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.
Heart at Rest. A childâs resting heart rate level depends, in large part, upon her age. For infants, a resting heart rate is expected to be between 100 and 160 beats per minute. In children who are 1 to 10 years old, this resting heart rate should be between 70 and 120 beats per minute.Adolescents and young adults between the ages of 10 and 18 should have a resting heart rate between 60 and 100 beats per minute.o determine your childâs maximum exercise heart rate, you must again consider her age. A childâs maximum exercise heart rate can be calculated by subtracting his age from 220. For example, a 10-year-oldâs maximum exercise heart rate should be 210, while the maximum exercise heart rate for a 16-year-old should be 204.