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Human Brain Expansion during Evolution Is Independent of Fire Control and Cooking - PubMed

  • ️Fri Jan 01 2016

Human Brain Expansion during Evolution Is Independent of Fire Control and Cooking

Alianda M Cornélio et al. Front Neurosci. 2016.

Abstract

What makes humans unique? This question has fascinated scientists and philosophers for centuries and it is still a matter of intense debate. Nowadays, human brain expansion during evolution has been acknowledged to explain our empowered cognitive capabilities. The drivers for such accelerated expansion remain, however, largely unknown. In this sense, studies have suggested that the cooking of food could be a pre-requisite for the expansion of brain size in early hominins. However, this appealing hypothesis is only supported by a mathematical model suggesting that the increasing number of neurons in the brain would constrain body size among primates due to a limited amount of calories obtained from diets. Here, we show, by using a similar mathematical model, that a tradeoff between body mass and the number of brain neurons imposed by dietary constraints during hominin evolution is unlikely. Instead, the predictable number of neurons in the hominin brain varies much more in function of foraging efficiency than body mass. We also review archeological data to show that the expansion of the brain volume in the hominin lineage is described by a linear function independent of evidence of fire control, and therefore, thermal processing of food does not account for this phenomenon. Finally, we report experiments in mice showing that thermal processing of meat does not increase its caloric availability in mice. Altogether, our data indicate that cooking is neither sufficient nor necessary to explain hominin brain expansion.

Keywords: brain size; cooking; fire control; human evolution; thermal processing of food.

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Figures

Figure 1
Figure 1

Theoretical effects of foraging efficiency over the number of brain neurons related to body weight. The graphic predicts the number of neurons in different foraging efficiencies, 500 (dark blue), 1500 (green), 2500 (orange), 3500 (light blue), and 4500 (purple) kcal per day. Ratios of brain and body mass vary from 0.5 to 2%. Species of primates are indicated in the graphic (black circles). Observe that small variations in the body mass are associated with dramatic increases in the number of neurons. A primate with a foraging efficiency of 3500 kcal, such as the gorilla, could easily afford the same number of neurons as a Homo erectus by simply reducing its weight in about 10 kg (red circle).

Figure 2
Figure 2

Augmented foraging efficiency allows increases in body weight, saving daily hours of feeding, and maintaining a great number of neurons. (A–C) Graphics show variations in foraging hours related to body mass for primates supporting 10 (dark blue), 40 (green), 70 (orange), 100 (light blue), or 130 (purple) billion of neurons, in three different foraging efficiencies: 250 kcal/h (A), 500 kcal/h (B), or 750 kcal/h (C). Observe that increasing the foraging efficiency to 750 kcal/h, primates could easily weigh more than 100 kg and have 100 billion neurons spending >5 h in foraging.

Figure 3
Figure 3

Increase in the brain size during human evolution is independent of fire control. (A) Maximal brain volume of different hominin species related to their oldest possible time of origin (Table 1). Data indicate that brain volume increased linearly in time (R2 = 0.8032; p < 0.0001). Colors represent the strength of archeological evidence supporting cooking by hominins throughout the time (C; see also Table 2). (B) Maximal brain volume of different Homo erectus fossils related to their oldest possible time of origin (Table 3). Observe that similar brain volumes of fossils dated from periods with weak and strong evidence for human control of fire. (C) Summary of archeological evidence used to classify the strength of data supporting fire control in hominin lineage. Observe that strong evidence of fire control is present only in the last 790,000 years and archeological data becomes more prominent in the last 400,000 year with Homo neanderthalensis and Homo sapiens. Also, note that species with a maximal brain volume, as large as modern humans', such as Homo erectus, appear at times when no evidence of fire control is present. Legends: a) Aus. Afarensis; b) Aus. Africanus; c) Aus. garhi; d) Aus. sediba; e) Homo rudolphensis; f) Homo habilis; g) Homo ergaster; h) Homo georgicus; i) Homo erectus (Modjokento, Indonesia); j) Homo erectus (Sangiran I, Indonesia); k) Homo erectus (Olduvai, Tanzania); l) Homo lantianensis; m) Homo antecessor; n) Homo cepranensis; o) Homo rhodesiensis; p) Homo heidelbergensis; q) Homo pekinensis; r) Homo neanderthalensis; s) Homo sapiens.

Figure 4
Figure 4

Mice fed with cooked or raw meat present similar weight variations. (A) Relative daily weight variation of mice fed exclusively on a raw meat diet (white squares) or cooked meat diet (black squares). (B) Average amount of meat consumed per day in groups fed with raw (white bar) or cooked (black bar) meat. (C) Absolute weight variation in both raw (white bar) and cooked (black bar) meat diet groups. Note that only on the first day there is a small decrease in the weight of both groups. (D) Correlation between weight variation and meat consumption during 4 days. Observe that the linear regression for the raw meat group (red) is shifted to the left, as compared to the cooked group (blue), indicating that for a similar variation of weight, animals fed on a raw meat diet require a lower amount of meat.

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