Читать книгу Astrobiology - Charles S. Cockell - Страница 130

The discussion in this chapter should have convinced you that the title of this discussion point is probably too simple. Many prokaryotic and single-celled eukaryotes exhibit behavior that is multicellular, from the swarming activities of slime molds and Myxobacteria to the specialized cells found in some bacteria, such as spores. Nevertheless, it still remains a cogent question to ask ourselves why cells tend to form multicelled structures. Why isn't Earth covered in cells all individually going about their lives? One obvious answer is that energetic needs force collaboration. One microbe's waste can be another one's food, and thus associations will be selected for, as we will see in microbial mats in the next chapter. Cell differentiation, for example the formation of fruiting body cells and swarming cells in Myxobacteria, can be explained in terms of the efficiencies to be gained by specialization, where each particular cell can carry out a function better than a very general cell that must do everything. What about irreversible differentiation, for example in human cells? Imagine a version of yourself where your cells could all break down and spread out looking for food and then regroup? Why did cells give up this versatility? One answer could be that it was energetically favorable for cells to irreversibly commit to certain roles in an organism. Alternatively, perhaps the success of a complex organism like an animal in the environment removes the selection pressure for it to be able to disperse, and those capacities in cells were lost? There are clearly many fascinating questions to be answered. What do you think about the emergence of multicellularity and the steps that led to plants and animals?