1. Evolution and Natural Selection

2. Evolution vs. Natural Selection
Evolution- Process by which modern organisms have descended from ancient organisms
Natural Selection- Process where organisms better adapted to their environment tend to survive and produce more offspring

3. Evolution - Early Ideas of Jean-Baptiste Lamarck
Jean-Baptiste Lamarck developed the first attempt at a theory of evolution in the late 1700s (Theory of Transformation)
Believed that organisms could change during their lifetimes by selectively using or not using various parts of their bodies
Example: believed that if a giraffe stretches its neck reaching for leaves, its neck will grow longer and pass that feature down to future generations
Flaws in theory
Did not hold up when tested with experiments
Couldn’t explain how certain features developed
Important ideas which resulted from his theory
Evolution takes place by small gradual steps
Proposed that simple organisms could develop into more complex organisms over many generations

4. Natural Selection- Observations and Ideas of Charles Darwin
Charles Darwin proposed that all species of life have descended over time from common ancestors
Many of his ideas came from observations made during a 5 year trip around the world on the HMS Beagle
Compared organisms found on different Galapagos Islands to organisms that lived elsewhere
Noticed similarities and differences of among the species he studied
Realized that island species had become different from their mainland relatives over time

5. Darwin’s Research
Darwin collected birds (finches) from several of the Galapagos Islands
Noticed that the birds were different from one island to the next
Concluded that the finch species were all related to a common ancestor species that came from the mainland
Overtime, different finches developed different beak shapes and sizes suited to the food they ate
The beak shape is an example of adaption (an inherited behavior or physical characteristic that helps an organism survive and reproduce in its environment)
Based on his observations, Darwin hypothesized that species change over many generations and become better adapted to new conditions

6. Darwin’s Search to Determine Evolution’s Mechanism for Change
Mechanism- The natural process by which something takes place
Artificial Selection- Process by which humans use animal and plant breeding to selectively develop particular traits by choosing which animas or plants reproduce and have offspring
Natural Selection- Process that results in the adaption of an organism to its environment by means of selectively reproducing changes in it genotype
Organisms better adapted to their environment tend to survive and produce more offspring
Organisms that are not well adapted to their environment may die without reproducing
Darwin published his theory on natural selection in his book “The Origin of Species”

7. How Natural Selection Works
Darwin identified three factors that affect the process of natural selection: Overproduction, variation, and competition
Overproduction- When species reproduce more offspring than can survive due to the available resources
Variation- Members of a population differ from one another in many of their traits
Such variations are hereditary, passed from parents to offspring through genetic material
Competition- The struggle among living things to get the necessary amount of food, water, and shelter
In many species, so many offspring are produced that there are not enough resources for all of them- this is why natural selection is often referred to as “the survival of the fittest”

8. Environmental Changes and Natural Selection
A change in the environment can affect an organism’s ability to survive and may lead to natural selection
Darwin proposed that, over a long time, natural selection could lead to change, where helpful variations accumulate in a population and unfavorable ones disappear
Examples:
Plants that are drought resistant have replaced those that are not in areas that have little precipitation
Trees that are better able to withstand strong winds (shorter and have thick trunks) out number others in areas with frequent wind storms
Dark colored moths, rather than lighter ones, survived in an area in the UK where soot darkened the trees

9. Genes and Natural Selection
Only traits controlled by genes can be acted upon by natural selection
Sexual reproduction causes existing gene variations to be recombined in each member of a population
Genetic variations contribute to the diversity of organisms
To get a new variation, there must be a gene mutation
Only mutations to reproductive cells can be passed on to an offspring
If offspring are born with a mutation, natural selection will determine whether that mutation gets passed onto the next generation
Epigenetic changes- small changes to DNA that turn genes on or off but do not change the genetic code itself
Small chemical changes to DNA affect how genes get expressed
Offspring can inherit these changes from their parents or grandparents

10. Mutations and Evolution
Over time, as individual organisms successfully respond to changing conditions in the environment, the population evolves and its fitness (how well it can survive and reproduce in its environment) increases
Mutations are necessary for evolution to occur
Not all mutations are harmful
Mutations that increase fitness tend to grow more common in a population
Mutations that decrease fitness tend to disappear as those individuals die or reproduce less successfully
Mutations create variations among members of a species and account for the diversity of organisms on Earth

11. How Gene Flow and Genetic Drift Affect Evolution
Gene Flow- Occurs when individuals with new alleles physically move from one population to another
Introduces new alleles into a population
Can increase the genetic variation of a population
Genetic Drift- A random, directionless mechanism of evolution where some alleles are lost to a population
As an example, if the only organism carrying a specific allele dies, that genetic information would be lost to future generations of the population
Through random chance, the genetic variation of the population shrinks

12. Sexual Selection and Evolution
Sexual Selection- A type of natural selection that acts on an organism’s ability to get the best possible mate
Sexually reproducing organisms try to choose mates with specific traits that have higher fitness (will result in offspring with greater fitness)
Female choice- In species where females choose their mates, natural selection favors traits that help females choose mates with higher fitness
Example: If male ducks with brighter feathers have higher fitness, females will evolve a trait that causes them to choose males with bright feathers and males will evolve to have even brighter and fancier feathers
Male competition- In species where males compete to control a territory with access to females, natural selection will favor traits that give males an advantage in competition
This may cause males to evolve exaggerated characteristics like extra-large horns, pinchers, or bodies
Sometimes the evolutionary adaptions end up having a negative impact on the population
Even after the bright feathers start to hurt the males survival, by make them more of a target for predators, the females may continue to select the males with bright feathers
The need to reproduce may cause males to evolve exaggerated characteristics that make them less likely to survive

13. Coevolution
Coevolution- the process by which two species evolve in response to changes in each other over time
Occurs when species with close interactions affect each others evolution
Can happen when two species cooperate with each other (ex: flowering plants and pollinators like birds or bees)
Can occur when species compete for resources and in species involved in prey-predator or host-parasite relationships

14. Evidence for Evolution
Fossil record- (all the fossils that have been discovered) provides evidence about how organisms of the past have evolved into the forms seen today
Comparisons of anatomy- Similarities in the structure of the bodies of different organisms provide clues that organisms evolved from a common ancestor
Example: Similarities inn the wing of a pterosaur, the wing of a bat, the flipper of a dolphin, and a human hand are evidence of common ancestry
Genetic evidence- Every living thing uses DNA for its genetic material
This shared use of DNA is evidence that every organism on Earth has a common ancestor
This common ancestor , called LUCA (last common ancestor), was most likely a single celled organism similar to modern bacteria
Branching tree- A diagram that shows how groups of organisms may be related
A species is more closely related to a species on the same branch than to one on another branch