This idea explains the mechanisms of genetic inheritance and describes the environmental and genetic causes of gene mutation and the alteration of gene expression.
The fourth core idea, LS4: Biological Evolution: Unity and Diversity, explores “changes in the traits of populations of organisms over time”  and the factors that account for species’ unity and diversity alike.
Life scientists use observations, experiments, hypotheses, tests, models, theory, and technology to explore how life works.
The study of life ranges over scales from single molecules, through organisms and ecosystems, to the entire biosphere, that is all life on Earth.
Finally, the core ideas in the life sciences culminate with the principle that evolution can explain how the diversity that is observed within species has led to the diversity of life across species through a process of descent with adaptive modification.
The committee developed four core ideas reflecting unifying principles in life sciences.
These core ideas are essential for a conceptual understanding of the life sciences and will enable students to make sense of emerging research findings.
The role of unifying principles in advancing modern life sciences is articulated in The Role of Theory in Advancing 21st-Century Biology and A New Biology for the 21st Century [2, 3].
In developing these core ideas, the committee also drew on the established K-12 science education literature, including National Science Education Standards and Benchmarks for Science Literacy [4, 5].