If each specialized cell has the same DNA, how does a cell know that it is supposed to be a cardiac cell, or a nerve cell, or a stomach cell, etc.?

Alaska and northern canada have a diet rich in vitamin d and their skin color is darker than predicted on the basis of iv intensity at their latitude. explain the observation:

The diagram shows a fossil of an ancient whale skull and a skull of a present-day whale. the ancient whale is extinct and is believed to be an ancestor of the present-day whale. what do these skulls most likely show that supports darwin’s theory of evolution? all populations can adapt and survive. only some organisms have a common ancestor. populations change slowly over time. populations rapidly become extinct.

About how many years does it take for one cycle of surface water to become deep water and then surface water again in the oceans? 101001,000