Your skin cell is really useless without a heart cell, muscle cell, a brain cell and so on. So these communities began to evolve so that the interesting level on which evolution was taking place was no longer a cell, but a community which we call an organism.
La célula de la piel no sirve sin la del corazón, o la de los músculos, o la del cerebro, etc. Así, estas comunidades evolucionaron y se produjeron niveles más interesantes que el celular, algo que llamamos un organismo.