Can mean,standard deviation of different populations be similar?

Perhaps this is too obvious but I don't see it. We're analyzing a gene expression dataset of 64 autistic individuals vs 82 normally developed individuals. This dataset is used in this paper here: paper We find that the mean and standard deviation of the (log normalized) data from each group is almost exactly the same. A previous question using this data was asked here: how to interpret normal plot shaped like sigmoid

The plots comparing mean (x-axis) and std. deviation(y-axis) for two groups above look as below: • Why shouldn't it? Mean number of legs in human (or any other specie) males and females is exactly the same, you can find a number of other properties like this.
– Tim
Nov 27 '18 at 9:25
• @Tim thanks :) but then,if those are the only features (legs) available, then we have no means to discriminate between the 2,isn't it?Here,we have 54000 genes.If the mean and sd of the genes in each population group is same,then,this means the genes are not useful for differentiating between these 2 groups of people,is it not? Nov 27 '18 at 9:46
• I guess the genes are correlated, am I correct? So the "effective" number of them is smaller. Random link from the web told me that I'm 99.5% similar to any other human in terms of genes and ~97% to chimpanzees, and 60% to flies, so I guess it could be hard to spot the difference based on some global summary statistics...
– Tim
Nov 27 '18 at 9:54
• That the mean and sd distribution are similar does not mean that at individual level of the genes there might be a lot of differences (which is the basis of all the differential expression analysis).
– llrs
Nov 27 '18 at 11:02
• @llrs ok,thank you.Can you please provide a good reference textbook for differential gene expression analysis with R/matlab/python ? Nov 27 '18 at 11:12