You start with one cell. That cell is not resistant. It divides. You have two cells. In all probability neither is resistant. Ditto four cells. As the population grows exponentially, the small probability of a favorable mutation is multiplied by the large number of cells (and perhaps increased by the presence of mutagens). Eventually, in a culture of a billion cells, a few have become resistant. Expose the culture to antibiotics, and the resistant cells survive, and eventually take over the culture.
The possibility of a mixed culture is eliminated by making sure the culture is monoclonal; i.e. - you start with a single bacterium. Any diversity after that has arisen by mutation.
The problem is that no matter how often you explain this (and I've seen the monoclonal culture example explained more than once in the past), they keep bringing up the same refuted argument over and over again, like they don't care that they are repeating a lie if it allows them to badmouth evolution.
Eventually, in a culture of a billion cells, a few have become resistant. Expose the culture to antibiotics, and the resistant cells survive, and eventually take over the culture.
They do not ‘become’ resistant, they ‘are’ resistant regardless if you expose them to antibiotics or not – and if this resistance was not present they would all obviously die once exposed regardless if mutagens were present. To say otherwise is adding a purpose, direction, or plan to evolution. Naturally speaking; nothing becomes ‘resistant’, or is ‘beneficial’, or ‘selects’ anything. It is - or isn’t --- regardless of the situation. There is no ‘choice’ in this matter and basically natural selection boils down to survival and reproduction – that’s it…
(soapbox mode)Honestly, in a naturalistic evolutionary view – life is nothing more than fire in the way it feeds and continues in this fortuitous world it happened upon. It is basically a chemical reaction that started, grew, feeds on the current environment, changes with the wind, and will ultimately burn out. (/soapbox mode)