Modern science tells us that the conscious self arises from a purely physical brain. We do not have immaterial souls.
Imagination is Reality Lite - a useful substitute when the real pleasure is inaccessible, too risky, or too much work.
Families survive the Terrible Twos because toddlers aren't strong enough to kill with their hands and aren't capable of using lethal weapons. A 2-year-old with the physical capacities of an adult would be terrifying.
We know that young babies, as they become capable of moving voluntarily, will share. They will share food, for instance, with their siblings and with kids that are around. They will sooth. If they see somebody else in pain, even the youngest of toddlers will try to reach out and pat the person.
We benefit, intellectually and personally, from the interplay between different selves, from the balance between long-term contemplation and short-term impulse. We should be wary about tipping the scales too far. The community of selves shouldn't be a democracy, but it shouldn't be a dictatorship, either.
On many issues, empathy can pull us in the wrong direction. The outrage that comes from adopting the perspective of a victim can drive an appetite for retribution.
