populations, challenging the conventional idea-based on the polygyny threshold model-that polygyny should be positively associated with wealth inequality. To address this polygyny paradox, we generalize the standard polygyny threshold model to a mutual mate choice model predicting the fraction of women married polygynously. We then demonstrate two conditions that are jointly sufficient to make monogamy the predominant marriage form, even in highly unequal societies. We assess if these conditions are satisfied using individual-level data from 29 human populations. Our analysis shows that with the shift to stratified agricultural economies: (i) the population frequency of relatively poor individuals increased, increasing wealth inequality, but decreasing the frequency of individuals with sufficient wealth to secure polygynous marriage, and (ii) diminishing marginal fitness returns to additional wives prevent extremely wealthy men from obtaining as many wives as their relative wealth would otherwise predict. These conditions jointly lead to a high population-level frequency of monogamy.

While recent studies suggest children can use cross-situational information to learn words, these studies involved minimal referential ambiguity, and the cross-situational evidence overwhelmingly favored a single referent for each word. Here we asked whether 2·5-year-olds could identify a noun's referent when the scene and cross-situational evidence were more ambiguous. Children saw four trials in which a novel word occurred with four novel objects; only one object consistently co-occurred with the word across trials. The frequency of distracter objects varied across conditions. When all distracter referents occurred only once (no-competition), children successfully identified the noun's referent. When a high-probability competitor referent occurred on three trials, children identified the target referent if the competitor was absent on the third trial (short-competition) but not if it was present until the fourth trial (long-competition). This suggests that although 2·5-year-olds' cross-situational learning scales up to more ambiguous scenes, it is disrupted by high-probability competitor referents.

Children and adults can use cross-situational information toidentify words’ referents. What do learners retain about thepotential referents that occur with a word: do they encodemultiple referents or a single guess? We tested this questionusing novel mouse tracking and finger tracking paradigms.Adults were exposed to novel words in a series of ambiguoustraining trials and then tested on the words’ referents. In sometest trials, participants saw the target and three referents thathad never occurred with the word; other test trials included ahigh-probability competitor that had repeatedly occurred withthe word. Participants’ mouse movements were slower, lessaccurate, and took a more complex path to the selectedreferent when the competitor was present, indicating thatparticipants were aware that both the target and competitorhad previously occurred with the word. This suggests thatlearners can accrue information about multiple potentialreferents for a word, and that mouse tracking provides apromising way of assessing this knowledge. However, thisknowledge was not evident in participants’ finger movements,suggesting that the dynamics of finger movements might notcapture real-time competition between referents.

While recent studies suggest children can use cross-situational information to learn words, these studies involved minimal referential ambiguity, and the cross-situational evidence overwhelmingly favored a single referent for each word. Here we asked whether 2-5-year-olds could identify a noun's referent when the scene and cross-situational evidence were more ambiguous. Children saw four trials in which a novel word occurred with four novel objects; only one object consistently co-occurred with the word across trials. The frequency of distracter objects varied across conditions. When all distracter referents occurred only once (no-competition), children successfully identified the noun's referent. When a high-probability competitor referent occurred on three trials, children identified the target referent if the competitor was absent on the third trial (short-competition) but not if it was present until the fourth trial (long-competition). This suggests that although 2-5-year-olds' cross-situational learning scales up to more ambiguous scenes, it is disrupted by high-probability competitor referents.