Given below are two statements.

Statement I : Branching descent and natural selection are the two key concepts of the Darwinian theory of evolution.
Statement II : Lamarck believed in the concepts of the use and disuse of organs, as well as the inheritance of acquired characteristics. 

In light of the above statements, choose the correct answer from the options given below.

Statement I:
"Branching descent and natural selection are the two key concepts of the Darwinian theory of evolution."

This statement is true. Charles Darwin's theory of evolution is primarily based on two key concepts:
Branching descent (also known as common descent) refers to the idea that all species are related through common ancestors and have diverged into different species over time.
Natural selection is the mechanism by which organisms with traits better suited to their environment are more likely to survive and reproduce, passing on those beneficial traits to their offspring.
Statement II:
"Lamarck believed in the concepts of the use and disuse of organs, as well as the inheritance of acquired characteristics."

This statement is also true. Jean-Baptiste Lamarck proposed that organisms could change during their lifetime through the use or disuse of certain organs, and these changes could then be inherited by their offspring. For example, Lamarck suggested that giraffes' long necks evolved because their ancestors stretched their necks to reach higher leaves, and this acquired trait was passed down to future generations.