What is Evolution?

First and foremost, evolution is a theory. The term "theory" represents an idea that is suggested or presented as possibly true but that is not known or proven to be true. Evolution is a concept that not everyone agrees with, but still, there is evidence to support it. Evolution is the idea that the differences between modern plants and animals are because of changes that happened by a natural process over a very long time. Even though there is much opposition to the theory of evolution, there is a reason it is not discarded. Though there is no way to be certain evolution is true, there is mountains of evidence to support that it is a fact, this is why theories are able to be accepted.

The History of Earth

Years ago /Event

  • 4.6 billion /The Earth forms and is bombarded by meteorites and comets
  • 3.8 billion /Replicating molecules (the precursors of DNA) form.
  • 3.5 billion /Unicellular life evolves. Photosynthetic bacteria begin to

release oxygen into the atmosphere.

  • 555 million /Multi-cellular marine organisms are common.
  • 500 million /Fish-like vertebrates evolve.
  • 450 million /Arthropods move onto the land.
  • 420 million /Land plants evolve, creating new habitats.
  • 360 million /Four-limbed vertebrates move onto the land as seed plants.
  • 250 million /The supercontinent called Pangea forms.
  • 248 million /Over 90% of marine life and 70% of terrestrial life go extinct during the Earth's largest mass extinction.
  • 225 million /Dinosaurs and mammals evolve. Pangea begins to break apart.
  • 130 million /The earliest flowers evolve, and dinosaurs dominate the landscape.
  • 65 million /A massive asteroid hits the Yucatan Peninsula, and ammonites and non-avian dinosaurs go extinct. Birds and mammals are among the survivors.
  • 4 million /In Africa, an early hominid lives. The ice age begins.
  • 130,000 /Anatomically modern humans evolve.

Dating Fossils and Rock

Relative Dating - Rocks and sediments are deposited on the earth in layers. Unless the earth has been badly disturbed, for example by an earthquake, then the oldest layers of rock will be at the bottom and the newest will be at the top. By looking at the layers, scientists can determine what order they were deposited in, although they still do not know the exact dates of the rock, it gives them a relative idea.

Absolute Dating - For rocks that are relatively young, the best way of finding this out is to use carbon dating. Carbon is found in rocks, plants, animals and other living things. After an organism dies, the proportion of Carbon-14 atoms begins to decrease. By studying the proportion of Carbon-14 atoms, compared to the other carbon atoms, scientists can find out how old rocks and fossils are.

Radiometric Dating - The universe is full of naturally occurring radioactive elements. Radioactive atoms are inherently unstable; over time, radioactive “parent atoms” decay into stable “daughter atoms.” When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside. Afterwards, they decay at a predictable rate. By measuring the quantity of unstable atoms left in a rock and comparing it to the quantity of stable daughter atoms in the rock, scientists can estimate the amount of time that has passed since that rock formed.


The fossil record provides snapshots of the past that, when assembled, illustrate a panorama of evolutionary change over the past four billion years. Each new fossil contains additional clues that increase our understanding of life's history and help us to answer questions about their evolutionary story.

Transitional Fossils

A transitional fossil is any fossilized remains of a life form that exhibits traits common to both an ancestral group and its derived descendant group. Transitional fossils are strongly suggestive of evolution because they indicate the progression of organisms, just as evolutionary theory predicts.


Different structures on organisms have the capability of providing evidence for the theory of evolution. Examination of two types of structures, vestigial and homologous structures, provide proof that throughout billions of years, different organisms have evolved different uses for the same structures, or developed adaptations that allow structures to become unnecessary.

Vestigial Structures

A strong and direct evidence for common descent comes from vestigial structures. The existence of vestigial organs/structures can be explained in terms of changes in the environment or modes of life of the species. Those organs/structures are typically functional in the ancestral species but are now either nonfunctional or re-purposed. Examples are the pelvic girdles of whales, the hind wings of flies and mosquitos, wings of flightless birds such as ostriches.

Homologous Structures

Homologous Structures have similar bones, muscles, and nerves as other organisms from different species. These structures are alike due to their similar embryonic origin. Although they have similar body structures, the functions of these bones, muscles, and nerves are different depending on the organism. For example, porpoises and birds both have similar forearm structures but the bird uses these bones, muscles, and nerves to fly while the porpoise uses them to swim.


Embryology also supports the theory of evolution for many reasons. The first, obviously is the concept of growth of an embryo. Anyone who has seen an ultrasound picture knows that there is a huge difference between how a person looks as an embryo and how they look as a baby. This is evolving, the embryo evolves the traits, the looks that they need to thrive in life. Additionally, have you ever noticed that the embryo of a squirrel may appear similar in looks to the embryo of a human baby? This also provides evidence for evolution, as anyone who didn't know better would think they are the same organism, this could mean that at some point, one evolved from the other.


As everyone knows, DNA is a molecule which is in almost every cell in our body. It carries the instructions needed to build an organism, a bit like building blue prints or an instruction manual, and is passed on from generation to generation during reproduction. All living things on our planet use DNA as their instruction manual which is a clue in itself. That fact suggests all life is related, following the concept of evolution. When DNA is analyzed, you can find some of the same chunks of DNA in bacteria as in humans. When you look at more closely related organisms you can see their DNA is increasingly similar. For example, the DNA sequences of humans and chimpanzees are about 97% identical.


Biogeography is the study of how species are scattered across the planet, and how they got that way. In the 1840's, a scientist named Russel Wallace noticed a pattern of species in certain ranges around the world. On his trips through the Amazon and Southeast Asia, he sought to demonstrate that evolution did indeed take place, by showing how geography affected the ranges of species. He studied hundreds of thousands of organisms, carefully noting exactly where they were found. The patterns he noticed were compelling evidence for evolution. For example, he was amazed by how rivers and mountain ranges marked the boundaries of many species' ranges. The conventional explanation that species had been created with adaptations to their particular climate made no sense since he could find similar climatic regions with very different animals in them. Wallace came to the conclusion that biogeography was simply a record of inheritance.