Orkun

One claim worth being sceptical about since it circulates a lot: that either scheme meaningfully reduces eye strain or protects your vision long-term.

The evidence for that is much weaker than the confident advice suggests. What has better support is unglamorous — blink rate drops when staring at screens, and taking regular breaks and looking at something distant helps. That applies identically in both colour schemes.

Choose based on comfort in your actual lighting. It is one of the few areas where the honest answer really is that personal preference is a legitimate deciding factor.

On the porcupine specifically, since it is the origin of the question: the quills detach extremely easily and the animal reverses into a threat rapidly, so an attacker gets a face full of quills at speed.

From a metre away that looks a great deal like they were fired, which is almost certainly where the cartoon came from. The myth is not invented so much as a reasonable misreading of a fast event.

On predators first: the reasoning is sound and the evidence is suggestive rather than settled.

The hypothesis that visual predation drove a major burst of animal diversification is well known and much discussed — the argument being that once something could see prey at a distance, everything else had to respond, and hard parts, mobility and eyes proliferated together.

What complicates the neat story is that simple light detection is far older and much more widespread than image-forming eyes, and it serves purposes with nothing to do with hunting: day length, depth, orientation to light, avoiding damaging radiation. So the raw material was lying around for a very long time before anyone hunted with it.

The likely picture is that predators drove the transition from detecting light to forming images, rather than inventing photoreception. That is a more modest claim than the popular version and it fits the fossil and genetic evidence better.

The honest answer is that we do not know, and there are three candidate explanations that are not mutually exclusive.

It only happened once. The origin of life may be so improbable that it occurred a single time and everything descends from that event. Under this view there is nothing to compete with because nothing else ever started.

It happened several times and one lineage won. An established biosphere is a hostile place for a fragile new one — the incumbent eats the resources, and quite literally eats the newcomer. A second origin today would be consumed almost immediately by organisms that have had billions of years to get good at consuming things. This is sometimes put as: any new life would be food.

The chemistry is genuinely constrained. Work on alternative replicators suggests that some candidates are markedly worse at the job — less stable, less accurate, harder to assemble. If the chemistry has a strong optimum, convergence rather than accident would explain the uniformity.

My own read is that the second is doing most of the work, but that is a judgement rather than a result.