Hermias had gathered group of philosophers on Assos. Aristotle became the leader of this group. Thanks to his father, he was very interested in anatomy and biology and was a great observer. Aristotle and his group began to collect observations while in Assos, in particular in zoology and biology. He also probably began writing Politics during these years as well as On Kingship, which hasn't survive to this day. Unfortunately, politics once again played a part in Aristotles next move. When the Persiand attacked Assos and captured Hermias, Aristotle escaped with many of his scientists to the island of Lesbos. They remained there for about a year, continuing their research.
In 346BC, Philip had created a treaty with Athens. Three years later, after a year on lesbos, Aristotle and his crew arrived in Macedonia, where he remained for seven years. While many would have you believe he taught a young Alexander the great, that story is probably not true. However, it is possible Philip hoped to place Aristotle in charge of the Academy in Athens, since Speusippus was a strong opponent to Philip. If so, he was not able to make this happen.