7.45-7.06 billion years ago.
No big news in the universe today. Some evolutionary thoughts: Species evolve. Do planets? stars? galaxies?
Charles Darwin didn’t use the word “evolution” often. But he did write a lot about “descent with modification,” which is pretty much what biologists mean by evolution. For example, the usual definition of genetic evolution is “change in gene frequency,” i.e. descent with (genetic) modification. And Darwin argued that all living things belong to one or a few family trees linked by recent or remote common descent.
Recently, some astronomers teamed up with some evolutionary biologists to produce a “family tree” of our Sun and some of its neighbors. The tree is based on the abundances of different chemical elements; these abundances don’t change much over the lifetime of a star, and can be thought of as a kind of inherited trait, something like DNA. The tree groups stars roughly according to their ages, with younger stars having more “metals” (elements other than hydrogen and helium), but only roughly, since other processes affect stellar chemistry.
Drawing a family tree for stars might seem like an odd thing to do. In what sense are stars related as parent and offspring? Evolutionary biologists face a similar situation where group selection is concerned. Suppose you have a population of organisms. Those organisms form groups that last for a time and disband, with their members “seeding” the population at large, and influencing group formation in the next generation. Although there are ancestor-descendant relations between individual organisms, you can’t identify any one group in generation T+1 as the descendant of any particular group in generation T. Are the groups in this case meaningful evolutionary units? It depends on which biologist you talk to.