What we are talking about are two whole different levels of viewing the same process, the real difference between "micro" and "macro" evolutions. There is no stretch or jump.

One of these view levels is within a species population, such as one of the "lawns" of bacteria grown in the experiment. At this level we see change in hereditary traits in populations over time: an e.coli. bacteria that is susceptible to the T4 phage has offspring - later generations - that have evolved a trait the parent generation (of one) did not have: resistance to the T4 phage. But if this was all there was to the process of evolution, then you could never have more types of life in one geological age than you had in a previous geological age, and with extinctions, you would be fighting a losing numbers game. There is another key element that takes a larger view to understand.

The other view level is outside all the species populations, looking at all the different populations and the way they each evolve in comparison to the others (even though ALL evolution occurs within each species). At this level we see species evolving to be sufficiently different from older generations that they seem to be like a different species, what is called "arbitrary speciation", although we may not have concurrent populations with the older varieties to say for sure (hence arbitrary). This is useful in talking about long lineages where there are noticeable (to us) differences, however nature itself doesn't worry about such distinctions. We see this with the e.coli. evolution and then the T4 phage evolution, and if we keep the experiment going then we will see similar changes with each one, and that some populations the e.coli. may die out (go extinct).

But this is not all we see, we also, occasionally, see different populations splitting apart and becoming distinct different species, what is called "non-arbitrary speciation", because there is a clear division: in these cases we can clearly identify a parent common ancestor population, and two or more non-interbreeding daughter populations. There is now no force or pressure to keep these daughter populations similar, all the selection pressures will operate on each population differently due to their having non-common mutations since they diverged, and they are free to diverge more and more over time as they accumulate more and more mutations that are advantageous in their respective - but different - environments.

What is a "higher" life form?

Enjoy.