EVOLUTION AND NATURAL SELECTION Overproduction Genetic Variation Struggle to Survive Successful Reproduction Evolution is defined as the change in species over time. Darwin theorized that evolution occurs through a process known as natural selection. This process is broken down into four parts:

OVERPRODUCTION Overproduction is a process in which each species produces more offspring than will survive to maturity.

GENETIC VARIATION The individuals in a population are slightly different from each other. Each individual has a unique combination of traits, such as color, size, speed, and the ability to find food. Some traits increase the chances of survival and reproduction. These beneficial traits are called adaptations. Variations are genetic and can be inherited.

STRUGGLE TO SURVIVE Because there is only so much food, water, space, and other resources available in the environment, not all individuals will live to adulthood. Those best adapted will have a better chance of survival. Nature, or the environment selects which organisms live and which die. This struggle is often referred to as “Survival of the Fittest”.

SUCCESSFUL REPRODUCTION The individuals that are well adapted to their environment, that is, those that have better traits for living in their environment, are more likely to survive and reproduce. Their traits are thereby passed on to their offspring. The individuals that are not well adapted to their environment are more likely to die early or produce few offspring.

NATURAL SELECTION IN ACTION When an effective insecticide is used on a population of insects, most insects are killed, but few may survive. These survivors have genes that make them resistant to the insecticide.

NATURAL SELECTION IN ACTION The survivors then reproduce, passing the insecticide-resistant genes to their offspring.

NATURAL SELECTION IN ACTION In time, the replacement population of insects is made mostly of individuals that have the insecticide-resistant genes.

NATURAL SELECTION IN ACTION Ultimately, when the same kind of insecticide is used on the insects, only a few are killed because the overall population has become resistant to that insecticide.

EVIDENCE OF EVOLUTION The Fossil Record Homologous Structures Vestigial Structures Embryonic Structures DNA Evidence There are five pieces of evidence scientist use to support the theory of evolution. They are:

THE FOSSIL RECORD Fossils are the preserved remains or traces of an organism that lived in the past. The millions of fossils that scientists have collected, is called the fossil record.

THE FOSSIL RECORD According to the fossil record, over 90% of the organisms that once lived on the Earth are now extinct. In addition, there is no fossil evidence that organisms alive today were here long ago. However, the organisms alive today have features that resemble life of the past. What happened to the species that lived long ago, and where did the life of today come from? The evolutionist explanation is that species from long ago have changed into the species alive today.

HOMOLOGOUS STRUCTURES Scientists have observed that many different organisms have structures that are quite similar. For instance, when comparing a human hand, cat leg, dolphin flipper, and a bat wing, we find nearly identical bone patterns. Why would structures specialized for such different functions such as grasping, walking, swimming and flying be so similar? The evolutionist conclusion is that these different animals must have evolved from a common ancestor.

VESTIGIAL STRUCTURES Vestigial structures are structures that no longer serve a function in the living organism. For instance, humans have a tail bone that serves no apparent function. In addition, the modern whale has a series of bones near the base of the skeleton that resemble hip bones. Hip bones serve the function of allowing land animals to walk. Why would a whale have hip bones? The evolutionist conclusion is that the whale must have evolved from a land walking creature.

VESTIGIAL STRUCTURES Fossil evidence also supports the theory that the modern day whale evolved from a land walking animal. 55 Million Years Ago 50 Million Years Ago 40 Million Years Ago 46 Million Years Ago

EMBRYONIC STUCTURES A developing baby is called an embryo. Embryos of very different organisms such as a chicken, rabbit, and human have embryos that look nearly identical. During the early stages of development, all have a tiny tail and gill slits in their throats. The conclusion is that all of these organisms have a common ancestor. It is thought that the embryo is like a window through evolutionary time. The ancestors of these species once had tails and gills.

DNA EVIDENCE The DNA that codes for all life on this planet is composed of the same four nitrogen bases, adenine, guanine, cytosine, and thymine. In addition, this coded message creates the same twenty amino acids that builds all life forms on the planet. This similarity, according to the theory of evolution, suggests that all life on the planet has evolved from a common ancestor.