All mammalian embryos undergo a highly conserved sequence of developmental events, but different species complete this sequence at significantly different speeds. Astonishingly, embryonic development is completed in 15 days in mice, 56 days in humans, and 116 days in elephants ADDIN EN.CITE [1, 2]. However, the mechanisms that regulate developmental rate remain unknown. This gap in our knowledge stems in large part from a lack of simple assays to precisely measure developmental rate in different species. In this project, we propose to leverage an in vitro system that recapitulates the difference in developmental rate between mouse and human. This system provides a quantitative measure of developmental speed as revealed by the period of the segmentation clock, a molecular oscillator associated with the rhythmic production of somites ADDIN EN.CITE [3, 4]. Using this system, we have previously shown that mass-specific metabolic rates are elevated in mouse cells compared to human cells, resulting in accelerated protein production and degradation rates that underlie their accelerated development [4]. This discovery prompted three important questions: (i) Why are basal metabolic rates elevated in mouse cells compared to human cells? (ii) Does metabolism also control the rates of mRNA production, processing and degradation? (iii) Are the same mechanisms conserved in other mammalian species? These questions will be directly addressed by our research aims. We expect to uncover strategies for the manipulation of developmental speed, giving rise to multiple valuable applications. Accelerating the differentiation and maturation of human pluripotent stem cells in vitro would remove a major roadblock in the use of these cells for disease modeling and cell therapy [5]. Moreover, perturbations that slow down the growth of embryonic cells could be applied to limit the proliferation of cancer cells, which often re-activate developmental programs including features of embryonic metabolism ADDIN EN.CITE [6, 7]. Lastly, given the close interconnection of developmental rate and longevity, we expect this work to also shed light on the lifespan determination and aging process [8]. Successful implementation of these scientific aims requires a welcoming and equitable research culture that synthesizes diverse perspectives. Towards this goal, we will also implement DEIA-related aims to recruit diverse researchers, create safe spaces for marginalized trainees, and enhance mentorship at all levels.