Read the following passage and answer the item that follows. Your answer to this item should be based on the passage only.

Natural selection has no foresight: it can only favour traits that already exist within a population when a new pressure, a novel pathogen, a changed climate or a new predator, arrives, never traits a species might need decades later. This is why, in modern terms, resistance to an antibiotic already circulating at low levels in a bacterial population can spread rapidly once that antibiotic is used widely, while a bacterium cannot evolve resistance to a drug it has never encountered in anticipation of that drug's future invention. Extinction, on this view, is not a failure of some species to try hard enough; it is simply what happens when a population's existing genetic variation does not happen to include a trait suited to a pressure it did not evolve to expect.

Based on the passage, the following assumptions have been made:

1. A population can only respond to a selective pressure using variation it already possesses.

2. Every bacterial population will eventually develop resistance to every antibiotic that exists.

3. Extinction reflects an absence of suitable existing variation rather than insufficient effort by a species.

Which of the above assumptions is/are valid?