Читать книгу Astrobiology - Charles S. Cockell - Страница 125

One often sees prokaryotes described in the literature as “primitive.” In the sense that they are simpler than eukaryotic cells, this description is not wrong. However, prokaryotic cells have remarkable features including the ability to move and communicate. We now investigate these characteristics. They are of relevance to understanding the evolution of life on Earth for two reasons. First, they show that the prokaryotes that inhabit the planet today are likely much more complex than the first cells that emerged on Earth. We should therefore be careful when we think of these organisms as “primitive” and recall that there has been at least 3.5 billion years of evolution since life emerged. At the same time, many features across cell types are conserved and seem ancient, such as the genetic code, whose commonality across life suggests that certain cellular structures reflect early events in cellular evolution. Second, learning about these cellular features is an important part of grasping that prokaryotes are not just simple bags of fluid that take in nutrients and excrete waste; single-celled structures can evolve remarkably complex behaviors. This tells us that there is potentiality for great complexity in even the simplest cellular structures.