[freespirited]

But there was no metamorphis. DNA didn't change in the survivors from pre-test to post-test.

Perhaps I wasn't clear. We're talking about over subsequent generations. To the contrary, the DNA of the gene pool does change over time.

[muawiyah]

How do we know that? And is it meaningful?

Remember, bacteria can and do borrow genes from other bacteria all the time. We don't know if the aggregate genepool for bacteria in the broadest sense ever change.

[Southack]

"Perhaps I wasn't clear. We're talking about over subsequent generations. To the contrary, the DNA of the gene pool does change over time."

Nope. All that happens is that genes with a pre-existing resistance (or ability to borrow said resistance) survive to propagate.

But the bacterial mat hasn't added new genes because of your experiment. It might shift some genes around, but those genes already existed.

No new aggregate data was introduced into the overall DNA.