Statistics show that in humans, and in other mammals as well, females live longer then males and are more able to fight off shock episodes such as infection, sepsis, or trauma. The researchers tried to find the explanation for this phenomenon and they recently concluded that this is due to the X-chromosome, whose biological mechanisms have a strong impact on individual's genes. That is because the X- chromosome contains 10% of all micro RNAs which have important functions in immunity and cencer. Micro RNA is tiny strands of ribonucleic acid, which together with DNA, and proteins make up the three major macromolecules that are essential for all known forms of life. The role of micro RNAs encoded on the X- chromosome is such that it obviously impacts immune system in a way that is less likely to develop cancer and is more able to fight off shock episodes. This leaves males at an immunological disadvantage as a male has only one X-chromosome and Y- chromosome contains fewer genes.