Herculano-Houzel Suzana, Kaas Jon H
Instituto de Ciências Biomédicas, Universidade Federal do Rio de Janeiro, and Instituto Nacional de Neurociência Translacional, Rio de Janeiro, Brazil.
Brain Behav Evol. 2011;77(1):33-44. doi: 10.1159/000322729. Epub 2011 Jan 11.
Gorillas and orangutans are primates at least as large as humans, but their brains amount to about one third of the size of the human brain. This discrepancy has been used as evidence that the human brain is about 3 times larger than it should be for a primate species of its body size. In contrast to the view that the human brain is special in its size, we have suggested that it is the great apes that might have evolved bodies that are unusually large, on the basis of our recent finding that the cellular composition of the human brain matches that expected for a primate brain of its size, making the human brain a linearly scaled-up primate brain in its number of cells. To investigate whether the brain of great apes also conforms to the primate cellular scaling rules identified previously, we determine the numbers of neuronal and other cells that compose the orangutan and gorilla cerebella, use these numbers to calculate the size of the brain and of the cerebral cortex expected for these species, and show that these match the sizes described in the literature. Our results suggest that the brains of great apes also scale linearly in their numbers of neurons like other primate brains, including humans. The conformity of great apes and humans to the linear cellular scaling rules that apply to other primates that diverged earlier in primate evolution indicates that prehistoric Homo species as well as other hominins must have had brains that conformed to the same scaling rules, irrespective of their body size. We then used those scaling rules and published estimated brain volumes for various hominin species to predict the numbers of neurons that composed their brains. We predict that Homo heidelbergensis and Homo neanderthalensis had brains with approximately 80 billion neurons, within the range of variation found in modern Homo sapiens. We propose that while the cellular scaling rules that apply to the primate brain have remained stable in hominin evolution (since they apply to simians, great apes and modern humans alike), the Colobinae and Pongidae lineages favored marked increases in body size rather than brain size from the common ancestor with the Homo lineage, while the Homo lineage seems to have favored a large brain instead of a large body, possibly due to the metabolic limitations to having both.
大猩猩和红毛猩猩是至少与人类体型相当的灵长类动物，但它们的大脑大小约为人类大脑的三分之一。这种差异被用作证据，证明人类大脑的大小比同体型灵长类物种应有的大小大约大三倍。与人类大脑在大小上很特殊的观点相反，我们认为可能是大猩猩进化出了异常大的身体，因为我们最近发现人类大脑的细胞组成与其大小的灵长类大脑预期相符，这使得人类大脑在细胞数量上是线性放大的灵长类大脑。为了研究大猩猩的大脑是否也符合先前确定的灵长类细胞缩放规则，我们确定了构成红毛猩猩和大猩猩小脑的神经元和其他细胞的数量，用这些数量来计算这些物种预期的大脑和大脑皮层大小，并表明这些与文献中描述的大小相符。我们的结果表明，大猩猩的大脑在神经元数量上也像包括人类在内的其他灵长类大脑一样呈线性缩放。大猩猩和人类符合适用于在灵长类进化中更早分化的其他灵长类的线性细胞缩放规则，这表明史前的智人物种以及其他原始人类的大脑一定也符合相同的缩放规则，无论它们的体型大小如何。然后我们使用这些缩放规则和已公布的各种原始人类物种的估计脑容量来预测构成它们大脑的神经元数量。我们预测海德堡人和尼安德特人的大脑约有800亿个神经元，在现代智人发现的变异范围内。我们提出，虽然适用于灵长类大脑的细胞缩放规则在原始人类进化中保持稳定（因为它们适用于猿猴、大猩猩和现代人类），但叶猴科和猩猩科谱系从与智人谱系的共同祖先开始就倾向于身体大小的显著增加而非大脑大小的增加，而智人谱系似乎更倾向于大脑大而非身体大，这可能是由于同时拥有两者存在代谢限制。
