guided by the environment.. Guided, that is a purpose filled word. Just who is this environment who leads toward a goal? not random, order. leads to survive ability. leads to organisms. Something that creates life. We used to call Him God.
Most evolution is by genetic drift, not mutation although mutation is very important. There are a great many inheritable variations within a species. Some people have red hair, some are tall, some can digest milk easily. If it benefits people in one region, ( ie being tall to look over grass, using milk as a food by herders, being more attractive to females who like red hair ) that region will have more tall milk drinkers although other traits exist in portions of the population. If the people in that region remain isolated, the differences from the species as a whole will most likely accumulate to the point were the isolated trabecular can no longer breed with the other groups.
Evolutionary change happens most rapidly due to drastic changes in climate (environment). The greatest spur to evolutionary change was the great oxygenation event. All types of multicellular life expanded, protective shells and exoskeletons , etc. developed as life spread into many new areas. 2,600 minerals that hadn’t existed before come into the geologic record.
That’s what I mean by “guided”.