The 4 means that you have a 4-fold increase in the number of armadillos. You should use s tringsAsFactors F to create or read your data. Have you considered using any of the established R packages for differential gene expression analysis such as DESeq2 edgeR limmaThese packages will calculate the log-fold-changes for you theyll even do it in a somewhat more sophisticated manner taking the quirks of RNA-seq data into account and.
Sorry if this is a rather basic question.
Then put the equation in Excel Log FC 2 to get the log2. By default this is done using the mean of the unlogged values. I think youre right about Limmas calculation. Function computes fold change between two groups of log2-transformed data foldchange.