A longstanding issue in biology is whether the intelligence of animals can be predicted by absolute or relative brain size. However, progress has been hampered by an insufficient understanding of how neuron numbers shape internal brain organization and cognitive performance. On the basis of estimations of neuron numbers for 111 bird species, we show here that the number of neurons in the pallial telencephalon is positively associated with a major expression of intelligence: innovation propensity. The number of pallial neurons, in turn, is greater in brains that are larger in both absolute and relative terms and positively covaries with longer post-hatching development periods. Thus, our analyses show that neuron numbers link cognitive performance to both absolute and relative brain size through developmental adjustments. These findings help unify neuro-anatomical measures at multiple levels, reconciling contradictory views over the biological significance of brain expansion. The results also highlight the value of a life history perspective to advance our understanding of the evolutionary bases of the connections between brain and cognition.

生物学中一个长期存在的问题是动物的智力是否可以通过大脑的绝对大小或相对大小来预测。然而，由于对神经元数量如何影响内部大脑组织和认知表现的理解不足，进展受到阻碍。基于对 111 种鸟类神经元数量的估计，我们在此表明​​，大脑皮层端脑中的神经元数量与智力的主要表现形式呈正相关：创新倾向。反过来，在绝对值和相对值都较大的大脑中，pallial 神经元的数量更多，并且随着孵化后发育期的延长呈正相关。因此，我们的分析表明，神经元数量通过发育调整将认知表现与绝对和相对大脑大小联系起来。这些发现有助于统一多个层面的神经解剖学措施，调和关于大脑扩张的生物学意义的矛盾观点。结果还强调了生命史观点的价值，以促进我们对大脑与认知之间联系的进化基础的理解。