1. Universality of DNA and RNA:
* DNA and RNA as the genetic code: All known life forms on Earth use DNA as their genetic material and RNA for protein synthesis. This shared code strongly indicates a common ancestor.
* The Central Dogma: The flow of genetic information from DNA to RNA to protein is consistent across all living organisms, further pointing to a common origin.
2. Similarities in Proteins:
* Amino Acid Sequences: Closely related species have very similar protein sequences. This similarity decreases as the evolutionary distance between species increases.
* Homologous Proteins: Proteins with similar structures and functions found across different species are evidence of common ancestry. For example, the cytochrome c protein, involved in cellular respiration, is found in nearly all living organisms, with variations reflecting evolutionary relationships.
* Pseudogenes: Non-functional genes that are remnants of functional genes in ancestors. These "fossil genes" provide evidence of evolutionary history and changes in gene function over time.
3. Metabolic Pathways:
* Common Metabolic Pathways: Many metabolic pathways are remarkably similar across diverse life forms. This shared machinery points to a common ancestor and indicates that these pathways were established very early in life's history.
* Evolutionary Modifications: Metabolic pathways can be modified and adapted in different lineages, providing evidence for natural selection and adaptation to specific environments.
4. Molecular Clocks:
* Mutation Rates: The accumulation of mutations in DNA sequences happens at a relatively predictable rate. This allows scientists to estimate the time since two species diverged from a common ancestor.
* Dating Evolutionary Events: By comparing molecular sequences, researchers can infer the evolutionary history of different lineages and estimate when major evolutionary events occurred.
5. Horizontal Gene Transfer:
* Exchange of Genetic Material: While not as common as vertical inheritance (parent to offspring), horizontal gene transfer (transfer of genetic material between unrelated organisms) occurs in bacteria and other organisms. This process can introduce new genes and traits, contributing to the evolution of diverse species.
Examples:
* Cytochrome c: The amino acid sequence of cytochrome c in humans and chimpanzees is nearly identical, reflecting their close evolutionary relationship.
* Hemoglobin: Different species have different versions of the hemoglobin protein, which are adapted to their specific environments. For example, high-altitude birds have hemoglobin that binds oxygen more efficiently.
* Antibiotic Resistance: The evolution of antibiotic resistance in bacteria is a prime example of how mutations and natural selection can lead to rapid evolutionary changes in response to environmental pressures.
Important Note: While biochemical evidence is crucial for understanding evolution, it is best considered alongside other fields like paleontology, genetics, and developmental biology for a more complete picture of evolutionary processes.
