Question 22M.1.SL.TZ1.20
| Date | May 2022 | Marks available | [Maximum mark: 1] | Reference code | 22M.1.SL.TZ1.20 |
| Level | SL | Paper | 1 | Time zone | TZ1 |
| Command term | Question number | 20 | Adapted from | N/A |
Mammals, birds and reptiles have an embryonic tail that may disappear during development.
What is the most likely explanation?
A. Mammals have lost their tail by evolution.
B. All vertebrates have a common ancestor.
C. Mammals, birds and reptiles are identical when they are embryos.
D. Some physical similarities of vertebrates are analogous.
[1]
B
The expected explanation of the presence of tails in vertebrate embryos and subsequent disappearance during development in some species was that vertebrates have a common ancestor which had a tail. All the other possible answers were incorrect — not all mammals are tailless, vertebrate embryos are not all identical, and physical similarities in vertebrates are more likely to be homologous than analogous. Nearly half of candidates answered the question correctly and the discrimination index for this question was relatively high.
