LENScience 09-501-A3 Growing Up! A resource for Science Classes Growing Up! As a human you are going to spend a life time growing and changing. It all started at the time of fertilisation, or conception, about 9 months before you were born. A single sperm from your father joined with an egg inside your mother s fallopian tube to make a cell called a zygote. The zygote tumbled down the fallopian tube and into the uterus or womb, making copies of itself so it became a ball of cells called an embryo. Inside the uterus the embryo settled into the wall where it could continue to grow and develop. It became a fetus, and kept growing and developing for around nine months until eventually you were born. Resource Sheet 1 Reading Guide But that was just the start. Humans continue to grow and develop from baby to infant, child, teenager and eventually adult. The biggest changes that happen as we grow up are at PUBERTY, when we gradually change from a child into an adult. Once we reach adulthood, we stop growing, but our bodies do continue to change as we grow older. Changing from a child into an adult for a human takes several years. Sperm & egg... Embryo...Fetus...Baby...Child...Adolescent...Adult Puberty is the name given to the physical changes that happen between childhood and adulthood Adolescence is the period of psychological, emotional and social change between puberty and adulthood. Teenagers are also called adolescents. Puberty doesn t happen overnight. You don t look in the mirror one day and SUDDENLY it s happened! It takes several years for a child to change into an adolescent and even longer to fully mature emotionally and become an adult. Girls usually start puberty between the age of 9 and 14. Boys usually start puberty between the age of 11 and 16. The average age for a modern human to reach full emotional maturity is 25! Resource Sheet 2 Science Words Puberty Boys Adolescence Adulthood Puberty Girls Childhood 0 5 10 15 20 25 30 Age (Years) LENScience Healthy Start to Life Growing Up Liggins Institute 2009 Page 24
What happens during puberty? Resource Sheet 3 Compare Contrast Puberty for Boys: Usually starts between 11-16 years old. Hormones are released from the brain The testes grow and start producing the male hormone testosterone Testes start making sperm Pubic and underarm hair grows Facial and sometimes chest hair grows Growth spurt - growing taller and stronger Larger and stronger muscles develop Voice gets deeper because the larynx has grown larger He starts to sweat more His behaviour changes. Puberty for Girls: Usually starts between 9-14 years old. Hormones are released from the brain The ovaries start to mature and make the female hormones oestrogen and progesterone Breasts start to develop Pubic and underarm hair develops Growth spurt - growing taller Eggs start to mature in the ovaries and the girl gets her 1st period She starts to sweat more Her behaviour changes Girls are able to have a child about 2 years after their first period The girls pelvis keeps growing wider for about 4 years after her first period. Puberty is controlled by HORMONES. Hormones are chemical messengers that can control what happens in cells. They can turn switches on and off in the cells to make the different jobs that the cell does start or stop. Pituitary gland In BOYS the FSH goes to the testes What causes puberty to start? FSH Is sent to the sex organs A hormone is sent from the middle of the brain to the pituitary gland. This hormone turns a switch on that makes the pituitary gland produce another hormone called Follicle Stimulating Hormone or FSH. FSH is sent to the sex organs. In GIRLS the FSH goes to the ovaries sperm duct bladder seminal vesicle Fallopian Tube urethra prostrate gland erectile tissue Ovary Uterus penis testis Vagina scrotum The testes release a hormone called testosterone which causes the changes in boys at puberty and is needed to make sperm. The ovaries release two hormones called oestrogen and progesterone which cause the changes we see in girls at puberty. These hormones also control the menstrual cycle. LENScience Healthy Start to Life Growing Up Liggins Institute 2009 Page 25
21 st Century Teens Start Puberty Earlier than their Great Grandparents 21 st century teenagers are going through puberty about 4 years earlier than 19 th century teenagers did. Scientists measure the age of puberty by the time of a girls 1st period. It is harder to measure an exact event in boys - but for both boys and girls - puberty is getting earlier. The graph below shows a study from Europe - but it is happening all over the world. The average age for girls to get their 1st period has got younger over the past 150 years Graph redrawn from Gluckman et al 2009 Originally redrawn from data in Ljung et al (1974) and de Muinich Keizer & Mul (2001) Age at 1st period (years) Year Kiri MacDonald has Māori, Swedish, Scottish and English ancestry. Her great great great grandparents on her father s side of the family, Agnes and Karl Melgren, came from Sweden to New Zealand in 1889. Their daughter Rose married Ian, a young man from Edinburgh in Scotland. On her mother s side of the family Kiri s grandparents are from Ngāti Whātua and London. Kiri got her 1 st period when she was just 10 years old - she was one of the first girls in her class to have her period. Her cousins in Sweden were not so early, they were all 12 when they got their first periods. Kiri s great great great grandmother was probably almost 16 when she got her first period. Why are teenagers starting puberty earlier? Scientists think there are several possible reasons that are contributing to this: One reason is that we have much better living conditions than people did 200, or even 100 years ago. We know that children who have poor health start puberty later. Our lifestyle has also changed over the last 150 years. More people used to live in rural areas, families were not very mobile and most children did not finish high school Today we have clean running water, toilets, sewerage, refrigeration, electric heating and immunisation to protect us from childhood diseases like measles, mumps and polio. LENScience Healthy Start to Life Growing Up Liggins Institute 2009 Page 26
Biological Mismatch Better health and hygiene is not the only reason we are growing up faster. Scientists also think that it has got something to do with the environment that we experienced in the uterus (or womb) - when our mother was pregnant with us. That environment depends on the food that the mother eats every day, as well whether she smokes, drinks alcohol or takes drugs. If what we experience in the first stage of growing up, inside the womb, is different to the environment we experience when we are born, we are more likely to start puberty earlier. This MISMATCH in diet might happen because: - a family migrates from one country to another when a child is growing up - a family shifts from a rural place to a city and there is a big change in diet - our mum s diet when she was pregnant is quite different to what we eat when we are growing up - there could be many reasons why. One special group of children who have helped scientists understand this better are children from intercountry adoptions. Inter-country adoptions involve children, usually from orphaned situations in one country, being adopted by parents who live in another country. In New Zealand there are children from Russia, Romania, Lithuania, India, Philippines and Thailand who are adopted into New Zealand families. Most of these children, for many different reasons were not able to be brought up by their birth parents and were living in orphanages or institutions when they were adopted. The studies that have looked most extensively at inter-country adoption and puberty were in Denmark and Sweden. The children who were adopted were mainly from India. The average age for a girl in rural India to get her 1st period is 14.4 years old. The average age for a girl in a privileged family in India to get her 1 st period is 12.8 years old. In the Swedish study the average age for the adopted Indian girls to get their 1 st period was 11.6 years old. In the Danish study, the adopted girls were 15-20 times more likely to enter puberty early. For Indian girls who shifted to Denmark with their families, the age of puberty did not change. LENScience Healthy Start to Life Growing Up Liggins Institute 2009 Page 27
Growing Up Fast! Student Resource Sheet 21 st Century Teenagers Start Puberty Earlier than their Great Grandparents The average age for girls to get their 1 st period has got younger over the past 150 years Age at 1st period (years) Year Graph redrawn from Gluckman et al 2009 Originally redrawn from data in Ljung et al (1974) and de Muinich Keizer & Mul (2001) Use the information on page 3 of the reading Growing Up to answer these questions. The scientists have plotted the average age that girls get their first period from 1880-2000. Using the information on the graph can you predict the average age for Swedish girls to get their 1 st period in 1875 and in 1925? Puberty is a process that takes several years. Girls start breast development before they get their 1 st period - but the 1st period is easy to put a date on! Boys start puberty about 2 years after girls. Why do you think that scientists tend to report on girls rather than boys when they are studying puberty? Scientists think that one reason why 21 st century teenagers start puberty earlier is because they have better living conditions and are healthier. Make a list of the ways you think living conditions have improved over the past 150 years. Do you think these changes have made us healthier? Make a list of lifestyle changes that have happened in the past 150 years. Do you think these changes have made us healthier? LENScience Healthy Start to Life Growing Up Liggins Institute 2009 Page 28
Advanced Challenge Questions Learning about Puberty from Inter-country Adoptions Inter-country adoptions involve children, usually from orphaned situations in one country, being adopted by parents who live in another country. In New Zealand there are children from Russia, Romania, Lithuania, India, Philippines and Thailand who are adopted into New Zealand families. Most of these children, for many different reasons, were not able to be brought up by their birth parents and were living in orphanages or institutions when they were adopted. The studies that have looked most extensively at inter-country adoption and puberty were in Denmark and Sweden. The children who were adopted were mainly from India. The average age for a girl in rural India to get her 1st period is 14.4 years old. The average age for a girl in a privileged family in India to get her 1 st period is 12.8 years old. In the Swedish study the average age for the adopted Indian girls to get their 1 st period was 11.6 years old. In the Danish study, the adopted girls were 15-20 times more likely to enter puberty early. For Indian girls who shifted to Denmark with their families, the age of puberty did not change. Make a list of the living conditions that you think might be different between what the children had experienced in India (likely to be poverty stricken areas) and the living conditions in Denmark and Sweden. Do you think there would be similar differences in lifestyle for the children of inter-country adoptions in New Zealand? The scientists believe that as well as the changes in living conditions for the children, the age of puberty is influenced by the nutritional environment that the children experienced in the uterus. What do scientists mean when they say nutritional environment? What do you think would be the main differences between the diet of a pregnant woman in rural India and the diet that the girls ate in Denmark or Sweden? LENScience Healthy Start to Life Growing Up Liggins Institute 2009 Page 29
Teenage Mismatch! Does it Matter? One of the biggest challenges for ALL teenagers is that 21st century teenagers are maturing physically before they mature emotionally. For the first time in history, humans are maturing physically much earlier than they are maturing socially. Our biology is not matching the world we live in. In the graph below you can see that 20,000 years ago humans started puberty at about the age of 10. They lived to be 25-30 years old and life was a lot less complicated! You could easily be an adult at age 12. Life is now very complex. It takes us until we are on average 25 years old to reach social and emotional maturity. Scientists are trying to find out more about why this is happening. As teenagers, you need to think about what this MISMATCH means for your generation, and how you can help scientists and the community to understand the challenges of being a teenager in the 21st century. LENScience Healthy Start to Life Growing Up Liggins Institute 2009 Page 30
Teenage Mismatch! Student Resource Sheet Professor Gluckman and Professor Hanson have been studying the development of humans for many years. They are interested in learning about how we can create healthy environments for children to grow up so that they will become healthy adults. They drew the graph on the right to help explain what they have learnt about changes in the timing of puberty and social maturity in humans over the past 20,000 years. What do you think emotional and social maturity is? What was the average age for boys and girls to start puberty 20,000 years ago? How long do you think people lived 20,000 years ago? 20,000 years ago was the time when Homo sapiens shared the earth with Homo neanderthals. They were hunter-gatherers. What sort of food do you think they ate? How do you think our diet today is different to the diet 20,000 years ago? How do you think our diet today is similar to the diet 20,000 years ago? 2,000 years ago humans started to live in small farms, keeping animals to eat and growing crops. What advantages would have come from setting up small farms? The graph shows that 2,000 years ago social maturity was starting to happen later. What would teenagers 2,000 years ago have needed to learn about before they could become independent adults? What major changes happened during the industrial revolution? The scientists have described our diet today as being a nutritional overload. What do you think they mean by this? Imagine you are a science reporter for your local daily newspaper. Write an article for a newspaper about changes in the timing of puberty and social maturity. In your article, report on the scientific findings, but also make some suggestions about what this means for teenagers today. Use the graph as a part of your article. As a reporter, you are going to have the opportunity to interview Professor Gluckman. In your group write 3 questions that you would like to ask Professor Gluckman about the mismatch between the age of puberty and the age of emotional maturity. LENScience Liggins Institute 2009 Worksheets may be photocopied for use in schools http://lens.auckland.ac.nz LENScience Healthy Start to Life Growing Up Liggins Institute 2009 Page 31