Animal evolution is driven by random mutations at the genome level. However, it has long been suggested that there exist physical constraints which limit the set of possible outcomes. In craniate evolution, it has been observed that head features, notably in the genus homo, can be ordered in a morphological diagram such that, as the brain expands, the head rocks more forward, face features become less prognathous and the mouth tends to recede. One school of paleontologists suggests that this trend is wired somewhere structurally inside the anatomy, and that random modifications of genes push up or down animal forms along a pre-determined path. No actual experiment has been able to settle the dispute. I present here an experiment of electric stimulation of the head in the chicken embryo which is able to enhance the magnitude of tension forces during development. This experimental intervention causes a correlated brain shrinkage and rotatory movement of the head, congruent with tissue texture, which proves that head dilation and flexure are intimately linked. Numerical modelling explains why the brain curls when it dilates. This gives support to the idea that there exists, in the texture of the vertebrate embryo, a latent dynamic pattern for the observed paleontological trends in craniates towards homo, a concept known as Inside story.

动物进化是由基因组水平的随机突变驱动的。然而，长期以来人们一直认为存在限制可能结果的物理限制。在颅骨进化过程中，人们观察到头部特征，尤其是人属的头部特征，可以在形态图中排序，这样，随着大脑的扩张，头部更向前摆动，面部特征变得不那么前突，而嘴巴往往会后退。 。一个古生物学家认为，这种趋势在解剖学内部的结构上与某个地方有关，并且基因的随机修改沿着预先确定的路径推动或降低了动物的形态。没有任何实际的实验能够解决这个争议。我在这里提出了一个对鸡胚胎头部进行电刺激的实验，该实验能够增强发育过程中张力的大小。这种实验干预导致相关的大脑收缩和头部旋转运动，与组织纹理一致，这证明头部扩张和弯曲密切相关。数值模型解释了为什么大脑在扩张时会卷曲。这支持了这样一种观点，即在脊椎动物胚胎的结构中，观察到的古生物学趋势中，在脊椎动物胚胎的结构中存在着一种潜在的动态模式，这一趋势被称为“内幕故事”。