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.
For adults 18 and older, a normal resting heart rate is between 60 and 100 beats per minute (bpm), depending on the personâs physical condition and age. For children ages 6 to 15, the normal resting heart rate is between 70 and 100 bpm, according to the AHA. But a heart rate lower than 60 doesnât necessarily mean you have a medical problem. Active people often have lower heart rates because their heart muscles don't need to work as hard to maintain a steady beat.