What Is Biological Immortality And Why Human Cells Are Not Immortal?

What is the difference between immortality and biological immortality? "Immortal means you don't die at all," answers Thomas Bosch at the University of Kiel. No living organism that can not be destroyed by external forces has ever been found. In that sense, there are no immortal organisms. 

However, some cells and organisms have, what is called, biological immortality: they are not susceptible to apoptosis, intracellular mechanisms that cause cell death. It means that if no external force causes them damage, they can continue their existence because there are no internal forces to bring them to their end. 

How Does Human Cell Aging Work?

Why exactly are normal human cells innately mortal - why our bodies age? First of all, are structures at the end of the chromosomes called the "telomeres." In humans, chromosomes irreversibly lose some part of their telomeres every time a human cell divides. Essentially, it starts from the moment our cells differentiate from the form of the stem cells and keeps happening as we grow and age. Cells keep losing telomers until they reach the point where cells can no longer divide: in scientific terms, enter synesthesia. 

Siphonophores take it one step further as they can make several different kinds of basic units in the same colony. All units are genetically identical, and all come from one founding individual. The main difference is that in corals, all colony units are functionally and physically identical. In the siphonophores, there is a fundamental differentiation of units, each specializing in a particular task. Some zooids are adapted for swimming, some for feeding, reproduction, hunting, etc. Moreover, as they are suited for that one task, so they would not survive on their own. However, it appears siphonophores can keep budding and replacing their units without limit, hence maintaining the "immortality" of the genetic individual.