The introduction to your paper tells the reader what your study is about, but should also explain why this topic is worth studying. It explains what is already known about the field being investigated, and shows how your study will add to our knowledge.
Linguist John Swales (1984) made a study of introductions in research papers, and found that they typically had four main elements or “moves.”
“Establish the field.” Begin by introducing the general topic of the paper, and showing how research in this field is useful in some way.
“Summarize previous research.” Tell the reader what we knew about this field going into your research.
“Prepare for present research.” Show how your research adds to what we already know. Is there a gap in previous knowledge? Have previous studies left questions unanswered? Perhaps previous studies are ambiguous or contradictory, or perhaps you can improve on the techniques used.
“Introduce the present research.” Explain the purpose of the current research. Outline the hypothesis you tested, and the general approach you took (no details of methods here).
In a biology paper, the introduction generally needs to include both information on general theory, and information on the organism being studied. So for example a paper studying mating dances in the fruit fly Drosophila melanogaster would need to provide background on what is known about animal mating displays in general, but also some natural history of the flies, to help show how the general theory might apply to these organisms. Only information relevant to the research being described should be included. Don’t fill your introduction with “interesting facts about the fruit fly.” For more on what sources to use and organizing your literature search, go here.