Density

 Evolution

~Descent With Modification

Hillary Clark

The history of all life is explained by evolution. Charles Darwin’s (right) book, “On the Origin of Species”, states that evolution is “the process by which organisms change over time as a result of changes in heritable physical or behavioral traits. Changes that allow an organism to better adapt to its environment will help it survive and have more offspring.” In other words, evolution is descent with modification.

There are two main points that explain descent with modification. First of the two says that all life on Earth is connected and related to each other. Second says that diversity of life comes from modifications in populations driven by natural selection. Natural selection is a huge part of evolution. Survival of the fittest shows one way natural selection helps evolution. Survival of the Charles Darwin

fittest is an organism's ability to survive and reproduce.

Natural selection can change species in two ways, microevolution, and macroevolution. Microevolution is the change of species in small ways (ex. Color, size) over the course of many generations. Macroevolution is when natural selection creates whole new species over time with many changes  (ex. Ancestors of apes turned into humans).

Darwin created the theory of evolution before scientists even knew of DNA. Now, scientists know that physical and behavioral changes happen at a genetic level. These are mutations, which can be caused by random errors in DNA replication or repair. Mutations can advance a species or harm them and cause them to die off.

There is sufficient evidence for evolution, such as rocks and fossils, homologies, and vestigial traits. Rocks can be as old as the planet itself, and sedimentary rock formations can be dated, showing geological time. Fossils hold evidence of extinctions and transitions in evolution. Homologies are similarities between organisms with traits inherited from a common ancestor.  Fossils show the differences between and similarities between modern and extinct species, showing changes over time. Homologous structures explain evolution and possible adaptation purposes from a common ancestor or as a result of the modification. Vestigial traits are structures that lost their function but are similar to ancestral traits. These structures show evidence of modification over time. For example, the tail of a spider monkey is very similar to the human coccyx, which is a vestigial tail.