  Clearly, this definition, which is the most common and prominent textbook definition, is too narrow to be applied to the range of segments that geneticists commonly call genes and too ambiguous to provide a single, precise partition of DNA into separate genes. Textbooks include many definitions of the gene.  In fact, philosophers have often been frustrated by the tendency of biologists to define and use the term gene in a number of contradictory ways in one and the same textbook. After subjecting the alternative definitions to philosophical scrutiny, gene skeptics have concluded that the problem isn't simply a lack of analytical rigor. The problem is that there simply is no such thing as a gene at the molecular level. That is, there is no single, uniform, and unambiguous way to divide a DNA molecule into different genes. Gene skeptics have often argued that biologists should couch their science in terms of DNA segments such exon, intron, promotor region, and so on, and dispense with the term gene altogether (most forcefully argued by Fogle 2000).