Question

what evidence supports the theory of evolution by common descent?
similar dna sequences among related species show common ancestry.
all organisms have identical dna sequences.
fossils appear randomly in different layers.
species were all created at the same time.

Explanation:

• Similar DNA sequences among related species show common ancestry: This is a key piece of evidence for evolution by common descent. DNA is the genetic material, and similarities in DNA sequences among related species suggest they share a common ancestor. Over time, as species evolve, there are changes in the DNA, but the underlying similarities remain.
• All organisms have identical DNA sequences: This is incorrect. While all organisms use DNA as their genetic material, the sequences are not identical. Different species have different DNA sequences that are adapted to their specific characteristics and environments.
• Fossils appear randomly in different layers: This is wrong. Fossils are found in a particular order in the rock layers. The deeper layers (older) have simpler fossils, and as we move up (younger layers), the fossils become more complex. This order supports the idea of evolution over time.
• Species were all created at the same time: This is not in line with the theory of evolution. The theory of evolution by common descent posits that species have evolved over millions of years through processes like natural selection, and they did not all come into existence simultaneously.

Answer:

Similar DNA sequences among related species show common ancestry.