An intervening variable facilitates a better understanding of the relationship between the independent and dependent variables when the variables appear to not have a definite connection. They are studied by means of operational definitions and have no existence apart.
Macroevolution is the process that takes place over several thousands of years and describes how humans have evolved from primates and how reptiles turned into birds. Microevolution leads to small changes in the same species whereas macroevolution leads to the creation of a new species from parent species.
Thus growth can be measured most of the time whereas development may or may not be capable of being measured. Growth takes place within a limited scope of time whereas the scope of development is quite vast. This becomes especially true when it comes to the growth and development of an individual.