Which concept suggests that all living organisms share a common ancestor?

The concept that all living organisms share a common ancestor is best represented by descent with modification. This principle, proposed by Charles Darwin, implies that as species evolve over generations, they diverge from common ancestors through various modifications. It emphasizes the idea that different species can trace their lineage back to a shared ancestor and that changes accumulate over time due to natural selection and other evolutionary processes.

Descent with modification encompasses both the gradual changes seen in a species as it adapts to different environments and the branching patterns of evolution that form the tree of life. This concept is foundational to understanding how biodiversity arises through evolution, fostering the idea that the diverse forms of life we see today have origins linked to previous forms.

In contrast, the other choices represent different evolutionary processes or patterns. Adaptive radiation refers to the rapid diversification of a species into various forms to fill different ecological niches. Convergent evolution describes situations where unrelated species develop similar traits due to similar environmental pressures, leading to analogous structures. Parallel evolution involves species that evolve similar traits independently after diverging from a common ancestor, but it does not reflect the deeper ancestral links suggested by descent with modification.