Developmental programs are conserved across mammals, but the developmental pace varies between species. Stem cell models have revealed that human neural progenitors develop more slowly than the mouse counterpart due to reduced protein degradation rates. Key questions remain about species-specific protein half-lives, its impact on overall protein levels, and the regulation of protein production and degradation during development. The effect of manipulating individual protein stability on developmental pace is also unclear. Here we analyzed protein production, degradation, and abundance in mouse and human neural progenitors using targeted protein labeling, proteomics, and functional genomics. We identified species differences in protein turnover and found that both active degradation influence tempo divergence between mouse and human. Moreover, proteolytic degradation of a key regulatory protein was shown to affect developmental pace. Our study stresses the role of protein degradation in controlling developmental tempo, with implications for phenotypic diversity across evolution.