life history - Has there been any observation of species adapting the evolution process?

Pigliucci gives a good review of some aspects of this topic in "Is evolvability evolvable?" (2008). He sees what you're asking about, which he calls "evolvability", as one of the key topics for the future of the study of evolution.

It's very conceptually dense evo-devo-theory, so I'll probably do a poor job trying to explain it, but he tries to set up a framework that deals not just with things like life-history (per kmm's answer) and mutation/recombination rate (low fidelity in HIV per GWW's answer, and, I suppose, the evolution of sex itself), but also with constraints that evolve at various levels to "positively channel" mutation (that is, the understanding that while mutations are effectively random, the phenotypes that emerge, and are acted upon by natural selection, are not random, but are channelled by the developmental system of the organism).

He also includes the role of development in opening up "phenotypic space" into which a lineage may evolve. For instance, single-celled organisms have a limit on size and complexity, the evolution of multicellularity opens up this huge zone of evolvability. In a sense, this is also the "evolution of evolution".

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Time from stimulus to gene expression

My understanding is that gene expression, in response to some stimulus, generally occurs on the order of minutes. I'm curious about the extremes...the quickest and the slowest cases.

What is(are) the fastest time(s) recorded for genes being expressed in response to a stimulus? What are the slowest times?

botany - What is the lowest pressure at which plants can survive?

I like your question!

Low surface pressure on Mars (averaging 600 Pa or about 1/170 of Earth's at sea level) is only one difficulty that an organism would have to contend with. In addition, mean surface temperatures are ~210 K (-63 C), the surface ultraviolet flux is extremely high (no ozone layer) and an aridity comparable to the Atacama desert. On the plus side, a 95% CO2 atmosphere might promote photosynthesis.

So, higher plants are extremely unlikely to prosper on Mars. Purely in terms of pressure, experiments suggest that at 1/10 Earth atmospheric pressure vascular plant transpiration increases significantly. So much so that they enter into a drought response which often leads to plant death.

However, lichens may be another matter. These are often adapted to low precipitation/pressure environments such as high mountains. Indeed, this article addresses exactly your question (sadly it is not open access). The authors suggest that the lichen Xanthoria elegans experiences no loss in vitality after 22 days exposure to laboratory Mars-like conditions (low pressure, low temperature etc.)!

Having skimmed this article I am frankly amazed (and slightly dubious) at the result. However, it should be noted that they only ran the experiment for 22 days, applied no ionising radiation (to simulate the high UV flux) and make little mention of the precise metabolic state of the lichen. If it has entered into cryptobiosis (cessation of metabolic processes) then it can't exactly be regarded as prospering.

• de Vera et al., 2010, Astrobiology, 10, 2, Survival Potential and Photosynthetic Activity of Lichens Under Mars-Like Conditions : A Laboratory Study

digestive system - Is it the sphincter that flexes when a human pushes a bowel movement?

Of course the sphincter muscle is at the exit point. To use a toothpaste tube analogy, if I want to squeeze out some toothpaste, it does me little to no good to jostle the nozzle; I need to squeeze the tube (which is analogous to the colon) to get the paste (payload) to come out.

So when a human is sitting on the toilet squeezing, is that squeezing flexing of the sphincter, or squeezing muscles along the sides of the colon pushing on it as one's fingers push on the tube to get toothpaste to come out.

If it's the sphincter that's getting flexed, how is that helping get a big log out?