23: Human Growth and Development

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This chapter describes how the human organism grows and develops from fertilization through death. The following stages of life are described in detail: germinal stage, embryonic stage, fetal stage, infancy, childhood, adolescence, and adulthood.

23.1: Case Study: How Our Bodies Change Throughout Life
Instead of using a phone to make a call, this infant is using it for a purpose more suited to his current stage of life — to relieve the pain of teething. While this may look cute, the tendency that infants and young children have of putting objects in their mouths makes them particularly vulnerable to being exposed to toxic substances in their environment that can seriously — and sometimes permanently — damage their health.
23.2: Germinal Stage
This newborn baby is just starting out in life. She has her whole life ahead of her! Actually, that’s not really true. While most of her life is still ahead of her — including life stages of infancy, childhood, adolescence, and adulthood — this newborn baby is not just starting out in life. She’s already nine months old, and what happened to her during those nine months will help shape the rest of her life. Some of the shortest — but most important — life stages occur before birth. These stages
23.3: Embryonic Stage
In many cultures, marriage — along with birth and death — is considered the most pivotal life event. For pioneering developmental biologist Lewis Wolpert, however, these life events are overrated. According to Wolpert, "It is not birth, marriage, or death, but gastrulation, which is truly the most important time in your life." Gastrulation is a major biological event that occurs early in the embryonic stage of human development.
23.4: Fetal Stage
This mother-to-be is holding an ultrasound image of her fetus. She is nearly nine months pregnant, so the fetus is fully developed and almost ready to be born. The fetus has grown tremendously and changed in many other ways since it was a tiny embryo seven months previously.
23.5: Infancy
Infancy refers to the first year of life after birth, and an infant is defined as a human being between birth and the first birthday. The term baby is usually considered synonymous with infant, although it is commonly applied to the young of other animals, as well as humans. Human infants seem weak and helpless at birth, but they are actually born with a surprising range of abilities. Most of their senses are quite well developed, and they can also communicate their needs by crying.
23.6: Childhood
The boys in this photo from 1911 are just children. All of them are between eight and 12 years old — years you no doubt spent in elementary and middle school. For the boys in the picture, those years were spent as coal workers in a Pennsylvania mine. Their job was to separate impurities from coal by hand. For ten hours each day, six days a week, they would sit on wooden seats, perched over chutes and conveyor belts, picking impurities out of the coal. The use of boys to do this work began in the
23.7: Adolescence and Puberty
Adolescence is the period of transition between childhood and adulthood. It is generally considered to start with puberty, during which sexual maturation occurs and adolescents go through a spurt in growth. In many children, however, puberty actually begins during the stage called pre-adolescence, which covers the ages 11 to 12 years. Puberty may begin before adolescence, but it usually continues for several years, well into the adolescent stage, which ends during the late teens.
23.8: Adulthood
This colorful family portrait includes an elderly woman and her young-adult granddaughter from the Hmong ethnic group in Laos. Both grandmother and granddaughter are adults, but they are obviously far apart in age. What ages define the beginning and end of adulthood?
23.9: Case Study Conclusion: Lead Danger and Chapter Summary
These Michigan National Guard Members are on a mission, but they are defending residents from a different type of threat than you might expect — lead in their drinking water. This picture was taken in January 2016 in Flint, Michigan, during what is widely known as the “Flint water crisis.” The crisis started when the city’s water source was switched to a new source that had highly corrosive water. The corrosive water caused lead in pipes to be leached into residents’ drinking water. As you learn

Thumbnail: Eight month-old infant; as a common feature eyes are usually larger compared to the face. Image used with permission (CC BY-SA 4.0; Avsararas).