From researchers at Harvard, here is stunning time-lapse photography of something that (as far as I can see) might or might not be evolution. A bacteria colony spreads out across a giant Petri dish, hits an area with a high concentration of antibiotics, appears to be stopped in its tracks, but then slowly breaches the boundary in a limited area and is soon spreading as before until it reaches an area with an even higher concentration of antibiotics, and the story repeats:
According to the narrator, the barrier is being breached by a small number of antibiotic-resistant mutants, which then reproduce like crazy, at least until they come into competition with other mutants, etc. In other words, evolution.
Now I’m sure this is an extremely naive question, but I hope someone can offer an answer that will leave me less naive: How do we know this is evolution as opposed to learned behavior?
Suppose a given bacterium has several strategies for fighting off the effects of toxins, only one (or a few) of which are succeessful against this particular antibiotic. Most bacteria choose ineffective strategies and die; a few others, by random chance, choose strategies that work. Eventually, other bacteria “observe” that Strategies A,B,C,D,E,F and G keep failing but Strategy H appears to work — and therefore stop using Strategies A,B,C,D,E,F and G and switch over to H, allowing the colony to continue expanding, etc. How, exactly, do these observations take place? I (at least in my current state of naivete) can easily imagine that the bacteria long ago evolved the ability to make such observations, say by detecting chemical evidence that Strategy H has been deployed in certain places where the colony appears to be growing, and that other strategies have been deployed in areas where the colony appears to be dying. I can even imagine that they’ve evolved a mechanism to “deliberately” leave chemical evidence of their choices to make these observations easier for their relatives.
If that’s the story, the bacteria that take over their world at the end of the video can be genetically identically to the ones we see at the beginning. In other words, no evolution takes place over the course of the video.
But the researchers seem quite sure that this is a video of evolution, presumably because they know things I don’t know. Can someone share that knowledge?