Similar to life in the ocean, life on the land has gone through a succession of larger ecological forms. The first of these five stages was described in the last chapter. The next three are described in this chapter. The stage we are in today will be looked at in the following chapters. A diagram is presented that shows all five stages. These stages are defined by assemblages of plants as much as kinds of animals. Bruce Tiffney laid out the five stages of plants, going from the liverworts and mosses of the first stage, through horse tails and clubmosses, then ferns, then cycads and conifers. Finally, the angiosperms make up the stage that we are in today, though plants from all the other stages are still present. All these stages can be looked at as cooperative extensions of the soil community.
Even the seed, first developed by the gymnosperms of stage 4, shows a remarkable variety of ways that it measures its own environment and makes decisions about when to sprout. Plant intelligence and decision-making are generated by an interactome, similar in structure to the complex of chemical pathways in both the prokaryotic and eukaryotic cells. The large scale structure of this decision-making in plants results from undifferentiated stem cells located in three places: at the tip of each branch, at the tip of each root and in the cambium in the stem or trunk of the plant. This last layer of stem cells is where the interacting demands for nutrients from the branch tips, and sugars from the root tips are mediated. The whole plant can be seen as a brain. A wide array of chemical, electrical and hydraulic signals transmit the conversation through which a plant makes new leaves and branches and looks for particular nutrients with its roots. Plants are also now being shown to communicate with each other and with their insect partners. They send chemical and even sonic signals through the air, and through the fungal network in the soil. Large classes of chemicals like terpenes are used for both communication and defense. Research has provided many clues, but larger questions about the degree of this connection are still unanswered.
The animals of the second, third and fourth stages on the land developed from the arthropods of the first stage, as they developed into millipedes and insects like the dragonfly. During the second stage another animal emerged from the ocean: the first footed fish, which evolved into the proto-amphibians, with predators like eryops. The true reptiles of the third stage branched into both plant eaters and carnivores.
The increasing complexity of these stages can be understood as cooperative wholes. These wholes can be seen in the trophic pyramid diagram, with carnivorous reptiles on top, going down through other reptiles, then insects and then plants, down to the soil community. Each level of predation formed negative feedback loops of control that helped to stabilize the larger entity of the ecosystem.
Successive stages can be seen as being more intelligent in the ways that they regulated themselves. The dinosaurs of stage four were different from the previous reptiles in several ways, but most important was their increased intelligence. This allowed them to hunt and to defend themselves in cooperative groups packs and herds. It also allowed mothers to rear their young. This created childhood: a time in the individual life when the parent can pass along cultural knowledge about the environment: food sources, dangers, migration routes and so on. This can be seen as a new and more responsive form of evolution, beyond the genetic and epigenetic forms that were already in process.
The major extinction episodes are looked at briefly to distinguish which of them were externally caused, like asteroid impact, and which of them were caused by life itself, like glaciation and oxygen depletion. The external extinctions are seen mostly not to have had causal impact on the development of life.