You’re describing things that are found in many cultures, not things that are found in all cultures. What's the importance of that? If we see the same behavior

You’re describing things that are found in many cultures, not things that are found in all cultures. What's the importance of that? If we see the same behavior show up in many different, unrelated cultures, all across the globe, it would seem to suggest that there is something fairly deep and structural about it. Maybe some cultures can function with something different, but it's not necessarily up for debate, or something that is likely for any one culture, like our own. With regards to anatomy, you can see a similar situation. Some people are born with six digits on their hands, some without certain organs, some with organs of greatly changed size or shape. These exceptions are a part of nature; but great regularity of structure is a part of nature, too. Variation doesn't necessarily indicate "choice" or "arbitrariness".