Little Man is in the unenviable position of having colic and starting teething, which means he is a mega grumpus on a regular basis. Something that has always seemed particularly unreasonable about his behaviour is that he will regularly stop crying and chill out if he is picked up and walked around the house (especially if he goes on his dad’s shoulder, which is good absolute favourite place to be), but the second we sit down with him, he starts crying again.
Up until now, I was under the impression that this was because he is a deeply uncooperative child, but I discovered entirely by accident that THIS IS AN ACTUAL THING THAT ALL BABIES DO BECAUSE OF SABRE TOOTHED TIGERS.
Okay, not sabre toothed tigers specifically, but predators in general. When babies are carried by their caregivers, their heart rate actually drops and they stop voluntary movement and crying. A similar reaction is seen in other mammals. However, this only works if you are carrying them while moving; stationary carrying doesn’t change their behaviour.
It’s proposed that this reaction has the evolutionary function of increasing survival chances if the mother needs to escape from a situation with her child.
Unfortunately for parents with grumpy babies, the soothing effect only works for as long as the baby is being carried around. So if baby is grumpy because he was upset by a loud noise or sudden pain (like immunisations), then carrying them around will soothe them. But if the reason they’re crying is something that’s still ongoing when you try to sit down or put them down (such as hunger or painful wind), they’ll just start crying again straight away. Great.