We all know sex sells, but what about sex cells? Unlike plants and primitive animals, mammals have germlines, specific cells formed during gestation that are distinct from the other cells in the body. The reason for this has been debated, but a new study describes it as necessary to protect mitochondria from the build-up of mutations.
In vertebrate animals, and many invertebrates, the germlines form the eggs and sperm that will make future generations. Plants and simpler animals, such as sponges, produce their sex cells later in their development from the cells that make up other tissues in the body.
“There have been many theories about why mammals have a specialized germline when plants and other ancient animals don’t. Some suggest it was due to complexity of tissues or a selfish conflict between cells. The distinction between sex cells and normal body tissues seems to be necessary for the evolution of very complex specialized tissues like brain,” said Arunas Radzvilavicius, a PhD student at University College London, in a statement.
In PLOS Biology, Radzvilavicius sets out an alternative theory: The reason we need a germline is to provide future generations with the best mitochondria.
Mitochondria are often described as the cells’ power stations, producing the molecules that act as energy sources within cells.
Rates of mitochondrial mutation vary significantly between different life forms. In plants, for example, these rates are low. When tissue cells divide, some receive a larger dose of mutant mitochondria than others. When, as is usually the case, the mutation is harmful, natural selection weeds these out.