Pretelli, I., Borgerhoff Mulder, M., Makame Khamis, B., & McElreath, R. (2023). Foraging and the importance of knowledge in Pemba, Tanzania: Implications for childhood evolution. Proceedings of the Royal Society B: Biological Sciences, 290(2011), 20231505.

Childhood is a period of life unique to humans. Childhood may have evolved through the need to acquire knowledge and subsistence skills. In an effort to understand the functional significance of childhood, previous research examined increases with age in returns to foraging across food resources. Such increases could be due to changes in knowledge, or other factors such as body size or strength. Here, we attempt to unpack these age-related changes. First, we estimate age-specific foraging returns for two resources. We then develop nonlinear structural equation models to evaluate the relative importance of ecological knowledge, grip strength and height in a population of part-time children foragers on Pemba island, Tanzania. We use anthropometric measures (height, strength, n = 250), estimates of ecological knowledge (n = 93) and behavioural observations for 63 individuals across 370 foraging trips. We find slower increases in foraging returns with age for trap hunting than for shellfish collection. We do not detect any effect of individual knowledge on foraging returns, potentially linked to information sharing within foraging parties. Producing accurate estimates of the distinct contribution of specific traits to an individual’s foraging performance constitutes a key step in evaluating different hypotheses for the emergence of childhood.

Image: Shellfish collection in Pemba, Tanzania.

Pretelli, I., Ringen, E., & Lew-Levy, S. (2022). Foraging complexity and the evolution of childhood. Science Advances, 8(41).

Our species’ long childhood is hypothesized to have evolved as a period for learning complex foraging skills. Researchers studying the development of foraging proficiency have focused on assessing this hypothesis, yet studies present inconsistent conclusions regarding the connection between foraging skill development and niche complexity. Here, we leverage published records of child and adolescent foragers from 28 societies to (i) quantify how skill-intensive different resources are and (ii) assess whether children’s proficiency increases more slowly for more skill-intensive resources. We find that foraging returns increase slowly for more skill-intensive, difficult-to-extract resources (tubers and game), consistent with peak productivity attained in adulthood. Foraging returns for easier-to-extract resources (fruit and fish/shellfish) increase rapidly during childhood, with adult levels of productivity reached by adolescence. Our findings support the view that long childhoods evolved as an extended period for learning to extract complex resources characteristic of the human foraging niche.

Image: foraging proficiency at different ages across resources. Credit: Erik Ringen.

Pretelli, I., Borgerhoff Mulder, M., & McElreath, R. (2022). Rates of ecological knowledge learning in Pemba, Tanzania: Implications for childhood evolution. Evolutionary Human Sciences, 4, e34.

Humans live in diverse, complex niches where survival and reproduction are conditional on the acquisition of knowledge. Humans also have long childhoods, spending more than a decade before they become net producers. Whether the time needed to learn has been a selective force in the evolution of long human childhood is unclear, because there is little comparative data on the growth of ecological knowledge throughout childhood. We measured ecological knowledge at different ages in Pemba, Zanzibar (Tanzania), interviewing 93 children and teenagers between 4 and 26 years. We developed Bayesian latent-trait models to estimate individual knowledge and its association with age, activities, household family structure and education. In the studied population, children learn during the whole pre-reproductive period, but at varying rates, with the fastest increases in young children. Sex differences appear during middle childhood and are mediated by participation in different activities. In addition to providing a detailed empirical investigation of the relationship between knowledge acquisition and childhood, this study develops and documents computational improvements to the modelling of knowledge development.

Image: boys fishing catfish, Pemba, Tanzania.

Other papers

Pretelli, Ilaria, Crittenden, Alyssa N., Dounias, Edmond , Friant, Sagan , Koster, Jeremy, Kramer, Karen L. , Mangola, Shani M., Mari Saez,  Almudena and Lew‐Levy, Sheina. "Child and adolescent foraging: New directions in evolutionary research." Evolutionary Anthropology: Issues, News, and Reviews (2023): e22020, doi: Link to paper About it in the media

Lew-Levy, S., Reckin, R., Kissler, S. M., Pretelli, I., Boyette, A. H., Crittenden, A. N., ... & Davis, H. E. (2022). Socioecology shapes child and adolescent time allocation in twelve hunter-gatherer and mixed-subsistence forager societies. Scientific Reports, 12(1), 8054. Open Access 

Broesch, T., Crittenden, A. N., Beheim, B. A., Blackwell, A. D., Bunce, J. A., Colleran, H., ... & Mulder, M. B. (2020). Navigating cross-cultural research: methodological and ethical considerations. Proceedings of the Royal Society B, 287(1935), 20201245. Open Access 

Caro, T., Hamad, H., Rashid, R. S., Kloiber, U., Morgan, V. M., Nokelainen, O., Caro, B., Pretelli, I., Cumberlidge, N., & Borgerhoff Mulder, M. (2021). A case study of the coconut crab Birgus latro on Zanzibar highlights global threats and conservation solutions. Oryx, 55(4), 556-563. Open Access 

Kenna, D., Cooley, H., Pretelli, I., Ramos Rodrigues, A., Gill, S. D., & Gill, R. J. (2019). Pesticide exposure affects flight dynamics and reduces flight endurance in bumblebees. Ecology and Evolution, 9(10), 5637-5650. Open Access 


Top image: men leave at dusk for night fishing, Pemba, Tanzania.