StoryImage( ‘/Images/Story//Auto-img-117150029014147.jpg’, ‘Illustration courtesy of http://training.seer.cancer.gov‘, ‘Somatic cells reproduce by mitosis, which results in two cells identical to the one parent cell. Interphase is the period between successive cell divisions. It is the longest part of the cell cycle. The successive stages of mitosis are prophase, metaphase, anaphase and telophase. ‘);
StoryImage( ‘/Images/Story//Auto-img-11715007223799.jpg’, ‘Photo by Dr. Robert A. Hedeen’, ‘The invention of the microscope opened up the previously unknown world of the cell.‘);
When the Englishman Robert Hooke invented the first primitive microscope in the late 1700s, a whole new world was opened to biologists. Hooke observed a finely sliced section of cork and noted it was made of individual compartments that resembled the cells occupied by monks in a monastery. He named these compartment cells, and thusly coined the word, cell.
Improvements were made on Hookes primitive apparatus, and by the early 19th century, many scientists were exploring the heretofore unseen world of life. The most famous of these early microscopists was the Dutchman Antoni van Leeuwenhoek. Leeuwenhoek observed living cells and described many of the Wee Beasties, as he called them. In fact, the Dutchman was the first individual to observe human sperm cells.
During the 1800s, many important and fundamental observations were made on cells. The German biologists Schleiden and Schwann, after careful study of various types of tissue, proposed the theory that all living things were made of various types of cells, but they were unable to say where the cells came from.
A bit later in the latter half of the 19th century, the German medical pathologist Rudolph Virchow stated positively that all cells, both animal and plant, came only from pre-existing cells though he was not sure how this came about. Then, about 1880, the process of mitosis was discovered, and the secret of how both plant and animal cells make exact duplicates of themselves was revealed.
Another very important scientist during the late 1880s and early 20th century was August Weismann, who died in 1914. Weismann was an avid supporter of Darwins theory of the evolution of species by means of natural selection. Prior to Darwin, the most widely-accepted theory of evolution was the one embracing the inheritance of acquired characters that was proposed by Jean Baptiste Lamarck in 1810.
Weismann set out to prove Lamarcks theory was nonsense. For 14 generations, he cut the tails off mice and bred them. All of the offspring generated during the 14 generation period were born with tails, while their parents had been tailless.
Weismann said the body of an animal is made of two parts, the body cells or somatoplasm and the reproductive cells or the germplasm. He stressed that hereditary characters were passed on only through the germplasm. He pointed out that the somatoplasm died with each generation, but the germplasm was immortal, it went on forever. This is true.
Did you ever wonder where you came from? Most all of us have known one or more of our grandparents, and a few have known their great grandparents, but that is as far back as it goes. If we consider a human generation to be 25 years, and we look back eight generations or 200 years, we will find that 256 individuals have contributed germplasm to what makes us unique. If we go back 400 years, the number of individuals who have contributed to our genetic makeup is 65,536. The figure becomes astronomical when we go back further than 16 generations.
Another German zoologist during this period was Ernst Haeckel. Haeckels most important contribution was what is called The Biogenetic Law. This important concept states that during the course of the development of an animal, it passes through certain stages that are reminiscent of its past ancestors. This explains why in the development of the human embryo, a tail is present in a postanal position, and there are clefts in the region of the throat that if we were genetically determined to be fish, would have broken through to form gills. In fact, very infrequently the tails are not resorbed before birth, and the human baby is born with a short tail.
Though our body cells may die, our germplasm does not but lives forever if we do our biological duty and reproduce. In this simplistic sense, the physical side of man is truly immortal.
Dr. Robert Hedeen is a former resident of Marylands eastern shore and resided in the Chicago area from 1960 to 1971. He is a retired professor emeritus of biological sciences in the University of Maryland system. He has published more than 30 scientific papers, has written numerous magazine articles, and is the author of two books on the natural history of the Chesapeake Bay.
From the Feb. 14-20, 2007, issue