Brains, maturation times, and parenting.
Brains, maturation times, and parenting.
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大脑、成熟时间和养育子女。
DOI：
10.1016/s0197-4580(99)00076-7
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发表时间：
1999
影响因子：
4.2
通讯作者：
Hasenstaub,A
中科院分区：
文献类型：
--
作者：
Allman,J;Hasenstaub,A
芬奇和萨波尔斯基提出，人类婴儿发育缓慢，以及随之而来的对父母的长期依赖，有利于延缓大脑衰老的基因的进化，特别是最近进化出的载脂蛋白E基因的变体。我们在这里研究了人类成熟如此缓慢的可能原因，以及这种缓慢发展对父母依赖和生存模式的影响。大型大脑在能量、解剖结构的复杂性以及达到出生后成熟的特定阶段所需的时间方面都是昂贵的。我们假设，成熟时间成本产生于这样一个事实，即大脑在身体各器官中是独一无二的，需要与环境(学习经验)进行大量互动才能达到成人的能力，因此大脑是控制整个身体成熟的速度限制因素。虽然大脑在比身体其他器官更早的年龄达到成年大小，但它在结构和功能上都不会成熟，直到性成熟之后的某个时候[30]。Flechsig对发育髓鞘形成的经典研究[14，15]表明，大脑的成熟是以循序渐进的方式进行的，例如，从丘脑到初级皮质感觉区，再到颞叶、顶叶和额叶的高级皮质区域。Quartz和Sejnowski[33]提出，大脑根据经验按顺序从一个层次建立到另一个层次，因此较大的大脑可能需要更多的时间才能成熟，部分原因是它们有更多的层次。我们通过分析不同灵长类动物的大脑平均大小和达到出生后成熟的不同阶段所需的平均时间之间的关系，研究了与大脑增大相关的时间成本，例如不同类别的牙齿萌出和生殖成熟。由于大脑和发育时序变量都与身体质量有关，我们首先提取了每个变量的质量统计效应，然后比较了与大脑重量和成熟时间相关的残差值(图1)。作为相对脑大小函数的五个成熟计时关系的接近相同说明了这些关系一致的时钟性质(图2)。值得注意的是，达到每个成熟阶段所需的时间，从婴儿期发生的事件到成年的门槛，都受到相对大脑大小的类似影响。然而，尽管人类达到任何特定成熟阶段所需的绝对时间比任何其他灵长类动物都要长，但人类实际上比我们大脑大小的灵长类动物成熟得更快一些。我们将在稍后的讨论中回到这个有趣的问题上。以妊娠长度衡量，相对大脑大小和产前发育时间之间是否存在类似的关系？这一猜想关系已被提出[38]，并被广泛认为是正确的。图3绘制了灵长类动物的相对大脑大小与相对怀孕时间的关系，很明显，与新生儿和成年动物的大脑大小的关系都非常弱。此前，另一类大脑较大的哺乳动物--齿鲸[27]也注意到，妊娠长度与大脑相对大小之间没有关系。我们的结论是，出生前和出生后的成熟时间在大脑大小方面有很大的不同。与妊娠长度缺乏相关性的一个可能的解释是，胎儿在子宫内相对于其环境处于被动状态，而在出生后发育过程中，…
Finch and Sapolsky propose that the slow development of human infants and their consequent long period of dependency on their parents have favored the evolution of genes that retard brain senescence, specifically recently evolved variants of the apolipoprotein E gene. We examine here the probable reasons why human maturation is so slow, and the influence of this slow development on parental dependence and patterns of survival. Large brains are expensive in terms of energy, anatomic complexity, and the time required to reach particular stages of postnatal maturation. We hypothesize that the maturational time costs arise from the fact that the brain is unique among the organs of the body in requiring a great deal of interaction with the environment (learning experience) to achieve adult competence, and thus that the brain serves as a rate-limiting factor governing the maturation of the entire body. Although the brain achieves its adult size at an earlier age than the other organs of the body, it does not become structurally and functionally mature until some point after sexual maturity [30]. The classical studies of developmental myelination by Flechsig [14, 15] indicate that the brain matures slowly in stepwise hierarchies proceeding, for example, from the thalamus to the primary cortical sensory areas to the higher cortical areas of the temporal, parietal, and frontal lobes. Quartz and Sejnowski [33] have proposed that the brain builds sequentially from one level to the next on the basis of experience, and thus larger brains may require more time to mature, in part because they have more levels. We have examined the time costs associated with enlarged brains by analyzing the relationships between average brain size and the average times required to reach various stages of postnatal maturation, such as the eruption of various classes of teeth and reproductive maturity, in different primate species. Because both brain and developmental timing variables are related to body mass, we have first extracted the statistical effect of mass for each variable and then compared the residual values related to brain weight and maturation times (Fig. 1). The near identity of the five maturation timing relationships as a function of relative brain size illustrate the consistent, clock-like nature of these relationships (Fig. 2). It is remarkable that the times required to attain each of these maturational stages, which range from events occurring in infancy to the threshold of adulthood, are so similarly influenced by relative brain size. However, although the absolute times required by humans to reach any particular stage of maturation are longer than for any other primate, humans actually mature somewhat faster than would be expected for a primate of our brain size. We will return to this interesting point later in our discussion.Is there a similar relationship between relative brain size and prenatal development time as measured by the length of gestation? This conjectural relationship has been proposed [38], and it has been widely assumed to be true. Fig. 3 plots relative brain size versus relative gestation time for primates, and it is evident that the relationships with both neonatal and adult brain size are very weak. A lack of relationship between gestation length and relative brain size has been previously noted for another group of largebrained mammals, the toothed whales [27]. We conclude that there is a major difference between prenatal and postnatal maturation time with respect to brain size. A possible explanation for the lack of correlations with gestation length is that the fetus is in a passive state relative to its environment while in the womb, whereas in postnatal development the …