Long long time ago a woman, who was about to birth her child would leave her village and seek privacy. Often she would hide in woods close to river shore. There in connection with nature she would become its force in anticipation for meeting her baby.
Just before that woman would leave the village, her mother or sister, maybe friend, which already had experience with birthing children would be notified that baby was ready. The chosen companion would quietly follow, but not interfere unless birthing woman or her baby were in danger. Her job was to be present, close enough, but unseen to protect new mother with her child from wild animals or uninvited guests.
And later when the baby was born and the woman was ready, her quite companion would meet them with open arms and take them back to the village.
That is how old doula work really is.