Question

---------is useless in human but is useful and fully functional organ in ruminants.

Tail bone

Wisdom teeth

Appendix 

Body hairs


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Answer 1

Appendix is the answer .
It’s present in the digestive system of both ruminants and humans

Answer 2

Answer:

The appendix is useless in humans but is a useful and fully functional organ in ruminants.

Explanation:

Organs that are functional in ancestors but in the present forms are functionless and occur in degenerated conditions are known as vestigial organs.  

• For example, the wings of flightless birds, rudimentary eyes of cave-dwelling animals, and splint bone in the leg of a horse.

• Man has many vestigial structures such as a nictitating membrane in the eye, vermiform appendix at the end of the caecum, coccyx or tail vertebrae, nonfunctional muscles of the pinna and a lot more.

• All such organs are useless to their possessors but their presence can be explained only by assuming their inheritance from ancestors where these organs were previously functional.

• Man who is terrestrial and bipedal needs no tail but he has evolved from arboreal monkey-like ancestors through semiarboreal apes.

• Monkeys possess a functional tail and apes and man possess only their vestiges (coccyx bone).

• Hence, the vestigial organs prove that the present-day forms have evolved from dissimilar ancestors.  

• Vestigial organs in the ruminants of features that serve important functions in the organism's ancestors.

• The vermiform appendix is a functionless organ in humans but in herbivorous mammals like cows, it helps in digesting cellulose.

Thus, the correct and most appropriate answer is Appendix.

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