You refer, then, to the origin of species - something that was central to Darwinism, but is not included in the modern definition of Evolution. Evolution is currently defined as the change in allele frequencies of a population.
"Change in allele frequency" means that children have a different DNA sequence than their parents. "Population" refers to a group of organisms that can interbreed and produce fertile offspring. That is not possible between species.
Of course descent with modification, and thereby the origin of new species as a consequence of evolution, is accepted by biologists. But I want to make clear it is an inductive conclusion from the process of evolution, and is not included in the definition of evolution itself. It is a very important distinction to understand, as I said near the beginning of this article. And it does get confusing as biology works with both the field of Evolutionary Biology and the mechanism of Evolution, and is lax about keeping those two things separate. Again, it's not a fatal problem. My own field has similar problems.
Why is that important? Because grasping that distinction means biologists must accept the possibility that life had multiple origins. In fact, most biologists now accept that there were multiple origins. What they conclude, however, is that all of those origin events either merged or died out such that there is a point in history where a single population can be identified (LUCA) from which all currently existing life evolved.
Why do they conclude that? It's not an unreasonable conclusion, but at the same time it's a pretty weak position. In fact, some biologists have started to challenge that conclusion, which I find very exciting.
