Question

Which of the following is not atavistic in humans?
A) Tail in some babies
B) Enlarged canine
C) Six fingers
D) Dense body hair

Answer 1

The reoccurrence of certain traits is known as atavism. It is not associated with diseases related to phalanges. Atavisms have been observed in humans, such as in infants.

Step by step answer: Atavism is the reappearance of certain ancestral structures that have either completely disappeared or greatly reduced. The remote ancestor’s characteristics are seen that disappeared first and then are still seen, like tail in some babies and dense body hair or also enlarged canine. Sometimes the genes that have disappeared through evolution are not fully removed from the body. The genes responsible for such traits are still passed on to the organisms and are expressed in some people. It also depends on the phenotype of the person that was present in the genome of the parents but was not expressed. Such unused genes can remain inactive in the genome of the species for longer generations. This reappearance of genes after several generations can be triggered by a stimulus like generation gap, homologous pairing or adaptation changes, etc. is called atavism or reversal. The examples are;
i. Infants with a tail which is vestigial.
ii. Large teeth or enlarged canines.
iii. Reappearance of limbless animals in limbless vertebrates.
iv. Extra toes in the guinea pig.
v. Dense body hair
vi. Colour blindness in humans
Hence, the correct answer is option C.

Note: The atavism and vestigial organs are different and cannot be the same. These 'useless' body-parts, otherwise known as vestigial organs, are remnants of lost functions that our ancestors possessed. Examples of vestigial organs include an appendix, pelvic bone of a snake, etc.