These are definitions for words that I've used in my other web pages.

± ("Plus or Minus"): Standard Error In Measurement

A scientist who reports a measurement is also supposed to say how accurate the number is. There are rules for calculating the standard error value. On a graph, this often referred to as an error bar, because a value is drawn as a bar instead of as a point.

For example, one historical measurement of the speed of light was 303,000 ± 6000 kilometers per second ("km/s"), whereas one recent measurement was 299,792.4586 ± 0.0003 km/s. So, the newer measurement technique is approximately 20 million times more precise. But we still need to know the standard error of the newer measurement. Measurements are never infinitely precise.

Notice that the new value falls inside the standard error of the old value. The old and the new differ by about 3200 km/s, which is nicely less than 6000 km/s. This means that the two results are compatible. If they weren't compatible, we would want an explanation.

If you have studied statistics, you will realize that the main value says where to draw the center of a bell curve. The standard error is basically giving the width of that bell curve. The "true value" should be somewhere under the curve.


When one species transforms into another across time.

Arms Race

In politics, an arms race is when two countries both improve their military power, each trying to get ahead of the other.

In evolution, the phrase is used to describe two creatures co-evolving to keep up with each other. For example, gazelles are now very good at running away from cheetahs. But cheetahs are now very good at running after gazelles.


Biochemistry is the branch of chemistry that deals with the the chemicals and chemical processes found in living things.

So, although it is partly in the world of biology, it is also connected to chemistry and medicine.


In a cell with a nucleus, most of the the genes (genetic information) are stored on structures called chromosomes. For example, each cell in a human has 46 chromosomes. We are diploid, so we actually have 23 pairs of chromosomes.


When one species branches into two species across time.


A substance which makes some chemical reaction happen faster, but is not itself consumed in the reaction.


See biological classification


Modern bacteria reproduce by splitting in two - that is, they have asexual reproduction. But a bacteria can join temporarily with another bacteria to swap genetic fragments. This conjugation process is why so many bacteria have recently become antibiotic resistant. The process permits bacteria to form a sort of community.


A diploid cell is one that has two copies of its genetic information. Each copy is from a different parent. All of the cells in your body (except sperm or egg cells) are diploid.


De-oxy-ribo-Nucleic Acid. The chemical that all life uses for long-term storage of genetic information. Your genes are made of DNA. A chromosome contains one enormously long DNA molecule.

A DNA molecule is often diagrammed as a spiral ladder. This diagram ignores many details, to the point where it's pretty much a cartoon. It does capture the crucial fact that the cross-arms are made of the bases Adenine,Cytosine, Guanine, and Thymine (A,C,G,and T). Specifically, there are four possible cross-arms: AT, TA, GC and CG.


The French word for getting a pie in the face.


An enzyme is a protein which is a catalyst for some chemical reaction.


A eukaryote is a cell with a nucleus. (As opposed to a prokaryote, which is a cell without a nucleus.) Plants and animals are made up of eukaryotes.

A eukaryote might be 25 microns across, and a nucleus is about 5 microns across. So, one cubic inch of flesh might hold a billion eukaryotes. An adult human has about a trillion eukaryotes.

An E. coli bacteria is a prokaryote and is about one micron across. So, about 10,000 E. coli would fit inside one eukaryote. About a thousand viruses could fit inside one E. coli.


See Brief definitions


This word is most commonly used by Creationists. People who study (or espouse) Evolution don't mind being called this. However, Evolution is about life forms. Many Creationists seem to apply this word to any branch of science that thinks the earth is old. Geology, physics and astronomy are often described this way, although none of these sciences care one way or the other about Darwin's theories. Scientists in those disciplines find it quite odd to be called Evolutionists. In fact, the old age of the earth was originally established (in the early 1800's) by scientists who were all Creationists.


See biological classification


A gene is the basic unit of hereditary information. It is made of DNA. In a cell which has a nucleus (a eukaryote), each gene in the nucleus is at one specific place (locus) on one of the chromosomes.

A eukaryote also has some genes in small bodies called mitochondria.


Your genome is just the complete set of your genes.

More precisely, it's your haploid set. (You acquire one genome from your mother, and one from your father.)


The genetic makeup of a specific individual. This, plus the environment they grow up in, determines phenotype.

If we are discussing some trait (some particular aspect of the phenotype), then the word genotype refers to just the relevant genetics, not the whole genome.

Genus, Genera

See biological classification


A haploid cell is one that has a single copy of its genetic information. For example, sperm and egg cells are haploid.


Sol is the Sun. So, insolation is just the total amount of sunlight which is received across a period of time.


An inversion is a mutation that literally flips a segment of a chromosome. It is as if the segment was removed, turned by 180 degrees, and then re-attached.

Irreducible Complexity

Behe's name for the idea of a system which would stop working if any of its components was removed. Such systems evolve quite often.


Not all atoms of (say) gold have the same weight. Some gold atoms contain more neutrons than "usual", and some contain less. They're all gold, chemically, because the chemical properties are controlled by the outer electrons, and a neutron 'way down in the nucleus has no effect on electrons.

Some isotopes aren't stable, and the nucleus can come apart. We call that isotope radioactive. For example Carbon 14 is radioactive, but Carbon 12 isn't. Uranium 235 is very radioactive, but Uranium 238 is only mildly radioactive.

If two isotopes of one element are mixed together, it is very difficult to separate them. No chemical method works, because both isotopes have identical chemistry. Usually we use centrifuges, or else distillation. Distillation works because lighter molecules are a little quicker to evaporate.


See biological classification

Light Year

One light year is the distance that light travels in one year.

The speed of light is about 300,000 kilometers per second, or in English units, 186,000 miles per second. So, a light year is about 1013 kilometers, or 6 trillion miles.


This means evolution at the level of a species, or higher. For example, the evolution of land animals into whales would be macroevolution. A species of moth turning black is microevolution (change within a species). A new species arising (speciation) is therefore macroevolution.

Many Creationists say that their argument is with macroevolution, and not microevolution. Most scientists consider macroevolution to just be microevolution which has gone on for a long time. However, some scientists argue that the distinction between macro- and micro- is useful.


This means evolutionary change within a species. See macroevolution for the difference between these two ideas.


A micron is one micro-meter.

So, a thousand microns is a millimeter, and 25,400 microns is an inch. The diameter of an atom is less than a nanometer, so a row of atoms one micron long would have several thousand atoms.


Morph in general just means "form".

So, a creature's morphology is its body shape. And, looking at a fossil gives you morphological evidence, as opposed to evidence about genetics, or about behavior.


A mutation is any genetic change which is due to malfunction. The genetic machinery is highly reliable, but it is not perfectly reliable. There are many different kinds of misteak that can occur when genetic information is copied.

An albino is an example of a person with a mutation. However, many birth defects are not examples of mutation.

Neutral Drift

A neutral mutation is one that does not give an advantage or a disadvantage to the individual possessing the mutation. It doesn't change his or her probability of leaving descendants. Most mutations fall in this category.

Neutral drift is the idea that a neutral mutation can spread throughout a population, so that eventually everyone inherits it. There is nothing specific to cause this, but then again, nothing specific prevents it either. The chance of it happening is low if the population is large. but the chance is high if the population has very few individuals.


The scientific study of fossils, and all aspects of extinct life.


The observable properties of an individual - how big they are, and so on. This is the result of both the environment they grew up in, and their genotype.


The "family tree" diagram showing the possible relatedness of a group of species.

Alternatively, the evolutionary history of a group of species.

Phylum, Phyla

See biological classification


A protein is a molecule which is a long chain (a polymer) of amino acids. The chain may be coiled up, but some proteins are shaped more like ribbons or sheets.

(A few proteins, like hemoglobin, are actually several chains. And there are some stranger cases.)

Rube Goldberg

Rube Goldberg was a popular cartoonist. He drew silly machines that worked in the most roundabout way possible. In Britain, similar humor was done by Heath Robinson.

Imagine a ball which drops, causing sandpaper to light a match, which fires a cannon, which wakes up a monkey, who starts a circular saw, which cuts through a telephone pole, which then falls on the villain. That sort of thing.

In America, if you say that a design is Rube Goldberg, you are insulting it. You are saying that a good engineer would have used a much better design.


A leap. It was once thought that evolution proceeded by occasional large jumps, rather than by smooth gradation from generation to generation.

We now have examples of both, and there is occasional debate about how often saltation happens. Note that we are not talking about a dog turning into a cat. A saltation is more on the order of one extra pair of ribs.


A sequence is just a description of the bases that were found along a stretch of DNA. We write a sequence down as a string of letters, where each letter is either A, T, G or C. (The name of the movie GATTACA was chosen because it is a sequence.)

Sexual Reproduction

In biology, this is just the idea that a child gets its genetic material from each of two parents.

We're used to the idea that one parent is "male" and one is "female", and that the two kinds of parent look different. But that's not actually required. With snails, and with trees, one individual can simultaneously be both male and female. So, a species with sexual reproduction may or may not have sexes.

Sexual Selection

This is what is happening if an individual chooses a mate from a set of potential mates.

For example, there are several kinds of birds where the males have enormous tail feathers. It has been proven (by experiment) that the females prefer the male with the largest tail. So, each of these species would have slowly acquired larger and larger tails because of sexual selection.


That's actually a deep subject, but the short answer is: a species is a set of creatures which, in their natural setting, breed among themselves.


See Brief definitions


A mutation that moves a portion of a chromosome to a new location, generally on a different chromosome.


When a piece of DNA moves from one place in a genome to another place, that is called a transposition. The name "transposon" is short for transposable element.

Like a normal gene, a transposon specifies how to make a particular protein. In this case, the resulting protein can cut and paste DNA. It snips out the transposon, which is then re-inserted somewhere else. When transposons were first found (in maize), they were referred to as "jumping genes".

Their special property turns out to increase their chance of being reproduced. (They turn out to be "selfish".) That alone probably explains why they are found in so many species. If they happen by accident, they aren't likely to go away. And, they have all the right properties for making the occasional jump from one species to another.


Fitting organisms into an organizing scheme is referred to as taxonomy. Biologists use the Linnean scheme for giving names to species.


An animal with a nerve cord enclosed by a backbone made of vertebrae.

Fish, amphibians, reptiles, birds and mammals are vertebrates.


The scientific study of animals.















Last modified: 7 August 2003

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