This article illustrates a didactic proposal about evolution theory by natural selection. Evolution helps us to understand the history of life. The central idea of biological evolution is that all life on Earth shares a common ancestor. Through the process of descent with modification, the common ancestor of life on Earth gave rise to the fantastic diversity that we see documented in the fossil record and around us today. Some of the variations found in a species are inherited by offspring from their parents. Since most offspring do not survive the harsh realities of the natural world, organisms have to struggle for survival. We now know these variations are based on different genes carried by the organisms. Only those organisms that do survive long enough to reproduce are then able to pass on their characteristics to their offspring. Thus, in time, characteristics that allow organisms to survive and reproduce become more common. Those that do not will disappear. And so the population evolves. For the teacher the difficulties are: 1) higher complexity of the subject than the target; 2) different disciplinary area of provenance of teachers; 3) teachers' different levels of acceptance of the theory; 4) traditional "methodologies" of science teaching; and 5) scarce availability of teaching aids application. It is necessary that pupils get familiar with this theory since as possible/while they are still at school, because difficulties are many. Most common misconceptions are: a) evolution is just a theory; b) evolution is progress/improvement of the species, from the most simple to the most complex (and perfect), of which man is the apex; c) natural selection implies that individuals strive to adapt; d) the subject of evolution is the individual; and e) evolution is random. The importance of teaching evolution and its difficulties was directly experienced by a didactic intervention in the middle school (14 years-old students). It was an educational project of 7 hours, which included an historical and laboratorial approach. This was based on a student-centered teaching model, because several studies demonstrate that "traditional" teaching is not effective: students learn better by doing than by listening to ex cathedra lessons. Moreover students' inquiries were the driving force for learning, as suggested by IBSE. We chose to use an historical teaching approach to promote students' motivation and understanding, as well as many different techniques to meet every student's needs. The brainstorming technique lets us understand the misconceptions about evolution; the problem solving techniques, applied to real situations, promoted the great importance of understanding evolution; debates and working in team imitated the real operating of the scientific community; use of software for virtual simulations on artificial and natural selection gave the students the opportunity to make comments and experiments on phenomena which normally need too much time. We have tried to involve students through the figure of Darwin and questions that he posed himself. The educational path has sparked interest, for example with regard to the evolutionism-creationism debate. The pre- and post-testing demonstrates the effectiveness of this approach both in overcoming the misconceptions and understanding the evolution theory as well as in stimulating students' inquiries. In addition, it enabled a deep understanding of the nature of science. Results indicate that the use of this approach is promising.
