Question

Read the following passage and answer the questions that follow.

The most convincing evidence to trace evolutionary relationships between humans and different groups of animals come from the basic similarities seen at the molecular level. Study the table given below that depicts the number of amino acid differences between the haemoglobin polypeptide of a few animals with that of humans and answer the questions that follow.

S.No.	Animal	No. of amino acid differences in haemoglobin with that of humans
1.	Macaque	08
2.	Dog	32
3.	Bird	45
4.	Frog	67
5.	Lamprey	125

(a) To which category of evolution (Divergent or Convergent) do the following evolutionary relationships belong to:

(i) Humans and Macaque

(ii) Humans and Frog

(b) What do the biochemical similarities in haemoglobin suggest about the evolutionary relationship between humans, frog, and lamprey?

(c) (i) Which one of the two – lampreys’ or macaques’ evolution is more closely related to humans and why?

OR

(c) (ii) Which one of the two – frogs’ or dogs’ evolution is more closely related to humans and why?

Hint:

Fewer amino acid differences in homologous proteins such as haemoglobin suggest closer evolutionary relationships. Molecular evidence often provides the most reliable data for constructing phylogenetic trees.

Answer 1

(a)

• [(i)] Humans and Macaque: Divergent evolution – both share a common ancestor and have evolved differently.
• [(ii)] Humans and Frog: Divergent evolution – indicates a common ancestry but more distantly related due to higher differences.

(b) Biochemical similarities (fewer amino acid differences) indicate a closer evolutionary relationship. Hence, humans are more closely related to frogs than to lampreys, and even more closely related to macaques. (c)

• [(i)] Macaques’ evolution is more closely related to humans because they have only 8 amino acid differences, whereas lampreys have 125 differences.
• [(ii)] Dogs’ evolution is more closely related to humans than frogs because dogs have 32 amino acid differences, while frogs have 67 differences.