As the title suggests, biologist, and scientist in general, are (so far as we know) all people. This means that they have biases and preferences just like any other person. In fact, the main thing that separates scientific inquiry from other ways of finding out about the world is that science is structured to minimize individual bias as much as possible and to make it easier to detect when it is present. There are two things to address in this discussion:
How can researchers bias their results, and how does a scientific approach minimize that bias.
Your textbook gives you many examples of research and ideas associated with particular people. Select one of those and speculate on how the person doing the research might have preferred a particular result, and then discuss how that potential bias could have been neutralized.