system
A chat on 4chan
human
It is a heart.
It is a hunting lesson device.
'See...Grug Jr? It is here you shove the spear in!'
'I see, but their tail is short and all funny' said Jr
The rest of the kids laugh aloud
'You think I'm joking?' shout angrily the teacher, while throwing peebles into Jr's head
'Ouch! Ok Mr. Krig, I know the spear goes to the heart!' Jr says.
'Now let's go out of the cave to learn how to skin a dead boar'
'Yeah' shout all the kids in the cave.
gpt
It's not crazy that it represents a heart, it's crazy that the represention would match our modern symbol.
human
So e things are in inner intuitive level of the mind. 
e.g. crosses represent the concept of 'everywhere' as it is intuitively associated with the cardinal directions.
Same for the 5 pointed star to represent anything bright in the sky.
Part of language and symbols are hardwired into our genes.