A phenotypic characteristic, acquired during growth and development, that is not genetically based and therefore cannot be passed on to the next generation for example, the large muscles of a weightlifter. Any heritable characteristic of an organism that improves its ability to survive and reproduce in its environment.
Puberty Upper body of a teenage boy. The structure has changed to resemble an adult form. Puberty is a period of several years in which rapid physical growth and psychological changes occur, culminating in sexual maturity. The average age of onset of puberty is at 11 for girls and 12 for boys. Hormones play an organizational role, priming the body to behave in a certain way once puberty begins,  and an active role, referring to changes in hormones during adolescence that trigger behavioral and physical changes.
It is the stage of life characterized by the appearance and development of secondary sex characteristics for example, a deeper voice and larger adam's apple in boys, and development of breasts and more curved and prominent hips in girls and a strong shift in hormonal balance towards an adult state.
This is triggered by the pituitary glandwhich secretes a surge of hormonal agents into the blood stream, initiating a chain reaction to occur. The male and female gonads are subsequently activated, which puts them into a state of rapid growth and development; the triggered gonads now commence the mass production of the necessary chemicals.
The testes primarily release testosteroneand the ovaries predominantly dispense estrogen. The production of these hormones increases gradually until sexual maturation is met. Some boys may develop gynecomastia due to an imbalance of sex hormonestissue responsiveness or obesity.
The first facial hair to appear tends to grow at the corners of the upper lip, typically between 14 and 17 years of age. This is followed by the appearance of hair on the upper part of the cheeks, and the area under the lower lip.
Facial hair is often present in late adolescence, around ages 17 and 18, but may not appear until significantly later.
Early maturing boys are usually taller and stronger than their friends. Pubescent boys often tend to have a good body image, are more confident, secure, and more independent. However, early puberty is not always positive for boys; early sexual maturation in boys can be accompanied by increased aggressiveness due to the surge of hormones that affect them.
Nearly half of all American high school girls' diets are to lose weight. Girls attain reproductive maturity about four years after the first physical changes of puberty appear.
Adolescence is marked in red at top right.
Growth spurt The adolescent growth spurt is a rapid increase in the individual's height and weight during puberty resulting from the simultaneous release of growth hormones, thyroid hormonesand androgens. The weight gained during adolescence constitutes nearly half of one's adult body weight.
The first places to grow are the extremities—the head, hands and feet—followed by the arms and legs, then the torso and shoulders. During puberty, bones become harder and more brittle.
At the conclusion of puberty, the ends of the long bones close during the process called epiphysis. There can be ethnic differences in these skeletal changes.
For example, in the United States of America, bone density increases significantly more among black than white adolescents, which might account for decreased likelihood of black women developing osteoporosis and having fewer bone fractures there.
This process is different for females and males. Before puberty, there are nearly no sex differences in fat and muscle distribution; during puberty, boys grow muscle much faster than girls, although both sexes experience rapid muscle development.
In contrast, though both sexes experience an increase in body fat, the increase is much more significant for girls. Frequently, the increase in fat for girls happens in their years just before puberty.
The ratio between muscle and fat among post-pubertal boys is around three to one, while for girls it is about five to four. This may help explain sex differences in athletic performance.
These changes lead to increased strength and tolerance for exercise.Course materials, exam information, and professional development opportunities for AP teachers and coordinators. Why is age structure important in the study of human population growth?
Answers Looking at the age structure you can quickly tell whether the population is increasing.
If you were to ask most people to describe female ejaculation, they would probably describe what is most often seen in porn and adult magazines—a gush of fluid from a woman’s vulva at the point of (real or enacted) orgasm.
Oct 19, · With the gradual improvement of health care, the age structure of human population, particularly in developed countries, is skewing toward older people.
This means an ever-increasing percentage of the population consists of those nearing or in heartoftexashop.com: Resolved. In your opinion, why is it significant to think about the age composition of a human population? How does the age composition of a human population affect environmental issues?
Best answer. The human impact on natural ecosystems has reached dangerous levels, even significantly altering the Earth's basic chemical cycles, says a new report, World Resources People and Ecosystems, The Fraying Web of Life. The report paints a dismal picture of over-fished oceans, over-pumping of water for farming, destruction of coral reefs and forests, even too much tourism, with human.