Barton Venditti 2014 from Maternal investment, life histories and the evolution of brain structure in primates

Life history is a robust correlate of relative brain size: larger-brained mammals and birds have slower life histories and longer lifespans than smaller-brained species. The Cognitive buffer hypothesis (CBH) proposes an adaptive explanation for this relationship: large brains may permit greater behavioural flexibility and thereby buffer the animal from unpredictable environmental challenges, allowing for reduced mortality and increased lifespan. By contrast, the Developmental costs hypothesis (DCH) suggests that life-history correlates of brain size reflect the extension of maturational processes needed to accommodate the evolution of large brains, predicting correlations with pre-adult life-history phases. Here, we test novel predictions of the hypotheses in primates applied to the neocortex and cerebellum, two major brain structures with distinct developmental trajectories. While neocortical growth is allocated primarily to prenatal development, the cerebellum exhibits relatively substantial post-natal growth. Consistent with the DCH, neocortical expansion is related primarily to extended gestation while cerebellar expansion to extended post-natal development, particularly the juvenile period. Contrary to the CBH, adult lifespan explains relatively little variance in the whole brain or neocortex volume once pre-adult life-history phases are accounted for. Only the cerebellum shows a relationship with lifespan after accounting for developmental periods. Our results substantiate and elaborate on the role of maternal investment and offspring development in brain evolution, suggest that brain components can evolve partly independently through modifications of distinct developmental phases and imply that environmental input during post-natal maturation may be particularly crucial for the development of cerebellar function. They also suggest that relatively extended maturation times provide a developmental mechanism for the marked expansion of the cerebellum in the apes.

生命史（life history）与相对脑容量（relative brain size）存在显著相关性：相较于脑容量较小的类群，脑容量更大的哺乳类与鸟类拥有更缓慢的生命史节奏与更长的寿命。认知缓冲假说（Cognitive Buffer Hypothesis, CBH）为这一关联提供了适应性解释：较大的脑容量可赋予更强的行为灵活性，从而帮助动物抵御不可预测的环境挑战，降低死亡率并延长寿命。与之相对，发育成本假说（Developmental Costs Hypothesis, DCH）则提出，脑容量与生命史的关联实则反映了为演化出较大脑容量所需的成熟过程延长，该假说预测该关联与成体前的生命史阶段相关。本研究以灵长类为研究对象，针对新皮层（neocortex）与小脑（cerebellum）这两种发育轨迹截然不同的主要脑结构，检验这两个假说的全新预测。新皮层的生长主要集中于产前发育阶段，而小脑则展现出相对显著的产后生长。与发育成本假说相符，新皮层的扩张主要与更长的妊娠期相关，而小脑的扩张则与更长的产后发育（尤其是幼年期）相关。与认知缓冲假说相悖，在控制成体前生命史阶段的影响后，成年寿命对全脑或新皮层体积的变异解释度极低。仅小脑在控制发育阶段的影响后，仍与寿命存在关联。本研究结果证实并细化了母体投入与后代发育在脑演化中的作用，表明脑的不同结构可通过修饰不同发育阶段实现部分独立演化，并暗示产后成熟阶段的环境输入对小脑功能发育尤为关键。此外，研究结果还提出，相对更长的成熟时间为类人猿（apes）小脑的显著扩张提供了发育层面的机制解释。