Hormones are secreted and released into the blood by Endocrine glands. Endocrine glands are glands of the endocrine system that secrete their products, hormones, directly into the blood rather than through a duct. The major glands of the endocrine system include the pineal gland, pituitary gland, pancreas, ovaries, thyroid gland, parathyroid gland, hypothalamus and adrenal glands.
Some individuals are more likely to survive and reproduce than others because they are fit and easily adapting. This idea is called 'survival of the fittest'.
