School › Growing up › Ages 10–11
The human life cycle
The stages of a human life from before birth to old age, how babies grow, what puberty is and why everyone goes through it at their own pace. With an investigation into how body proportions change as we grow.
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Before birth, a baby develops for about 40 weeks. Scientists divide this into three stages: the germinal stage (weeks 1–2), the embryonic stage (weeks 3–8) and the fetal stage (weeks 9–40).[1]
Babies grow very fast. A newborn's weight typically doubles in six months and triples in one year. Most babies hold up their head at about 6 weeks and sit alone at about 7 months.[1]
Your body proportions change as you grow. In a newborn baby the head is about a quarter of the total length; in an adult it is only about one seventh.[4]
Puberty is when a child's body begins to change as they become an adult. The brain releases hormones that tell the body it is time to change. It is normal for puberty to start any time between about 8 and 14.[2][3]
In puberty, people grow faster (a growth spurt), sweat more, get greasier skin and grow hair in new places such as the armpits. Girls develop breasts and start periods; boys' voices get deeper. Feelings can go up and down, and that is normal too.[2][3][1]
Adolescence (the teenage years) usually lasts from about 12 to 18. Adulthood begins around 20; late adulthood begins in the 60s, when reaction time slows and muscles get weaker.[1]
Try it: Head and body: do proportions change as we grow?
You need
- Tape measures or metre sticks
- A ruler and a set square or a book (to mark the top of the head)
- Pictures of a baby, a child and an adult (the same height on the page)
- The record table and a calculator
Safety
Measuring is voluntary and done in pairs pupils choose; pupils can use only the pictures instead. Do not compare or rank pupils by height. Take shoes off only on a safe, clean floor.
What to do
- Question: is the head a bigger part of the body in babies than in adults? Make a prediction.
- On the pictures, measure the head height (chin to top of the head) and the total height of each person, in mm.
- Divide total height by head height. This tells you how many 'heads tall' each person is.
- Volunteers only: in pairs, measure head height and total height of a volunteer (or your teacher) and work out how many 'heads tall' they are.
- Fair test: measure everyone the same way (standing straight, no shoes, same chin-to-top method) and measure twice.
- Compare: a newborn is about 4 heads tall, an adult about 7. Where do the children in your class fit?
What happens, and why?
In a newborn the head is about a quarter of the total length, so a baby is about 4 'heads' tall. As we grow, the body and legs grow more than the head, so an adult is about 7 'heads' tall. Children are usually in between.[4]
Play: Which life stage?
Each fact belongs to one stage of the human life cycle. Is it before birth, babyhood and childhood, adolescence, or adulthood?
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Quiz
Other ages: Ages 6–7 · Ages 15–16