Final answer:
The concept of LUCA explains that humans, trees, and insects share fundamental biological components due to having evolved from a common ancestor, supported by the universality of genetic material and the genetic code.
Step-by-step explanation:
The common characteristics shared by humans, trees, and insects such as mRNA, the phospholipid bilayer structure, molecular energy systems, and universal genetic code can be explained by the LUCA (Last Universal Common Ancestor) principle. This principle supports the idea that all life on Earth has evolved from a single ancestral cell. The biochemical continuity throughout evolution, as emphasized by Jacques Monod's statement, "What is true for E. coli is also true for the elephant," illustrates the shared biochemistry of life from unicellular organisms to complex multicellular organisms.
Evidence for a common ancestor is reinforced by the universality of DNA as the genetic material and the near universality of the genetic code and machinery for DNA replication and expression. Fundamental divisions between the three domains of life are expressed in structural differences in components like ribosomes and cell membranes. Still, the relatedness of groups of organisms is manifest in the similarity of their DNA sequences, which is what would be expected from descent and diversification from a common ancestor.
Repeated speciation hints at the shared cellular structures, nucleic acids, proteins, and metabolic pathways that date back to our LUCA. Despite differences in physical and reproductive characteristics among life forms, the universal genetic code is nearly so, with only a few minor exceptions. This conservation across diverse species strongly indicates a common origin for all life on Earth.