How might the h1n1 virus have spread so quickly throughout the world

The h1n1 virus spread so quickly because of people. People are traveling with this virus which spreads it and makes it easier for someone to catch. Just as any other influenza virus would spread.

Hi! after fertilization occurs, the zygote goes through mitosis and then differentiation (aka specialization of cells) to have a variety of cells that perform different functions. this allows for the creation of tissues and so on, all of which were once stem cells with no specific function.i hope i !