INITIAL DARWINIAN ANCESTOR

摘要

In the beginning was Ida, the initial Darwinian ancestor-the first material on Earth to transform from inert to, well, ert. Ida begat Luca, the last universal common ancestor, a molecule that stored information as genetic code, and gave rise to all life on Earth. Ida and Luca live on within us. Our cells all use the same genetic code embodied in DNA, suggesting Luca was itself made of DNA. Except it isn't that simple. All life uses proteins to make DNA and execute its code - but proteins themselves are made from DNA templates. Which came first? Probably neither. RNA is a close relative of DNA found in all living cells that also carries genetic code and, crucially, can catalyse chemical reactions on its own. The RNA world hypothesis says Luca was born out of an RNA soup that eventually gave rise to DNA and the first cells.