What is the evolutionary reason for humans having arms and legs but no tails?

 The evolutionary reason for humans having arms and legs but no tails is primarily due to the shift in locomotion and balance mechanisms as our ancestors adapted to different environments¹²³⁴.

Arms and Legs: The development of arms and legs in humans is tied to our ancestors’ transition from aquatic to terrestrial environments. These limbs helped in movement and manipulation of the environment, which was crucial for survival.

Absence of Tails: Humans, along with other great apes like chimps, gorillas, and orang-utans, do not have tails¹. This is likely due to the shift towards an upright posture and bipedal locomotion¹³. In many animals, tails serve as a counterbalance and aid in movement, especially running¹. However, as humans and their immediate ancestors started walking upright, the tail became less necessary for balance¹³. Moreover, a tail could have been a hindrance to the type of locomotion seen in apes, such as swinging from branch to branch¹.

Interestingly, humans do have a tail during a brief period of embryonic development, which then regresses into the coccyx, or tailbone¹². This is considered a vestigial structure, a remnant of our tailed ancestors². In rare cases, the regression is incomplete, and some people are born with tails².

Recent research has also suggested a genetic factor, identifying a mutation in a gene called TBXT that could be responsible for the loss of tails in humans⁵⁶. This mutation may have occurred randomly in an ape millions of years ago and then passed down to its descendants⁵.

In summary, the absence of tails in humans is a result of evolutionary adaptations related to changes in locomotion and balance mechanisms, potentially influenced by genetic mutations¹²⁵³⁴⁶.