Rob Henderson covers some evolutionary arguments on how “we” became who we are today, including some of the ways parents and babies interact:
“Crying Baby” by iamprince160812 is licensed under CC BY 2.0 
.
Intriguingly, some researchers have suggested that infant crying is a signal of vigor that evolved to reduce the withdrawal of parental care.
The idea is that in the ancestral environment, inert, inanimate, lifeless infants were considered by parents to be physically weak or possibly in poor health and thus unlikely to survive. In contrast, being loud and relentlessly fussy demonstrated high energy, strong lungs, and good health. Indeed, infant crying is calorically costly, with a 13% increase in metabolic rate compared to resting.
Exhausted parent: “I’ve tried feeding you, changing you, holding you…What is it that you want?”
Crying baby: “To demonstrate to you how robust I am!”
This is likely why babies will often cry even when there is seemingly no immediate need, such as distress or hunger. Their unconscious, evolutionary aim is to ensure caregivers don’t neglect them or withdraw care or resources from them.
Of course, like most signals individuals send, babies don’t “know” they are doing this.
Infant crying also falls under the framework of error management theory. The idea is that it is more costly to under-react to potential dangers than overreact. In this case, it is better for a baby to be oversensitive and cry even when there is nothing wrong than to be under-reactive and not cry when something is wrong. A variation of this is the smoke detector principle.
A smoke detector produces a piercing, unmistaken alarm in the event of a fire. But it doesn’t actually detect fire — it detects smoke particles and activates upon the merest hint of potential danger. A false positive (e.g., alarm in response to burnt toast) is far more favorable than a false negative (failing to activate in response to flames). Thus these devices are calibrated to be annoyingly over-reactive.
Babies are nature’s little smoke detectors.
