[Response must be written as a short blurb.]
What is a Clade?

In naturally evolved organisms, the concept of biological cladistics has come to signify the reappraisal of taxonomy using molecular biology and genetic relationships. Although early taxonomists such as Linnaeus and Darwin arranged species, genera, family and orders into family trees according to physical similarities, these trees were subsequently re-arranged due to analysis of the genetic relationships shown by their DNA. Among terragen mammals, for instance, the old taxonomic groupings such as Archonta were replaced by newer biological clades such as the Euarchontoglires, because of evidence of closer relationships on a genetic level.

Cladistics on a sophontological level can't be so precise, because almost all the new forms of sophont that have emerged in the Terragen Sphere since the Interplanetary Age are artificial, and often adopt characteristics that have been copied from other quite different morphologies and mindtypes. It is problematic to construct a family tree for any modosophont in the OA Current Era, because so many factors need to be included. Instead of a tree, sophont cladistics is more like a network, or a matrix.

Characteristics that are included in the development of a new sophont clade, morphology or mindtype may be directly adapted from clades which are commonplace in the locality and period in which they have emerged. On the other hand, characteristics which have been long unused and stored as data may resurface years (or millennia) later, or in a location far from their origin, if they are considered desirable. Other characteristics may be invented de novo from scratch, or developed by observing the characteristics of an alien lifeform on a newly discovered planet, or reconstructed from palaeontological evidence on a long-dead world.

In the current use of the term, a typical sophont clade shares a common template, which often represents the convergence of a large number of different useful physical, informational and psychological characteristics which can work together to produce a viable individual or group of individuals.

Members of a particular sophontological clade generally differ in certain significant respects from other clades, in terms of morphotypic, toposophic, cultural, religio-ideologico-memetic, and phylotoposophic characteristics. On the other hand a significant number of clades have come to resemble one another closely, either by convergent evolution or by deliberate imitation and reverse engineering.

Although clades often share a distinct origin in a particular time and place, it is also usually possible to join a clade by adopting the qualities of that clade using uploading, engeneration, biotechnology or other forms of comprehensive modification. In the Current Era it is commonplace for a modosphont to change their physical form and their psychological and toposophical mindtype in order to adopt a new form, and they can move from one sophontological clade to another with relative ease. However not all citizens of the Terragen Sphere take advantage of this ability, and some clades decline to accept new members or require them to undergo a wide range of requirements, tests, ceremonies or ordeals before they are fully accepted.

Terms
Terragen - Any organism descendant from Earth life.
Uploading - Mind uploading
Engeneration - To transmit one's consciousness into another body
Modosophont - An sophont at a baseline intelligence