This post is an improved version of a previous post, which lacked sufficient specificity. I apologize again for the ambiguous wording, as well as for any rules I had violated in posting that question.
The magic system is known as shamanism, and is centered around entering trance states to communicate with spirits and make pacts with them. My world is an animist setting, so things like humans, animals, plants, stones, rivers, and even human dwellings are considered "alive/animate". The ability to practice shamanism is not limited to humans (or Neanderthals for that matter); highly intelligent social mammals such as mammoths, wolves, cave lions, and whales are also capable of using magic.
When a shaman makes a pact, the spirit will always demand some kind of tribute in return for its help. Tribute can be a material offering, an immaterial offering such as prayer, a task to be performed, or simply a favor to be requested later. If the shaman agrees to pay the tribute, the spirit is guaranteed to hold up its end of the bargain. Breaking tribute always results in negative consequences: physical/mental illness, poor hunting, natural disasters, even stillbirths and miscarriages (if a vengeful spirit decides to possess a pregnant woman).
The actual things a shaman can do with their magic are:
- Healing: All illnesses, physical or mental, are caused by damage to one or more of a person's three souls. By guiding a deformed soul back into proper alignment, restoring a stolen soul, or banishing a possessing spirit, the shaman can kick-start the natural healing process.
- Reading omens: Shamans can train to recognize hints left by spirits to signal important events that have already happened, are happening now, or may possibly happen in the future. A shaman can also seek out omens by performing divinatory rituals, such as throwing bones or reading entrails. As the future is not concrete, the shaman can only predict different "futures" that are most likely to happen.
- Elementalism: A shaman can "talk to" the spirit of something in nature to ask it to do something. An example would be asking the spirit of a frozen river to melt the ice, or asking the spirit of a mountain to cause an avalanche. These kinds of spirits have a single, fundamental instinct that can allow shamans to predict how to deal with them. For example, storms are fundamentally destructive, so a storm spirit bound in a pact would likely demand payment that has to do with violence, such as a blood sacrifice. I have a culture that regularly makes effigies of themselves to leave outside during blizzards, so that the blizzard can still destroy something, and thus act according to its basic nature, in exchange for leaving the people alone.
- Animal shapeshifting: To take on an animal's form, a shaman must rhythmically imitate its sounds and/or movements until trance is achieved. The animal's skin may be worn as a cloak to ease the transformation. This ability is commonly used to scout out an unfamiliar area, to send messages over long distances, or to protect one's kinsmen while they migrate through the open wilderness.
- Ancestral evocation: A shaman can lead the spirits of the dead into the physical world from the afterlife and ask for advice, insight, or for access to the spirit's memories. This is frequently used for community-wide recounting of oral history.
- Binding: A shaman can bind a free-moving spirit to a certain place or object. A spirit can explicitly agree to be bound to a place, or the shaman can bind the spirit by trickery or force. A common practical application of this ability is to bind a spirit to a dwelling or camp in order to protect the inhabitants. While bound to an object, a spirit can communicate with anyone who touches the object, whether or not they are a shaman.
An additional note that I forgot to mention in my first post: shamanism has led to the creation of a proto-writing system using different combinations of abstract symbols commonly found in real-world cave art: lines, dots, circles, zigzags, et cetera. These symbols are used by shamans to seal a pact with a spirit as well as bind a spirit, and are used by all people to make tattoos that show group identity and status.
Shamanic power is not an innate, hereditary trait. Theoretically, anyone could become a shaman, if they are willing to endure a dangerous initiation ritual and then train for years to master their abilities.
So, with all these things in mind, how do you think this magic system would affect the development of agriculture (plant and animal) in a Stone Age world?