What is a rational and irrational number between 12.1 and 12.2 ?

I can't tell you the irrational number between 0.2 and 0.3; there an infinite number of irrationals in this range.

For an example - root(2) / 7 is slightly more than 0.202, and is irrational.

the answer is; biodiversity resulting from few ancestors

adaptive radiation occurs when a population is subjected to a large natural environment with spatial ecological variations. the parts of the population in the different ecologies begin to adapt to their local environments. due to non-random mating across the large populations, this causes the different populations from the large population to speciate within their local environments. they, therefore, diverge to different species sharing a common ancestor.