Theories Contributing to Modern Biology

Modern biology is based on several great ideas, or theories:

• The Cell Theory
• The Theory of Evolution by Natural Selection
• Gene Theory
• Homeostasis

Robert Hooke (1635-1703), one of the first scientists to use a microscope to examine pond water, cork and other things, referred to the cavities he saw in cork as "cells", Latin for chambers. Mattias Schleiden (in 1838) concluded all plant tissues consisted of cells. In 1839, Theodore Schwann came to a similar conclusion for animal tissues. Rudolf Virchow, in 1858, combined the two ideas and added that all cells come from pre-existing cells, formulating the Cell Theory. Thus there is a chain-of-existence extending from your cells back to the earliest cells, over 3.5 billion years ago. The cell theory states that all organisms are composed of one or more cells, and that those cells have arisen from pre-existing cells.

Figure : James Watson (L) and Francis Crick (R), and the model they built of the structure of deoxyribonucleic acid, DNA. While a model may seem a small thing, their development of the DNA model fostered increased understanding of how genes work. Image from the Internet.

In 1953, American scientist James Watson and British scientist Francis Crick developed the model for deoxyribonucleic acid (DNA), a chemical that had (then) recently been deduced to be the physical carrier of inheritance. Crick hypothesized the mechanism for DNA replication and further linked DNA to proteins, an idea since referred to as the central dogma. Information from DNA "language" is converted into RNA (ribonucleic acid) "language" and then to the "language" of proteins. The central dogma explains the influence of heredity (DNA) on the organism (proteins).

Homeostasis is the maintenance of a dynamic range of conditions within which the organism can function. Temperature, pH, and energy are major components of this concept. Thermodynamics is a field of study that covers the laws governing energy transfers, and thus the basis for life on earth. Two major laws are known: the conservation of matter and energy, and entropy. These will be discussed in more detail in a later chapter. The universe is composed of two things: matter (atoms, etc.) and energy.

These first three theories are very accepted by scientists and the general public. The theory of evolution is well accepted by scientists and most of the general public. However, it remains a lightening rod for school boards, politicians, and television preachers. Much of this confusion results from what the theory says and what it does not say.