What causes a chemical bond to form between atoms

According to the loco mass the mass of reactants and products

Glucose is a form of sugar found in the blood cells use glucose as a source of energy, but too much or too little can cause serious health issues so, the body uses the hormone insulin to regulate glucose n the blood insulin maintain glucose levels in the blood if blood glucose lovels got very high, what would you expect to see happen to insulin levels?

In general, characteristics that an organism survive and reproduce become more common over time. what mechanism of evolution causes this?