Category: 2. History

With Aristotle and Theophrastus, the great Greek period of scientific investigation came to an end. The most famous of the new centres of learning were the library and museum in Alexandria. From 300 BCE until around the time of Christ, all significant biological advances were made by physicians at Alexandria. One of the most outstanding of those individuals was Herophilus, who dissected human bodies and compared their structures with those of other large mammals. He recognized the brain, which he described in detail, as the centre of the nervous system and the seat of intelligence. On the basis of his knowledge, he wrote a general anatomical treatise, a special one on the eyes, and a handbook for midwives.

Erasistratus, a younger contemporary and reputed rival of Herophilus who also worked at the museum in Alexandria, studied the valves of the heart and the circulation of blood. Although he was wrong in supposing that blood flows from the veins into the arteries, he was correct in assuming that small interconnecting vessels exist. He thus suspected (but did not see) the presence of capillaries; he thought, however, that the blood changed into air, or pneuma, when it reached the arteries, to be pumped throughout the body.

Perhaps the last of the ancient biological scientists of note was Galen of Pergamum, a Greek physician who practiced in Rome during the middle of the 2nd century CE. His early years were spent as a surgeon at the gladiatorial arena, which gave him the opportunity to observe details of human anatomy. At that time in Rome, however, it was considered improper to dissect human bodies, and, as a result, a detailed study of human anatomy was not possible. Thus, though Galen’s research on animals was thorough, his knowledge of human anatomy was faulty. Because his work was extensive and clearly written, Galen’s writings, nevertheless, dominated medicine for centuries.

One of the earliest Greek philosophers, Thales of Miletus (c. 7th century BCE), maintained that the universe contained a creative force that he called physis, an early progenitor of the term physics; he also postulated that the world and all living things in it were made from water. Anaximander, a student of Thales, did not accept water as the only substance from which living things were derived; he believed that in addition to water, living things consisted of earth and a gaslike substance called apeiron, which could be divided into hot and cold. Various mixtures of those materials gave rise to the four elements: earth, air, fire, and water. Although he was one of the first to describe Earth as a sphere rather than as a flat plane, Anaximander proposed that life arose spontaneously in mud and that the first animals to emerge had been fishes covered with a spiny skin. The descendants of those fishes eventually left water and moved to dry land, where they gave rise to other animals by transmutation (the conversion of one form into another). Thus, an early evolutionary theory was formulated.

At Crotone in southern Italy, where an important school of natural philosophy was established by Pythagoras about 500 BCE, one of his students, Alcmaeon, investigated animal structure and described the difference between arteries and veins, discovered the optic nerve, and recognized the brain as the seat of the intellect. As a result of his studies of the development of the embryo, Alcmaeon may be considered the founder of embryology.

Although the Greek physician Hippocrates, who established a school of medicine on the Aegean island of Cos around 400 BCE, was not an investigator in the sense of Alcmaeon, he did recognize through observations of patients the complex interrelationships involved in the human body. He also contemplated the influence of environment on human nature and believed that sharply contrasting climates tended to produce a powerful type of inhabitant, whereas even, temperate climates were more conducive to indolence.

Hippocrates and his predecessors were concerned with the central philosophical question of how the cosmos and its inhabitants were created. Although they accepted the physis as the creative force, they differed with regard to the importance of the roles played by earth, air, fire, water, and other elements. Although Anaximenes, for example, who may have been a student of Anaximander, adhered to the then-popular precept that life originated in a mass of mud, he postulated that the actual creative force was to be found in the air and that it was influenced by the heat of the Sun. Members of the Hippocratic school also believed that all living bodies were made up of four humours—blood, black bile, phlegm, and yellow bile—which supposedly originated in the heart, the spleen, the brain, and the liver, respectively. An imbalance of the humours was thought to cause an individual to be sanguine, melancholy, phlegmatic, or choleric. These words persisted in the medical literature for centuries, a testament to the lengthy popularity of the idea of humoral influences. For centuries it was also believed that an imbalance in the humours was the cause of disease, a belief that resulted in the common practice of bloodletting to rid the body of excessive humours.

Although the Babylonians, Assyrians, Egyptians, Chinese, and Indians amassed much biological information, they lived in a world believed to be dominated by unpredictable demons and spirits. Hence, learned individuals in those early cultures directed their studies toward an understanding of the supernatural, rather than the natural, world. Anatomists, for example, dissected animals not to gain an understanding of their structure but to study their organs in order to predict the future. With the emergence of the Greek civilization, however, those mystical attitudes began to change. Around 600 BCE there arose a school of Greek philosophers who believed that every event has a cause and that a particular cause produces a particular effect. That concept, known as causality, had a profound effect on subsequent scientific investigation. Furthermore, those philosophers assumed the existence of a “natural law” that governs the universe and can be comprehended by humans through the use of their powers of observation and deduction. Although they established the science of biology, the greatest contribution the Greeks made to science was the idea of rational thought.

Papyri and artifacts found in tombs and pyramids indicate that the Egyptians also possessed considerable medical knowledge. Their well-preserved mummies demonstrate that they had a thorough understanding of the preservative properties of herbs required for embalming; plant necklaces and bas-reliefs from various sources also reveal that the ancient Egyptians were well aware of the medicinal value of certain plants. An Egyptian compilation known as the Ebers papyrus (c. 1550 BCE) is one of the oldest known medical texts.

In ancient China, three mythical emperors—Fu Xi, Shennong, and Huangdi—whose supposed ruling periods extended from the 29th to the 27th century BCE, were said to possess medical knowledge. According to legend, Shennong described the therapeutic powers of numerous medicinal plants and included descriptions of many important food plants, such as the soybean. The earliest known written record of medicine in China, however, is the Huangdi neijing (The Yellow Emperor’s Classic of Internal Medicine), which dates to the 3rd century BCE. In addition to medicine, the ancient Chinese possessed knowledge of other areas of biology. For example, they not only used the silkworm Bombyx mori to produce silk for commerce but also understood the principle of biological control, employing one type of insect, an entomophagous (insect-eating) ant, to destroy insects that bored into trees.

As early as 2500 BCE the people of northwestern India had a well-developed science of agriculture. The ruins at Mohenjo-daro have yielded seeds of wheat and barley that were cultivated at that time. Millet, dates, melons, and other fruits and vegetables, as well as cotton, were known to the civilization. Plants were not only a source of food, however. A document, believed to date to the 6th century BCE, described the use of about 960 medicinal plants and included information on topics such as anatomy, physiology, pathology, and obstetrics.

Much of the earliest recorded history of biology is derived from Assyrian and Babylonian bas-reliefs showing cultivated plants and from carvings depicting veterinary medicine. Illustrations on certain seals reveal that the Babylonians had learned that the date palm reproduces sexually and that pollen could be taken from the male plant and used to fertilize female plants. Although a precise dating of those early records is lacking, a Babylonian business contract of the Hammurabi period (c. 1800 BCE) mentions the male flower of the date palm as an article of commerce, and descriptions of date harvesting extend back to about 3500 BCE.

Another source of information concerning the extent of biological knowledge of these early peoples was the discovery of several papyri that pertain to medical subjects; one, believed to date to 1600 BCE, contains anatomical descriptions; another (c. 1500 BCE) indicates that the importance of the heart had been recognized. Because those ancient documents, which contained mixtures of fact and superstition, probably summarized then-current knowledge, it may be assumed that some of their contents had been known by earlier generations.

Although it is not known when the study of biology originated, early humans must have had some knowledge of the animals and plants around them. Human survival depended upon the accurate recognition of nonpoisonous food plants and upon an understanding of the habits of dangerous predators. Archaeological records indicate that even before the development of civilization, humans had domesticated virtually all the amenable animals available to them and had developed an agricultural system sufficiently stable and efficient to satisfy the needs of large numbers of people living together in communities. It is clear, therefore, that much of the history of biology predates the time at which humankind began to write and to keep records.

There are moments in the history of all sciences when remarkable progress is made in relatively short periods of time. Such leaps in knowledge result in great part from two factors: one is the presence of a creative mind—a mind sufficiently perceptive and original to discard hitherto accepted ideas and formulate new hypotheses; the second is the technological ability to test the hypotheses by appropriate experiments. The most original and inquiring mind is severely limited without the proper tools to conduct an investigation; conversely, the most-sophisticated technological equipment cannot of itself yield insights into any scientific process.

An example of the relationship between those two factors was the discovery of the cell. For hundreds of years there had been speculation concerning the basic structure of both plants and animals. Not until optical instruments were sufficiently developed to reveal cells, however, was it possible to formulate a general hypothesis, the cell theory, that satisfactorily explained how plants and animals are organized. Similarly, the significance of Gregor Mendel’s studies on the mode of inheritance in the garden pea remained neglected for many years until technological advances made possible the discovery of the chromosomes and the part they play in cell division and heredity.

Moreover, as a result of the relatively recent development of extremely sophisticated instruments, such as the electron microscope, the ultracentrifuge, and automated DNA sequencing machines, biology has moved from being a largely descriptive science—one concerned with entire cells and organisms—to a discipline that increasingly emphasizes the subcellular and molecular aspects of organisms and attempts to equate structure with function at all levels of biological organization.