Aboitiz F
Neuroscience Program, Brain Research Institute, University of California, Los Angeles 90024-1761.
Biol Res. 1992;25(1):41-9.
The origin of the mammalian neocortex in usually considered as an improvement in the structure of the brain. Alternatively, I suggest that the mammalian neocortex arose as a consequence of contingent adaptations in which there was no specific selection for more elaborate cognitive abilities. In primitive mammals, the adaptation to nocturnal life produced a reduction of the optic tectum (superior colliculus). In addition, the development of the olfactory system triggered the development of the cerebral cortex. It is proposed that, since both the optic tectum and the cerebral cortex are laminar structures, the growing cortex replaced the tectum in many integratory functions. When mammals reinvaded diurnal niches, the optic tectum did not redevelop, and the cerebral cortex remained the main integratory and perceptual system. This is a case of irreversible reduction of an organ. In reptiles and especially in birds, although there was also an increase in brain size (associated with higher cognitive capacities), the optic tectum grew in size and complexity and the forebrain grew largely as a nonlaminar structure (except the Wulst in birds). Therefore, the origin of the cerebral cortex resulted from the combination of adaptations to nocturnality and the development of olfactory-driven behavior, and its origin is not directly related to higher cognitive capacities.
哺乳动物新皮层的起源通常被认为是大脑结构的一种改进。然而，我认为哺乳动物新皮层的出现是偶然适应的结果，在这些适应过程中，并没有对更复杂的认知能力进行特定的选择。在原始哺乳动物中，对夜行性生活的适应导致视顶盖（上丘）缩小。此外，嗅觉系统的发育引发了大脑皮层的发育。有人提出，由于视顶盖和大脑皮层都是层状结构，不断生长的皮层在许多整合功能中取代了视顶盖。当哺乳动物重新进入昼行生态位时，视顶盖没有重新发育，大脑皮层仍然是主要的整合和感知系统。这是一个器官不可逆缩小的例子。在爬行动物尤其是鸟类中，尽管脑容量也有所增加（与更高的认知能力相关），但视顶盖在大小和复杂性上都有所增长，前脑主要作为非层状结构生长（鸟类的视叶皮质除外）。因此，大脑皮层的起源是对夜行性的适应和嗅觉驱动行为发展相结合的结果，其起源与更高的认知能力没有直接关系。
