Speciation, the formation of new species through evolution, is not usually an event you can directly observe. Organisms typically take many generations to accumulate enough changes to diverge into new species; it's a slow process. In fact, the difficulty of directly observing speciation is a reason cited by skeptics of evolution for why they have doubts.

But biologists working at the University of California, San Diego, and at Michigan State University, may have just put a rest to all of those naysayers. They report to having witnessed the evolution of a new species happen right before their eyes, in a simple laboratory flask, according to Phys.org.

In a month-long experiment using a lambda phage, a virus that infects bacteria but is harmless to humans, they documented the evolution of the organism into two incipient species.

"Many theories have been proposed to explain speciation, and they have been tested through analyzing the characteristics of fossils, genomes, and natural populations of plants and animals," said Justin Meyer, first author of the study. "However, speciation has been notoriously difficult to thoroughly investigate because it happens too slowly to directly observe. Without direct evidence for speciation, some people have doubted the importance of evolution and Darwin's theory of natural selection."

Even the researchers were surprised at how quickly the process unfolded. For the experiment, viruses were cultured along with their favorite hosts, E. coli bacteria. Two different types of cells were included in the study, each with different receptors that the viruses can attach to. This variation provided competition among the viruses, which allowed them to evolve into two different specialized species for each cell type.

"The virus we started the experiment with, the one with the nondiscriminatory appetite, went extinct. During the process of speciation, it was replaced by its more evolved descendants with a more refined palette," explained Meyer.

He continued: "With these experiments, no one can doubt whether speciation occurs. More importantly, we now have an experimental system to test many previously untestable ideas about the process."

Viruses might seem like an odd life form to study speciation with — some philosophers of science question whether viruses should even be counted as life forms — but because they can mutate so rapidly, generations pass at a pace that can be observed. Whether you count them as life or not, there's no doubt that they go through evolution all the same.

It's a fascinating experiment that confirms through observation what Darwin had imagined well over a hundred years ago.