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A Quarter of One's Life is Spent Growing Up- Part 1

In the previous article, I mentioned that life is a product of love resulting in a combination of new genes. The combination of these new genes is so varied that it helps to diversify each individual's physics and personality. This month, I would like to look at the growth of an individual and the two peaks of growth that are critical for the growth of a human being.

The growth curve of humans has two peaks. Furthermore, it takes about fifteen years to reach full reproductive stage. If we think of a human lifespan as sixty years, it means that we spend about a quarter of our life, to reach this stage. For dogs or cats, it only takes about seven to ten months, which is only about 1/20th or 1/25th of their life. This seems like an awfully long process to me, for humans to be spending a quarter of their life, reaching this stage.

When a child is born, s/he is generally about fifty centimeters in length and grows to be on average, 160 to 170 centimeters as an adult. Of course there are other factors such as nutrition that account for the growth of an individual, but it is mostly decided by the combination of genes from conception. The speed and rate of growth change from the fertilized egg to an adult, varies from person to person.

Two peaks can be observed in the growth of a human being. The first peak is before birth while the fetus is in the womb, and the second is during adolescence. You can imagine how fast the rate of growth is before birth, as the almost microscopic fertilized egg becomes a fetus of about fifty centimeters at the time of birth. This is where the first peak lies.

After birth, the rate of growth suddenly drops and becomes slower. Then, when they reach adolescence, the boys begin a voice change and the girls' breasts begin to develop. This is when the second peak in growth can be seen, and the speed of growth is once again accelerated. Needless to say, the second peak is slower than the first, but children climb up these two peaks to develop into full grown adults.

In Japan, the children are assigned a place in line, depending on their height, with the tallest child in back and the shortest in front. Even if the child is short and stands toward the front of the line while in elementary school, there is a large possibility for her/him to move to the back of the line when reaching junior high or high school. In this case, the second peak was very high for these children. There are large individual differences in the onset of adolescence, which is namely when the sex hormone begins to secrete (note 1) determining the rate of growth. However, the first and second peaks are usually diagrammed in a similar pattern for people of the same race and living conditions.

It is impossible to predict how tall the child will grow as an adult. This is because so many genetic factors (note 2) and environmental influences (note 3) are involved in the determination of height. We are able to somewhat predict that the child will grow tall, if the parents are tall or is raised in a nutritionally rich environment, but too many other factors come into play, and it is extremely hard to make positive predictions.

It is said that when a ballet company admits its students, they try to predict through various growth data until that point, whether the child will grow to be a prima donna. Of course, that is probably why we see so many prima donnas that are quite tall and slender to make a beautiful impression.

They try to predict this height by charting the rate of growth until that point, the height of their parents, and family background. It is even rumored that they take x-rays to examine the bone structure of the auditoners. Even then, it is extremely difficult to predict the growth outcome of the child.


(Note 1) A generic name for estrogen and androgen, etc. indicating the hormones secreted by the reproductive organs to bring about the second phase of growth.

(Note 2) A term generally used when we referred to hereditary genetics.

(Note 3) There are various factors that surround human beings: physical factors such as air and water; natural factors such as sunlight and temperature; biological factors such as viruses and bacteria; cultural factors such as population density, cities, and journalism.

Kobayashi, Noboru (1991). Jinsei no yonbun no ichi wo kakete otonani - 1 (written in Japanese). Tokyo: Child Research Net. Retrieved February 1, 2001, from the World Wide Web:
http://www.crn.or.jp/LIBRARY/KOBY/MIRAI/cbs0075.html
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