Ahormone called overrides the normal sinus rhythm causing the heart to beat faster during the "fight or flight" response.

Epinephrine.

Explanation:

Epinephrine is also known as adrenaline hormone. This hormone can also acts as a neurotransmitter. Epinephrine hormone is released from the adrenal glands.

Epinephrine mainly release at the time fear, stress and prepares the body for the fight or flight response. This hormone increases the heart beat of an individual by overriding the normal sinus rhythm of the heart.

Thus, the answer is epinephrine.

the two answers are a, the population of birds with large beaks will increase on the island, and c, the trait for large beaks will be passed on to future generations through natural selection. the reason for that is because if the birds that have beaks developed for eating small seeds lose all of their food, they will go hungry and eventually starve because they physically cannot eat the large seeds, therefore making the population of large beaked birds higher. also, if the trait of large beaks are dominant on the island over small beaks, then over time the large beaked birds will reproduce more and more, while the smaller beaked birds will reproduce less and less because they can't survive with the food provided. that leads to the trait of small beaks disappearing and the trait of large beaks taking over the island.