The average lifespan of a lab mouse is 2.5 years.

That of a human is 80 years.

That of a bowhead whale is 200 years.

Now we take a few stem cells from a mouse and a human, culture them in a petri dish, and ask them nicely to differentiate into neurons. Mouse cells take a few days, while human cells take a few weeks.

How do cells count time? Why human speed is much slower than mouse?

The rate-of-living theory, created by Max Rubner over a century ago, states that the faster an organism's metabolism, the shorter its lifespan. I'm wondering if there is a causal relationship somewhere. My Ph.D. thesis project investigates how developmental tempo is regulated in human embryonic stem cells (hESCs) and how we can speed it up or down by modulating certain molecular pathways.