Evidence of Evolution Writing Assignment

One of Darwin’s most revolutionary ideas was that all living things are related.  According to this theory, all living things found on Earth today are related to each other because all life on Earth shares a common ancestor.  This ancestor, Darwin argued, once lived on Earth sometime in the distant past but is now extinct.  He came to this conclusion, in part, by examining homologous structures.  Homologous structures are things such as limbs (see Figure 1 below) that have a similar structure even though they may have a very different function.

Pig & Elk =  homologous                      Opossum & Armadillo = homologous

Species that share many genetic similarities are considered to be more closely related than two species that have many differences.  The random mutations that occur during DNA replication cause differences in the DNA sequence to build up in independent species over time.  Therefore, the longer it has been since two species separated from an ancestral species, the more time there will have been for mutations to occur in each species.  

Scientists can use an amino acid sequence of proteins to determine the evolutionary history of a group of organisms, because proteins are determined by the DNA base sequence of a specific gene.  One such protein, called hemoglobin subunit alpha, is found in almost all animals and can be used by scientists to determine the degree of relatedness in any group of organisms.  (This protein enables red blood cells to transport oxygen.)  A comparison of the amino acid sequences of several mammals for a part of the hemoglobin protein is provided in Table 2 below. 

Which of the two mammals are the most closely related? How does this support common ancestry?

 Use the evidence provided to support your answer.  State which figure(s) or part of the text you are using for your evidence. Develop a claim, provide evidence,  provide reasoning, including scientific vocabulary, to justify your answer.