In principle, there are many different, chemically diverse ways in which small molecules can be joined together to form polymers. For example, the small molecule ethene (CH₂=CH₂) is used commercially to make the plastic polyethylene (...–CH₂–CH₂–CH₂–CH₂–CH₂–...). The individual subunits of the three major classes of biological macromolecules, however, are all linked by similar reaction mechanisms—that is, by condensation reactions that eliminate water. Can you think of any benefits that this chemistry offers and why it might have been selected in evolution over a linking chemistry such as that used to produce polyethylene?