Question
The universal genetic language of DNA is common to virtually all organisms on Earth, however diverse. What is the best explanation for this fact?- All living things share a common genetic language of DNA because they share a common ancestry.- The universal nature of the genetic language of DNA is due to coincidence.- The universal genetic language is explained by the chemistry of DNA and proteins.
Answer
The best explanation is:
All living things share a common genetic language of DNA because they share a common ancestry.
Why this option is correct
The genetic code is the set of rules that maps three-nucleotide mRNA codons to amino acids or stop signals during translation. Nearly all organisms use the same core mapping. Such a widely conserved and highly specific system is strong evidence that present-day organisms inherited it from a shared ancestral population.
The other choices are weaker explanations:
- Chemistry alone does not require one unique assignment between every codon and amino acid. The shared mapping is therefore not explained simply by the chemical makeup of DNA and proteins.
- Coincidence does not plausibly explain why a detailed coding system is conserved across such diverse forms of life.
Important qualification
Biologists describe the genetic code as nearly universal, not absolutely universal. A small number of codons have different meanings in some mitochondria and microorganisms. Those limited deviations do not erase the much larger shared pattern that supports common ancestry.
Evidence boundary
This answer evaluates the three choices in the cited question version. It explains why the near-universality of the standard genetic code supports common ancestry, but it does not treat that evidence as a stand-alone proof of every evolutionary detail or claim that the code has no exceptions.
Sources
These references support the concepts and methods used in the explanation above.