What is referred to as hypothetical forms of life that could exist as a transition between species?

The term that describes hypothetical forms of life that could exist as a transition between species is often referred to as a "missing link." This concept encompasses organisms that exhibit traits or characteristics of both ancestral and descendant species, thereby providing evidence for evolutionary transitions. The idea of a missing link highlights the gaps in the fossil record that indicate the gradual process of evolution, particularly in the development of significant features that differentiate one species from another.

By studying these hypothetical transition forms, scientists can better understand the pathways of evolution and the relationships among different species. The notion emphasizes that evolution is not a series of sudden jumps but rather a continuous process, with organisms evolving gradually over time.

Other options, while related to evolutionary biology, do not specifically capture the same meaning as "missing link." Common ancestors refer to species from which two or more species have evolved, transitional fossils are physical remains that provide evidence of evolutionary changes, and gradual forms would imply a continuous spectrum of changes rather than specific forms that may connect two distinct species. Thus, "missing link" is the term that best embodies the idea of hypothetical transitional organisms in the context of evolution.