The spirit doesn't evolve, the personality of the soul does. Humans have a group soul, but have also evolved to have an individual conscious. Animals have only a group soul and reincarnate in groups. The races of humanity are actually personality clusters. Nations and cities also form their own clusters.
Families have group souls.
We are beings of light encased in physical bodies. All thoughts and experiences are recorded in our subconscious minds and in every cell of our body. Our children are not really ours, but God's. They are placed in our care to help them live the life they choose. Our planet has evolved to a point where we are all globally linked and could become one people.