Research has identified a species from the west coast of the United
States which may have been the ancestor of 28 distinct species on the
Hawaiian Islands. What is this species?

The species that research has identified a species from the west coast of the United  States which may have been the ancestor of 28 distinct species on the  Hawaiian Islands.

Is:

The Muir tarweed

Explanation:

Research found that the Muir tarweed, a plant species from the west coast of the united states developed into 28 different species in a process that took it thousands of years. The reason behind this is that different mutations made them change slightly and differentiate themselves from the rest, however, the fertility and their reproduction made them evolve in so many kinds.

answer: the blood-brain barrier is a layer of specialized membranes and cell processes designed to keep undesirable substances from passing from the bloodstream into the precious tissues of the brain. while the blood-brain barrier does keep most bad things out of the central nervous system, it is not impermeable.

explanation:

hi~~

i would say that hybridization occurs frequently in nature, because there are many types of hybrids that have occurred naturally, such as the mule (male donkey + female horse)