28. When the inside of the neuron membrane is more positive than the outside of the neuron membrane, it is said to be

In most neurons this potential, called the membrane potential, is between −60 and −75 millivolts (mV; or thousandths of a volt; the minus sign indicates that the inner surface is negative). When the inside of the plasma membrane has a negative charge compared to the outside, the neuron is said to be polarized.

Explanation:

on island x the species needed to adapt because they were being subject to predators which didn't inhabit island y.