Theories of Evolution
There was a lot of postulation about the theory of evolution way before Darwin’s time. Before Darwin, the earth was thought to be only about 4,000 years old. People believed in the fixity of species and that adaptation is the work of a creator. People also believed that everything that they saw could be explained by Genesis.
Darwin was not the first person to think of evolution. In fact it had been thought of as far back as to
Aristotle and Plato. They believed in “Scala Naturae”, which states that everything can be arranged on a
“ladder” in order of complexity.
Page | 79

During the 1700’s many theories for evolution had come about. Carolus Linnaeus studied “Scala
Naturae” and believed that everything had an ideal form and function and had a place on nature’s ladder.
Erasmus Darwin, Charles grandfather, was a naturalist and doctor. He wrote many books on botany and zoology and within these writings he made footnotes and speculations about the evidence for evolution.
He came up with these thoughts by studying animal development and vestigial structures. Vestigial
structures are structures on organisms that have no apparent function. This suggests that ancestors of that organism once had a use for the structure. For example: some species of constrictors have hip bones.
Count Buffon was a naturalist who wrote a 44 volume natural history of plants and animals. He provided evidence for evolution but just like Erasmus Darwin, he could not explain how it worked. It’s like putting a puzzle together. All of these scientists/naturalists knew the picture on the box, they just didn’t know how to put it together.
Baron Georges Cuvier was a zoologist and the found of the science paleontology, or the study of fossils.
He believed strongly in the fixity of species and special creation until he started to notice that fossils of similar but not the same organisms were found in different strata, or layers of the earth. He proposed that catastrophes, or mass extinctions, had occurred followed by the repopulation by species from surrounding areas. His theory became known as catastrophism.
John-Baptiste de Lamarck offered the first hypothesis for how evolution occurred. He said that complex organisms descended from more complex organisms. He said that is increasing complexity was because of a strive for perfection. He would have been correct had he not said that this increasing complexity was inheritable. He called his theory the inheritance of acquired characteristics. The definition of the inheritance of acquired characteristics states the following: the environment can produce physical changes in an organism during its lifetime that is inheritable. He is most famous for using the example of the long neck of the giraffe.
Page | 80

Lamarck said that the neck of the giraffe is long because the giraffe would stretch its neck to eat the leaves of the higher up branches of the trees. Its neck would stretch in its lifetime and it would pass this trait on to its offspring. We know that this cannot be correct because traits gathered in your lifetime will not necessarily be passed on to your offspring. If you workout everyday and become 300 lbs of pure muscle and you reproduce, your offspring will not come out pure muscle. Evolution takes time and genetic change.
Darwin’s Voyage
Charles Darwin was the naturalist on board the HMS Beagle on its second voyage around the world.
Darwin went to divinity school and while in school he studied geology and biology and other natural sciences. The purpose of the HMS Beagle was to become more acquainted with the natural resources around the world and to gain evidence for creation. The Beagle went all over the world including South
America, Australia, and Africa.
Page | 81

While Darwin was traveling he came up with the thought that the earth must be very old. Once he thought this, he began thinking that if the earth is very old then that would give things time to change, descent with modification. This changed the fixity of species theory during this time.
Darwin also compared animals that were living along with animal remains to animals he knew from where he was from. The study of the distribution of life forms on earth is known as biogeography. While
Darwin was traveling he visited a chain of islands known today as the Galapagos Islands. When he traveled from island to island he began to notice slight differences in the life forms. Two organisms he noticed were the Galapagos tortoises and the famous Galapagos finches.
Page | 82

Darwin noticed differences in the length of the tortoises’ neck lengths. On one island the neck of the tortoises were shorter than some on the other islands. Darwin speculated whether this is because of the low growing vegetation on the islands with short necked tortoises and tall cacti on the island with long neck tortoises. Darwin wondered how the tortoises could look so similar to each other but be separated by large bodies of water.
Once Darwin returned to England he began to put all of his findings together. He came up with the theory of natural selection. Twenty years later he published his book on his findings called On the Origin
of Species by Means of Natural Selection. During these twenty years another man bythe name of Alfred
Wallace also proposed the theory of natural selection and sent his finding to Darwin.
What is Natural Selection?
How did Darwin come up with his theory of natural selection? Natural selection is the mechanism by which species change over time and during this time new species arrive. For natural selection to occur, three conditions must be met.
1.
Individuals within a population must inherit variations that can be passed from generation to generation.
2.
More individuals must be produced than the environment can hold. This produces a struggle to exist or competition between individuals.
3.
Some organisms must have characteristics that enable them to survive better and reproduce better than others. The organisms are termed to be more fit. Fitness is the reproductive success in relation to others.
When these conditions are met, the result a population adapted to its environment. An adaptation is a trait that helps an organism become better suited to its environment and is the product of natural selection.
Page | 83

How do we know that evolution occurs?
Evolution has been a controversial topic since even before Darwin’s time. Today we now consider it a theory and no longer a hypothesis. Today scientists has evidence for evolution including the fossil record, biogeographical evidence, anatomical evidence, biochemical evidence and evidence from developmental biology.
The fossil record is the history of life recorded by the remains of the past. Using fossils we can determine similarities and differences in organisms once living and now alive. The distribution of different plants and animals throughout the world are similar to other life forms from the past in different areas of the world. This is called biogeographical evidence.
Another evidence for evolution is anatomical evidence. Organisms who have structures who have the same structure but different function are called homologous structures. An example of this is the forelimbs of vertebrates. They contain the same bones, but the flipper of a whale and your arm have two clearly distinct functions. Organisms who have structures that are anatomically different but serve the same function are called analogous structures. An example of this is the wing of an eagle and the wing of a butterfly both serve to help the organism fly but are made up of different structures.
During embryological development most vertebrate have a postanal tail and a pair of pharyngeal pouches. This suggests descent from a common ancestor.
Page | 84

All living organisms use the same twenty amino acids and same basic chemical building blocks. This also suggests common descent from a common ancestor. The less amino acid differences, the more closely related two organisms are.
Page | 85