Final answer:
The statement reflects the biological principle that all life on earth evolved from a common ancestor through natural selection, a process central to the evolutionary theory. This explains the diversity and unity of living organisms, and is supported by the shared characteristics found in the cellular structures of all life forms.
Step-by-step explanation:
The statement 'All life on earth evolved by natural selection from a common ancestor' aligns with the theory of evolution by natural selection as formulated by Charles Darwin. This theory serves as the cornerstone in understanding the diversity and unity of life on Earth, explaining how over millions of years, different species have adapted and evolved from a common ancestor.
Evolution is defined as a change in the characteristics of living organisms over time, which happens via natural selection. Organisms that bear traits providing survival and reproductive advantages are more likely to pass on their genes. This process, coupled with genetic mutations, results in the gradual development of new species. All living organisms, from bacteria to humans, share a common evolutionary history, evidenced by the universal features found in cellular structures.
Scientists use phylogenetic trees to trace the evolutionary relationships and timelines, describing the descent with modification as the pattern by which life diversifies while inheriting characteristics from ancestors. Through this, we see the expansive and intricate web of life that currently exists on our planet.