1. The Theories of Evolution
Species change over time!!!

2. Species evolve (change) over time.
Evolution is the consequence of the interactions of
(1) the potential for a species to increase its numbers
(2) the genetic variability of offspring due to mutation and recombination of genes
(3) a finite supply of the resources required for life
(4) the ensuing selection by the environment of those offspring better able to survive and leave offspring

3. Evolutionary Foundation
Hutton and Lyell helped scientists recognize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present.
Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species = Adaptation
Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.

4. Introducing Evolutionary Theory
We share Earth with millions of other organisms (variety of living things) = Biological Diversity
How is everything so different?
Evolution = change over time leading to modern organisms that have descended from ancient organisms
Theory = well-supported testable explanation of phenomena that have occurred in the natural world

5. Introducing… Charles Darwin!
In 1831, Darwin set sail on the Beagle for a voyage around the world
During his travel, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time = The Theory of Evolution
Darwin used these observations to scientifically explain the diversity of life on this planet.

6. The Galapagos Islands
Darwin observed that the characteristics of many animals and plants varied noticeably among the different islands.
Pinta Island Intermediate shell
Isabela Island
Dome-shaped shell
Hood Island
Saddle-backed shell

7. Natural Variation & Artificial Selection
Natural Variation = differences among individuals of a species
Variations can be inherited from one generation to the next
Selective breeding = humans select desirable traits and breed based on natural variation (to improve crops/farms)
Darwin called this artificial selection = nature provides variation among different organisms, and humans select variations they found useful.

8. Evolution by Natural Selection
Living things evolve as the result of:
The struggle for existence
The survival of the fittest
The descent with modification
Peacock tail evolution:

9. Struggle for Existence
Darwin was convinced artificial selection worked in nature as the result of overproduction and competition for resources = struggle for existence (members of each species compete regularly to obtain food, living space, and other necessities of life)
Depends on an individual’s ability to survive and reproduce = fitness
Fitness results from adaptations = inherited characteristics that increase an organism’s chance of survival
= “Survival of the Fittest!”

10. Natural Selection Survival of the fittest = Natural Selection!
Traits are being selected and increasing over time (over many generations without human influences)
Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment.

11. Descent with Modification
Over time, natural selection produces organisms with different structures or functions resulting in species that look different from their ancestors
Each living species has descended with changes from other species over time = Descent with Modification
Then, all living things must be related!
There’s a common ancestor of all living things = Common Descent

12. Evidence of Evolution
Living things have been evolving on Earth for millions of years. Evidence of this process could be found in:
The fossil record
The geographical distribution of living species
Homologous structures of living organisms
Similarities in development

13. Fossil Record
Remember: Fossils are the remains of ancient life and different layers of rock were formed at different times.
Fossils in different layers of rock are evidence of the gradual change over time (different species appeared, lived for a time, and then vanished)

14. Geographic Distribution
Populations in different places adapted to different environments… different species descended with modification from a common ancestor.
Different species living in similar environments in different parts of the world sometimes have similar structures and functions because they experienced similar pressures of natural selection

15. Homologous Structures
Some vertebrates have similar bone structures that develop from a specific group of cells in an embryo, but the structures adapted different functions so the organism can survive in different environments providing evidence of descent with modification from common ancestors
Homologous Structures = they appear and function differently, but develop from the same embryonic tissues
Some homologous structures provide little or no function in some organisms = vestigial organs

16. Similarities in Development
Embryos of many vertebrates look very similar in the early stages of development.
The same groups of embryonic cells develop in the same order and in similar patterns producing homologous structures

17. Summary of Darwin’s Theory
Individual organisms in nature differ, and some variation is inherited
Organisms in nature produce more offspring than can survive and reproduce
Members of each species compete for limited resources
Unique organisms have different advantages and disadvantages in the struggle for existence
Individuals best suited to their environment survive and reproduce, passing the characteristic to their offspring. Individuals without the characteristic die
Species change over time due to natural selection… new species arise and others disappear
Species alive today have descended with modification from species of the past
All organisms on Earth are united by a common descent