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.
Macroevolution: Change above the species level NABT 2006 Evolution Symposium Introduction The basic concept of evolution â change over time â can be examined in two different time frames. The first, which considers the time period covering a few generations for a population, is microevolution. There are many examples of microevolution that are handy for teaching, such as drug resistance (NESCent 2006a) and changes in beak size of finches in the Galapagos (NESCent 2006b).