Why would we evolve to feel such grief and loss of will to live when we lose our child? It makes no sense from a biological perspective.
It doesn’t, no animal behaves this way. We’re not evolved to be this way either. In the separated state we form strong attachments to the objects of our love, because we believe they bring us happiness. When we lose them, it is our own long suppressed grief and emotional pain coming up to the surface. When we seek our happiness outside of ourselves, we are bound to be crushed and disappointed sooner or later. It can be very painful.
The loss of will to survive is illusory. Only ego loses its will to survive, the body never does. It’s just an inner desperation from yet another failed attempt to be happy. It’s not dangerous, time heals all wounds, it just needs to be gone through, it needs to be experienced, in a non-judgmental and loving way. Self-compassion is key. Meditation helps, too.
There is no “deeper” reason for loss of a child, things happen. There’s no blame. When we allow ourselves to cry and grieve, we always go through it and emerge on the other side stronger. It’s not biology, it’s psychology.