Final answer:
Non-human primates certainly form lineages, as evidenced by their evolutionary history and the common ancestors they share with other species. The phylogenetic tree used to visualize these relationships illustrates how species, including primates, evolve from common ancestors, adapting to different environments over time.
Step-by-step explanation:
Understanding Primate Lineages
The statement 'Non-human primates never form lineages' is incorrect. In biology, a lineage is a sequence of species each of which is considered to have evolved from its predecessor. Therefore, all living organisms, including non-human primates, are part of a lineage. When we look at the evolutionary history of primates, we see that they certainly do form lineages, with each species sharing a common ancestor at some point in the past. For instance, humans and chimpanzees share a common ancestor that lived approximately six million years ago.
A phylogenetic tree is used to represent these relationships among various species, including primates. On such trees, any point where a lineage splits, called a branch point, indicates where a common ancestor gave rise to multiple lineages. The notion that closely related species may have arisen from a single interbreeding species and that the speciation process may not yet be complete is essential to understanding the diversity of life, including that of primates.
Furthermore, it's important to recognize that hominins' lines of descent are complex. Throughout history, more than one hominin species existed at a time, and many of our ancestral species are not directly related to modern humans. Likewise, primates have evolved in various ways, often influenced by geographic changes, which have led to a variety of species with different characteristics, including variability in gender and sexuality.