Departamento de Psiquiatría, Centro Interdisciplinario de Neurociencias Escuela de Medicina, Pontificia Universidad Católica de Chile, Santiago, Chile.
Prog Brain Res. 2012;195:3-24. doi: 10.1016/B978-0-444-53860-4.00001-5.
Primates are endowed with a brain about twice the size that of a mammal with the same body size, and humans have the largest brain relative to body size of all animals. This increase in brain size may be related to the acquisition of higher cognitive skills that permitted more complex social interactions, the evolution of culture, and the eventual ability to manipulate the environment. Nevertheless, in its internal structure, the primate brain shares a very conserved design with other mammals, being covered by a six-layered neocortex that, although expands disproportionately to other brain components, it does so following relatively well-defined allometric trends. Thus, the most fundamental events generating the basic design of the primate and human brain took place before the appearance of the first primate-like animal. Presumably, the earliest mammals already displayed a brain morphology radically different from that of their ancestors and that of their sister group, the reptiles, being characterized by the presence of an incipient neocortex that underwent an explosive growth in subsequent mammal evolution. In this chapter, we propose an integrative hypothesis for the origin of the mammalian neocortex, by considering the developmental modifications, functional networks, and ecological adaptations involved in the generation of this structure during the cretaceous period. Subsequently, the expansion of the primate brain is proposed to have relied on the amplification of the same, or very similar, developmental mechanisms as those involved in its primary origins, even in different ecological settings.
灵长类动物拥有的大脑大约是同体型哺乳动物的两倍大，而人类的大脑相对于身体大小是所有动物中最大的。这种大脑大小的增加可能与获得更高的认知技能有关，这些技能允许更复杂的社会互动、文化的进化，以及最终操纵环境的能力。然而，在其内部结构上，灵长类动物的大脑与其他哺乳动物有着非常保守的设计，被六层新皮层覆盖，尽管它不成比例地比其他大脑成分扩张，但它遵循相对明确的比例趋势。因此，产生灵长类动物和人类大脑基本设计的最基本事件发生在第一只类灵长类动物出现之前。据推测，最早的哺乳动物已经表现出一种与它们的祖先和它们的姐妹群——爬行动物——截然不同的大脑形态，其特征是存在一个初露头角的新皮层，在随后的哺乳动物进化中经历了爆炸式的增长。在这一章中，我们通过考虑在白垩纪时期生成该结构所涉及的发育修饰、功能网络和生态适应，提出了一个关于哺乳动物新皮层起源的综合假说。随后，提出灵长类动物大脑的扩张依赖于相同或非常相似的发育机制的放大，即使在不同的生态环境中也是如此。
