As defined in Berk's, Development Through the Lifespan, physical development is changes in body size, proportions, appearance, and the functioning of various body systems; brain development; perceptual and motor capacities; and physical health. The physical development of a human being is the unique because of all of the visible changes that every human being goes through. Physical growth results from a continuous and complex interplay between heredity and environment. Humans begin to develop before they are out of their mother's womb. After conception, the zygote is what I consider the earliest development of the human being. The period of the zygote is about two weeks long. The zygote then becomes an embryo. The period of the embryo lasts from the second week on through the eighth week of pregnancy. The embryo then changes to form the fetus. The period of the fetus is from the ninth week until the end of the pregnancy. The zygote, embryo, and fetus all form in the first trimester or pregnancy. By the third trimester, the fetus is around seven and half pounds.

I weighed about eight and one fourth pounds when I was born. My mother still tells me that whe

There are many major puberty changes that take place. In girls, their breasts begin to bud at age ten, and then their height spurt begins. Then their pubic hair appears, followed by the peak of their strength spurt and height spurt. Next their first menstruation occurs. By this time, they have achieved adult stature. By fourteen, girls' breast growth is completed and at fourteen and a half, their pubic hair growth is completed.

Early adulthood is the next part of human physical development. Throughout the twenties and thirties, early adulthood development occurs. During this time, physical changes and the declines in the functioning of the body are so gradual that one can hardly even notice them. When an adult reaches the age thirty, vision starts to decline because the lens stiffens and thickens, and they can no longer see things up close as well. Some of the organs begin to decrease in function as well. When exercising, the respiratory volume decreases and the breathing rate increases with age. The amount of air that can be forced in and out of the lungs decreases up to fifty percent from the age of twenty to the age of fifty. For reasons such as this, athletic performance peaks from the twenties to thirties and then begins to decrease. The research the have done on incredible athletes show us that the upper biological limit of motor capacity is reached by the first part of early adulthood. The declines in heart and lungpower usually show up only during exercise. From the ages of twenty to thirty, the elasticity of the skin begins and continues, and weight gains begin and continue through middle adulthood. Sexual activity increases during this time as well.

Boys major puberty changes occur a little later than girls. First, their testes begin to enlarge at the age of eleven and a half. Pubic hair appears and the penis begins to enlarge at twelve, and then the height spurt begins. Their spermarche occurs at thirteen. At the age of fourteen, they reach the peak of their height spurt, their facial hair begins to grow, and their voice begins to get deeper. After this, the growth of their penis is complete. Then, at fifteen their pubic hair growth is complete and the peak of their strength spurt has occurred. Finally, after all of these changes, adult stature is reached. The most noticeable part of male puberty seems to be the voice as it cracks a lot and the facial hair. For me the most noticeable part of my puberty was the growth of my chest and the arrival of my menstrual cycle. My face seemed to become oilier during this time as well. This was not a fun part of growing up. Once again, as with all the stages of physical development, nutrition and heredity have an impact on puberty, but they mainly only deal with the timing. This age gap is characteristic of the rep

lacement of baby teeth with permanent ones. Writing becomes more legible during this time as well. Organized games with rules begin to become more and more common at this time as well. Puberty is the most distinguishable part of human physical development. After puberty, it seems like there are no more major physical changes that occur. I do not really feel like I have changed that much since I was sixteen. I weigh more, and I seem to be less flexible, but those are both things relative to daily activity.

Over the first year of life, babies begin to organize sounds into complex patterns. During the second half of the first year, babies begin focusing on larger speech units. These larger units are critical to figuring out the meaning of what babies hear. By nine months babies begin to listen to speech for much longer periods of time, and they begin to perceive it on wordlike segments.

The first visible sign of puberty is usually a large growth spurt. A growth spurt is the rapid gain in height and weight. For girls, this growth spurt usually takes place around or after age ten and for boys it usually takes place aroun

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