Humans want to avoid disease and some diseases can causes holes or hole-like symptoms on victims, so it's human nature to be horrified of clusters of holes because it's abnormal.
I guess it is not widespread because the evolutionary pressure only evolved it on part of human people for local reasons.
Or what I want to believe: Its phenotypical expression is different for different folks because of gene activation. Could be that traumatic occurences in the past (like being serious sick of s.th. like that, or being in the midst of an epidemy, while avoiding it oneself) activate the gene and this is passed on to the next few generations.
I've had arachnophobia (spiders). It feels like an intense, paranoid, startling horror which demands visual attention and quick jumping away of the body. If I know there's a spider nearby, I must be able to see it from a safe distance.
I have trypophobia (holes). It feels like my skin is crawling, like I'm being eaten alive from the inside, like my very essence of being is being violated by some cosmic plague, commanding me to look away and get as far away from the holed object as possible -- though without excessive urgency.
I can look at many things I dislike; many things I know for fact are dangerous. I can't look at certain kinds of clusters of holes.
Please don't feel obliged to answer this, but - is it only biological-looking pictures that trigger this? Or do you get it from clearly non-biological things (eg. security mesh, ventilation grills, cheesegraters) as well?
You really don't encounter something that satisfies all of these naturally very often. Pretty much never. But it doesn't have to be "biological", it can be bread or plastic or anything else.
This reaction is almost certainly a taught cultural behaviour.
In some areas of the world, snakes/spiders are considered food sources. Many of these areas, such as the amazon, also contain the highest concentrations of venomous species.
There was a video that presented images very quickly and asked you to count spiders and snakes percentages among innocent pics. Most respondents (me included) evaluated to at least 50%, while real ratio was something like 1/5 or less. Also, when you watch it, it feels like snake-spider-snake-grass-spider-snake. You may not run in panic, but you do see it.
Cannot find the video, and it was probably a gif, afair.
On the other hand, chimpanzees raised in captivity have been known to scream in fear when seeing snake-like objects such as pieces of hose.
As far as I can tell, not being afraid of them has to be learned. I cannot find a source, but I recall reading that even people who keep spiders as pets, still have a raised heartrate when holding them.
There is a major environmental/learned aspect to this, I don't buy the 100% inborn argument at all. Young children (0-12mo) don't give a damn about anything. I do believe we are born with the innate potential to focus on these creatures faster/earlier than other animals, but fear, that's learned.