The theory of natural selection is a crucial topic that any student focusing on population genetics should understand. Here, we provide a broad and simple definition of natural selection, accompanied by examples from the neotropical region. Moreover, the processes and mechanisms by which natural selection alters genetic variation are briefly described. Signatures of selection in living organisms such as plants refer to the observable patterns in the genetic variation of populations that may indicate the action of natural selection. These patterns are the result of specific alleles or genetic variants being favored or disfavored by selective pressures in the environment. Several methods are used by researchers to detect and study these kinds of signatures. The results can provide useful insights into how organisms adapt and evolve in response to their ecological surroundings, as well as providing valuable insights into their response to changes in their environment. Consequently, this can help us comprehend the mechanisms that underlie evolution and ultimately contribute to efforts in conservation and ecosystem recovery. In this chapter, we describe the results obtained from genetic analyses using different molecular markers and genomic sequencing methods, and present case studies involving the neotropical species Euterpe precatoria, Acrocomia aculeata and Bertholletia excelsa. This knowledge is critical for comprehending how these species respond to environmental changes, and for developing effective conservation strategies to preserve their genetic diversity and ecological roles in different ecosystems.