There is shyness that relates to cautiousness around potential perceived humiliation which also has some antisocial connotation to it and relates to low self esteem and shame but it takes the shape of social anxiety which is like an extreme state of shyness.
So when it comes to evolution and how we've turned out, you hafta remember - modern civilization is not something our brains are equipped to handle. Up until very
very recently, most people would be dead by age 25. And your day-to-day life would be consumed with survival tasks. Concepts like "low self esteem" - as odd as it sounds! - are something I consider to be something of a luxury of modern civilization. We have the leisure (and safety) to overthink things, and this is quite a new development.
My brother once went on an extended camping trip for several months, he couldn't believe how busy he was from sunup to sundown. And, this is with getting regular drops of food and supplies and having all sorts of tools and equipment that our ancestors couldn't dream of.
This is why I always say: our brains make more sense in the environment in which they spent millions of years evolving. We're stone age machines, and hm I somehow doubt there was a lot of 'life dissatisfaction' in the stone age ;) (Also you talk about shyness from being naked around someone, well when our brains developed the ability to process 'shyness' clothing certainly didn't exist!)
Here I just did a google, all sorts of people claim being shy is an evolutionary advantage. This is just the first results but plenty more:
Are you shy and think this is a weakness? You may be looking at shyness the wrong way. According to the latest research, somewhere between 40 and 60 percent of all adults report being shy. And while it’s easy to get down on yourself when you are shy or socially anxious, there are times when it’s...
www.truity.com
"If you're used to thinking of your shyness as something wrong with you, know this: shyness is not a personality mistake, but an evolutionary advantage. According to evolutionary psychologists, the tendency to fear and avoid strangers is hardwired into our psyche."
Considering how much we compete with other humans / tribes, being fearful around other humans seems quite reasonable to me. I dunno I am certainly not an evolutionary psychologist, I'm just someone who enjoys thinking about these sorts of things, thanks for asking the question! :)
P.S. Shyness seems to be somewhat instrumental to set boundaries. Cats are very aware of boundaries and they dont seem to like being watched while on the toilet. As humans boundaries are no doubtly beneficial and if sexual shyness is natural vs nurtured then could it be that as humans we are supposed to be very aware and reserved as to when we select our mates and consciously have difficult time letting someone in too close until we get to know them well and there is a sense of trust. Maybe when shyness becomes no issue with unfamiliar partners it could be uncomfortable psychologically on an unconscious level as we are not expressing our natural boundaries instinct and so we can feel somewhat imbalanced as a result or exploited of being sexually intimate with unfamiliar partners (even while consenting?) I think sexual intimacy is a process and is boundary sensitive and personal values maybe necessary to protect feelings of wellbeing and self esteem so people dont feel negative emotions resulting from sexual interactions with people who havent earned the boundary breaking status.
Oh sorry just saw the PS. Okay, so - many mammals relieving themselves tend to be very much on alert when doing so because they're making themselves very vulnerable. (Just something I heard once, from my brother, so not an expert or anything!) But it makes sense, wouldn't it be horrible if a predator was watching you and waiting for a moment when you're not quite prepared, and they jump on you?
The opposite of cats, dogs seem to want to watch you while they go, and I heard somewhere that's more to do with trust in their pack (their thought process: "hey you're watching out for me right now right?!" whereas cats might be like, "hmmm my brain says I should be alert for anything watching me right now...")
It's interesting you linked shame and shyness, and just as what we 'ought' to be ashamed of is certainly influenced by culture, I am sure there is some cultural influence in terms of what people are shy about. (In the US and the UK, people certainly like to joke about how amazingly 'unshy' older people - male or female - are in the changing room at the gym)
Food for thought...