Q26.5-3CC. - Campbell Biology

Question

Suppose a molecular clock dates the divergence of two taxa at 80 million years ago, but new fossil evidence shows that the taxa diverged at least 120 million years ago. Explain how this could happen.

Step-by-Step Solution

Answer

The divergence between the two taxa was different because the gene used for molecular clock analysis evolved slower than the fossils used as evidence of that organism. Due to this reason, the molecular clocks must have represented a different time span than the fossil evidence.

Step1: Evolution

According to the theory of evolution, organisms have been evolving since the world began by the process of natural selection. Evolution can be identified using tools like molecular clocking or using fossils as evidence.

Step 2: Molecular clock divergence

In theory, different levels of molecular variation may be used to determine divergence periods, acting as evolutionary clocks that tick at varying rates. According to the molecular clock hypothesis, DNA and protein sequences develop at a predictable rate throughout a period or across organisms.

Step 3: Fossil evidence

Fossils are crucial evolutionary evidence because they reveal that life on Earth used to be different than it is now. A collection of fossils is studied and placed in chronological and taxonomic order through comparative anatomy, radiometric dating, and DNA analysis.

So, as the molecular clock can be slower than an organism's actual fossil, this can cause the difference between the molecular clock dates and the fossil evidence.