Stable carbon isotopes and human evolution

Evolutionary ecology of language origins through confrontational scavenging

A dynamic model and an agent-based simulation model implementing the assumptions of the confrontational scavenging hypothesis on early protolanguage as an adaptive response of Homo erectus to gradual change in their habitat has been developed and studied. The core assumptions of the hypothesis and the model scenario are the pre-adaptation of our ancestors to occupy the ecological niche that they constructed for themselves by having evolved displaced communication and a rudimentary tool manufacture, two features allowing them to use a new, concentrated and abundant resource-megafauna carrion-on the savannahs replacing arboreal habitats owing to the drying climate of East Africa at about 2 Ma. The shift in diet required coordinated cooperation by the hominin scavengers confronted with concurrent predators. Power scavenging compelled displaced symbolic communication featuring a limited semantic range; syntax was not yet required. We show that phenotypic evolution on the accuracy of information transfer between cooperating hominins is a necessary and sufficient condition for the population of agents to survive the diet shift. Both the individual and the group fitness of the hominin horde increased with the accuracy of their protolanguage, with decreasing time allocated to foraging and thus more time left for culture. This article is part of the theme issue 'Human socio-cultural evolution in light of evolutionary transitions'.

Environmental drivers of megafauna and hominin extinction in Southeast Asia

Southeast Asia has emerged as an important region for understanding hominin and mammalian migrations and extinctions. High-profile discoveries have shown that Southeast Asia has been home to at least five members of the genus Homo^1-3. Considerable turnover in Pleistocene megafauna has previously been linked with these hominins or with climate change⁴, although the region is often left out of discussions of megafauna extinctions. In the traditional hominin evolutionary core of Africa, attempts to establish the environmental context of hominin evolution and its association with faunal changes have long been informed by stable isotope methodologies^5,6. However, such studies have largely been neglected in Southeast Asia. Here we present a large-scale dataset of stable isotope data for Southeast Asian mammals that spans the Quaternary period. Our results demonstrate that the forests of the Early Pleistocene had given way to savannahs by the Middle Pleistocene, which led to the spread of grazers and extinction of browsers-although geochronological limitations mean that not all samples can be resolved to glacial or interglacial periods. Savannahs retreated by the Late Pleistocene and had completely disappeared by the Holocene epoch, when they were replaced by highly stratified closed-canopy rainforest. This resulted in the ascendency of rainforest-adapted species as well as Homo sapiens-which has a unique adaptive plasticity among hominins-at the expense of savannah and woodland specialists, including Homo erectus. At present, megafauna are restricted to rainforests and are severely threatened by anthropogenic deforestation.

The stable isotope setting of Australopithecus sediba at Malapa, South Africa

Abstract We report δ13C and δ18O results from carbonate-cemented cave sediments at Malapa in South Africa. The sediments were deposited during a short-period magnetic reversal at 1.977±0.003 Ma, immediately preceding deposition of Facies D sediments that contain the type fossils of Australopithecus sediba. Values of δ13C range between -5.65 and -2.09 with an average of -4.58±0.54‰ (Vienna Pee Dee Belemnite, VPDB) and values of δ18O range between -6.14 and -3.84 with an average of -4.93±0.44‰ (VPDB). Despite signs of diagenetic alteration from metastable aragonite to calcite, the Malapa isotope values are similar to those obtained in two previous studies in South Africa for the same relative time period. Broadly, the Malapa δ13C values provide constraints on the palaeovegetation at Malapa. Because of the complex nature of the carbonate cements and mixed mineralogy in the samples, our estimates of vegetation type (C4-dominant) must be regarded as preliminary only. However, the indication of a mainly C4 landscape is in contrast to the reported diet of A. sediba, and suggests a diverse environment involving both grassland and riparian woodland.

Effect of baking and fermentation on the stable carbon and nitrogen isotope ratios of grain-based food

RATIONALE

Isotope ratio mass spectrometry (IRMS) is used extensively to reconstruct general attributes of prehistoric and modern diets in both humans and animals. In order to apply these methods to the accurate determination of specific intakes of foods/nutrients of interest, the isotopic signature of individually consumed foods must be constrained. For example, 86% of the calories consumed in the USA are derived from processed and prepared foods, but the relationship between the stable isotope composition of raw ingredients and the resulting products has not been characterized.

METHODS

To examine the effect of common cooking techniques on the stable isotope composition of grain-based food items, we prepared yeast buns and sugar cookies from standardized recipes and measured bulk δ(13) C and δ(15) N values of samples collected throughout a 75 min fermentation process (buns) and before and after baking at 190°C (buns and cookies). Simple isotope mixing models were used to determine if the isotopic signatures of 13 multi-ingredient foods could be estimated from the isotopic signatures of their constituent raw ingredients.

RESULTS

No variations in δ(13) C or δ(15) N values were detected between pre- and post-baked yeast buns (pre: -24.78‰/2.61‰, post: -24.75‰/2.74‰), beet-sugar cookies (pre: -24.48‰/3.84‰, post: -24.47‰/3.57‰), and cane-sugar cookies (pre: -19.07‰/2.97‰, post: -19.02‰/3.21‰), or throughout a 75 min fermentation process in yeast buns. Using isotopic mass balance equations, the δ(13) C/δ(15) N values of multi-ingredient foods were estimated from the isotopic composition of constituent raw ingredients to within 0.14 ± 0.13‰/0.24 ± 0.17‰ for gravimetrically measured recipes and 0.40 ± 0.38‰/0.58 ± 0.53‰ for volumetrically measured recipes.

CONCLUSIONS

Two common food preparation techniques, baking and fermentation, do not substantially affect the carbon or nitrogen isotopic signature of grain-based foods. Mass-balance equations can be used to accurately estimate the isotopic signature of multi-ingredient food items for which quantitative ingredient information is available.