A change in a species is also known as evolution. Evolution is defined as a change in the gene pool (DNA sequencing) of a population in response to various stimuli 9environmental factors) by a species over time. This change is evident to scientists in a variety of ways: fossils, DNA sequqnces, anatomical similarities, physiological similarities, and embryology.

Theory of Evolution
  • Variation exists within the genes of every population or species (as a result of random mutation).
  • In a particular environment, some individuals of a population are better suited to survive and to have more offspring.
  • Over generations, the traits that make certain individuals of a population able to survive and reproduce tend to increase in that population.
  • Evidence from fossils and many other sources indicates that living species evolved from species that no longer exist.

Evidence of Evolution
Type of Evidence
What Evidence Reveals
The fossil record
intermediate forms
gradual modification of species over time
Geographic distribution of living species
similar animals in different locations
different lines of evolutionary descent
Homologous body structures
different mature forms develop from same embryonic tissues
species are descended from common ancestors
Similarities in early development
the order and pattern of development in vertebrate embryos
vertebrates share a common ancestry