NSC-103 - Earth Science
Biological Evolution & The History of Life
Terminology & Concepts
Biological Evolution: landmark scientific theory explaining the origin of biological species and the history of life on Earth. It is the foundation of biology (life science) and paleontology (the study of ancient life), and it unifies biological sciences in much the same way plate tectonics unifies the earth sciences. The theory of evolution was co-discovered separately and independently by two men, Charles Darwin and Alfred R. Wallace during the mid-1800s.

Biological classification system (by Linneaus): Kingdom, Phylum, Class, Order, Family, Genus, Species. (Remember: "King Philip Came Over From German Soil")

Population: a group of living organisms which usually consists of members of the same species (closely related enough to interbreed).

Cell: the smallest unit of living matter - it usually contains all the biological machinery necessary to reproduce itself.

Gene: biochemical material in cells which represents a "blueprint" of inherited characteristics passed on to the next generation. The DNA molecule is an example of genetic material.

Fission (Asexual) Reproduction: a type of reproduction involving the simple splitting of "parents" into "offspring" such as that found in bacteria, amoebas, etc.

Sexual Reproduction: reproduction involving the sharing of genetic material by two parents (male and female). Shuffling of the genes and inherited characteristics is much more efficient and evolution proceeds much faster by this method than it does by fission.

Mutation: random errors which occur in the mixing and making of new genes - usually, these mutations cause genetic defects which are harmful; but under unusual environmental circumstances, these mutations may actually be more beneficial than "normal" genes. Examples: sickle cell anemia victims are immune to malaria, while insect survivors of the latest version of pesticides are considered "resistant mutants" who pass on their genes to the next generation.

Genetic diversity: the degree of variation of traits and characteristics in a population. A high degree genetic diversity is the "insurance" policy of a population that may enable at least some members of surviving a drastic or catastrophic environmental change. Much of our medicinal herbs rely on the high genetic diversity of plants from the tropical rain forests - these rain forests are rapidly disappearing.

Biological success: simply put, it measures the ability of a population to reproduce the next generation. Over geologic time, a very successful population eventually spreads geographically and may develop different species over time (example: the dinosaurs, the mammals)

Natural selection: a natural process of "weeding out" the weak, diseased, or otherwise unfit organisms so that only the healthy and strong survive to pass on their genes. "Survival of the fittest" is somewhat of a cliché nowadays; it has been perverted by some unscrupulous people as an excuse to discriminate against ethnic minorities, poor people, or any disliked group.

Ecological niche: a "lifestyle" unique to a particular population of plants or animals; it is nature's way of ensuring that there is enough food and resources to go around.

Adaptive radiation: the spreading of a population over a wide geographical area of different environments over geologic time. As populations become geographically isolated, they may eventually evolve into distinctly different species which can no longer interbreed.

Darwinian Evolution: the small, incremental genetic change (at the cellular level) of a population over geologic time. This theory of slow, gradual change was favored by most biologists and paleontologists, including Darwin himself, who considered himself a geologist by training.

Punctuated Equilibria: a recent theory of evolution proposed by Harvard paleontologist Stephen Jay Gould which stated that the slow, incremental change is occasionally interrupted by fast "leaps" in genetic change which causes new species to be created "suddenly" in terms of geologic time. This theory attempts to explain "gaps" in the fossil record, but it does not contradict Darwin's theory.

Fossil: the remains or traces of ancient life. In general, 10,000 years old is a good cut-off date for classifying something as a fossil.

Paleontology: the branch of geology that specializes in the study of ancient life, chiefly through the excavation, reconstruction, and detailed study of fossils. Paleontologists typically study courses in biology to understand present day life forms as a basis of comparison with fossil life forms, which are often extinct.

The fossil record: the record of the history of life in the earth's rocks. This record is not complete because only a tiny percentage (less than 2%) of everything that lived in the past was ever preserved as fossils. Fossilization is a rare event because a special combination of circumstances over a long period of geologic time is required to preserve traces of ancient life. Most of the fossil record is fairly recent, going back 600 million years (when creatures with hard skeletons evolved); before that, (up to 3.2 billion years ago) the fossil record is very scarce. Examination of the fossil record was a foundation for the theory of  evolution. The general trend of the fossil record is an overall increase in complexity of life through geologic time.

Preservational bias: the "unequal representation" of the fossil record, due to differences in the way different animals and plants became fossilized (or not fossilized). Large animals, those with bones or hard parts, and sea creatures tend to be preserved well as fossils. Insects, by volume, are the most numerous members of the animal kingdom today; but because insects don't have bones or hard parts, they make very poor candidates for fossils. Fossil hunters of the distant future would never figure out how numerous insects were because they weren't preserved.


  1. Creature or plant is one or more of the following: a member of a large, widespread population,; possess a skeleton or hard parts, lives in or near water.

  3. Creature dies in or near still, quiet water (protects the corpse from most scavengers and decay). Quiet water has a lower oxygen content and prevents microbe decay.

  5. After death, immediately burial by sediment further protects the skeleton.

  7. Burial of the sediment under new sediment over geologic time eventually produces sedimentary rock.

  9. Over geologic time, gradual uplift of the rock layers without deformation or metamorphism of the rocks exposes the fossils.
Extinction: the complete disappearance of a species, usually due to some environmental crisis to which that population could not adapt successfully. Extinction is the eventual fate of all living things - it has been going on since life began on earth.

Principle of Faunal Succession: from the fossil record, there is an overall increase in complexity from older rocks to younger rocks; once extinct, those species never reappear again later in the fossil record.

Mass extinction: the wholesale death of many species throughout the world within a short period of geologic time. Mass extinction has been documented in the fossil record many times during the geologic past (John Sepkoski and David Raup of the University of Chicago believe that there is a 26 million year cycle to these mass extinctions.); The disappearance of the dinosaurs at the end of the Cretaceous Period (65 million years ago) is the most dramatic example of a mass extinction. Mass extinctions are usually, but not always, caused by a drastic change in the environment, such as a period of intense volcanism, a
climatic change (such as an ice age), or the crash-landing of a giant meteorite.

Ecosystem: the sum total of the interactions between the physical environment of a particular area and its biological inhabitants.

Ecological vacuum: a biological void left in the world ecosystem caused by a mass extinction of many species. The death of the dinosaurs left the post-Cretaceous Earth ripe for the mammals to take over - this would not have happened had the dinosaurs lived.

Human evolution: homo sapiens sapiens (modern man) is the product of nearly 4 million years of evolution of hominoid primates. There is an erroneous popular belief that man evolved from apes; this is not true. Modern apes (gorillas, chimpanzees, orangutans) and humans evolved from a common early ancestor as different from apes as it was from humans; so modern apes are "very distant biological cousins" and not our ancestors. The fossil record of humans is the most scarce because humans have not been around very long, geologically speaking.

Scopes “Monkey Trial”: Evolution was a radical idea when first proposed; during the 1860's, Charles Darwin bore the brunt of organized opposition, but eventually scientists found overwhelming evidence in support of evolution and established it as a landmark theory and foundation of modern biology and paleontology. The most controversial concept was that humans were subject to evolution as were all other animals. In 1925, biology teacher John Scopes was arrested for violating a state law that prohibited the teaching evolution to his students in Dayton, Tennessee. The “Monkey Trial” was an international event and one of the first to be broadcast over radio. Defending Scopes was celebrated trial lawyer Clarence Darrow from Chicago. Acting as state prosecutor was William Jennings Bryan, a three time presidential candidate who was active in the religious revival movement. Although Scopes was later convicted, during the trial, Darrow subjected Bryan to a humiliating cross-examination that revealed Bryan’s ignorance of basic scientific principles. The world-wide press coverage also heaped ridicule upon the town and state that convicted Scopes.

Social Darwinism: Unfortunately, many decades ago, the phrase “survival of the fittest” was corrupted by unscrupulous politicians to justify policies of discrimination, unequal treatment, and mistreatment of certain groups of people (including ethnic minorities, the poor, religious sects, or any disliked group chosen as scapegoats). During the 1920's, Social Darwinism even gave rise to a pseudo-scientific form of racism where skull and brain case measurements were used to “prove” the superiority of one race over another.

Creationism: During recent decades, a reactionary political movement that sought to ban the teaching of evolution in public schools advocated the teaching of “creationism” as a viable scientific alternative. Unfortunately, creationism (or “creation science” as some followers call it) is pseudo-science, and is largely based upon a re-hash of long discredited ideas similar to catastrophism of the early 1800's. Supernatural events are usually invoked to explain the Earth’s creation, earth history, and the history of life. Creationism’s attacks upon evolution are usually based upon out-of-context quoting of arguments between paleontologists, combined with spurious interpretations of physics (ignoring that the earth is not a closed system invalidates application of the Second Law of Thermodynamics, which states that in a closed system, all matter and energy tend toward greater randomness rather than greater order or complexity). No serious, refereed scientific journal ever publishes creationist articles because creationism violates the basic principles of science, which requires constant testing and modification of ideas based upon all available (pro & con) evidence. Instead, creationism uses only one preconceived explanation (biblical Genesis) and rejects or ignores any contradictory evidence. To accept what creationism advocates as serious science would be akin to substituting the Flat Earth theory for plate tectonics in the earth sciences. A federal judge declared in the 1982 Arkansas court case that “creationism is thinly disguised religion, not science.” Most mainstream religions and most scientists find no conflict between science and religion, so long as they are not confused with each other. Science focuses on explaining “how” things work and is not in the business of explaining “why” or “for what purpose” regarding the universe - these are questions perhaps better answered by religion and faith.

Copyright © 1989 by William K. Tong