This study doesn't even make sense. How does crying generate heat? It takes an awful lot of physical movement to generate any measurable about of heat. There's no way they generated enough sonic energy to make a measurable change in temperature.

This is not evidence that the crying act was just to generate heat. Not that it's evidence that they missed their mom, but it's neither evidence for the heat theory.

You can comfort a crying child with a blanket; maybe all human distress is just a need for a blankie?