Survival of the fittest  is a phrase that originated from an evolutionary theory as a way of describing the mechanism of natural selection. The biological concept of fitness is defined as reproductive success.
The normal respiratory rate is 30 to 60 breaths per minute from birth to one year, 24 to 50 breaths per minute from one to three years and 22 to 34 breaths from three to six years old. As the child moves into school-age, the normal respiratory rate slows. From age six to twelve, the normal rate is 18 to 30 breaths per minute, while 12 to 16 breaths is the normal rate from age 12 to 18.
1 Athletes or people on certain medications may have a lower resting normal rate. 2  The normal heart rate for children aged 1 to 8 years is 80 to 100 beats per minute. 3  The normal heart rate for infants age 1 to 12 months is 100 to 120 beats per minute.