Evolution & Natural Selection

Vocab Evolution - change in a kind of organism over time; process by which modern organisms have descended from ancient organisms Theory - well-tested explanation that unifies a broad range of observations

Voyage of the Beagle (1839 - 1844) Darwin’s Voyage - During his travels, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time. What was it?

Galapagos Islands During his travels, Darwin was amazed how different organisms were so well adapted to many different environments. (“Perfect fit”) He saw patterns of diversity Not just in living organisms, but also in fossil records. The Galapagos Islands were a microcosm of Evolution

Darwin’s Finches

Development of Evolutionary Theory What could cause such great diversity? Why have so many species died out? Why have some species not changed at all? Charles Darwin offered an explanation based on careful observations.

Idea’s that shaped Darwin’s Thinking James Hutton and Charles 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. Thomas Malthus (English Economist) - reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone. Jean-Baptiste Lamarck 1809 - 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

Lamarck (His theory is wrong) Tendency Toward Perfection Innate tendency toward complexity and perfection Birds acquired the urge to fly Kept trying to fly Use and Disuse Using a trait (wings) causes them to become stronger and larger Disuse causes it to disappear Inheritance of Acquired Traits Passing acquired traits from one generation to the next

Lamarck

“The Survival of the Fittest” Evolution Development of Evolutionary Theory “The Survival of the Fittest” But … What determines Fitness???

Development of Evolutionary Theory Darwin Concluded: Physical traits and behaviors enable organisms to survive and reproduce (Fitness) Fitness results from adaptations Darwin reasoned that adaptations result from natural selection and result in evolution Evolution is the process by which living things change and diversify over time

Natural Selection

Premises of Natural Selection Evolution Through Natural Selection Premises of Natural Selection Populations overproduce. Resources are limited, so competition ensues. Genetic variations directly impact the ability of organisms to survive. Organisms with beneficial differences will have a better chance of survival. Surviving individuals pass their traits onto future generations. This results in a slow change in populations over time.

Evolution Through Natural Selection These end results can be attributed to 3 distinct selection type models. All of which are as a result of environmental pressures. Directional Selection Stabilizing Selection Disruptive Selection

Directional Selection Evolution Through Natural Selection Directional Selection form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

Directional Selection Evolution Through Natural Selection Directional Selection

Directional Selection – e.g. Evolution Through Natural Selection Directional Selection – e.g.

Stabilizing Selection Evolution Through Natural Selection Stabilizing Selection form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

Stabilizing Selection Evolution Through Natural Selection Stabilizing Selection

Stabilizing Selection – e.g. Evolution Through Natural Selection Stabilizing Selection – e.g.

Evolution Through Natural Selection Disruptive Selection form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

Evolution Through Natural Selection Disruptive Selection

Disruptive Selection e.g. Evolution Through Natural Selection Disruptive Selection e.g. What will disruptive selection eventually result in?

WHY? Are we as Human Beings exempt from Natural Selection? QUESTION??????? Are we as Human Beings exempt from Natural Selection? WHY?

QUESTION??????? Biologists believe that Achaebacteria living today are similar to ancient achaebacteria. Many of these are found in extreme locations. Some scientists believe that this provides a good example of the origins of life. Why do you think that these organisms have not changed over the years? Why would understanding the origins of life on earth help with discovering life on other planets?

Genetic Drift Genetic Drift - random change in allele frequencies that occurs in small populations In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population. founder effect - change in allele frequencies as a result of the migration of a small subgroup of a population

Genetic Drift and Founder Effect

Does Evolution occur all of the time?

Hardy-Weinberg principle The principle that allele frequencies in a population will remain constant unless one or more factors cause the frequencies to change If there are no factors causing allele frequencies to change then the population is in…….. genetic equilibrium - situation in which allele frequencies remain constant

Genetic Equilibrium Five conditions are required to maintain genetic equilibrium from generation to generation: random mating the population must be very large there can be no movement into or out of the population no mutations (that filter into the gene pool) no natural selection

Do Now….. Describe how natural selection can affect traits controlled by single genes. Describe three patterns of natural selection on polygenic traits. Which one leads to two distinct phenotypes? How does genetic drift lead to a change in a population’s gene pool? What is the Hardy-Weinberg principle?

When evolution DOES OCCUR The process of SPECIATION - formation of new species Speciation has occurred when – population have become reproductively isolated from one another reproductive isolation - separation of species or populations so that they cannot interbreed and produce fertile offspring Reproductive isolation can develop in a variety of ways, including behavioral isolation, geographic isolation, and temporal isolation.

Behavioral Isolation Examples form of reproductive isolation in which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding Examples Mating calls Mating dances

Geographic Isolation form of reproductive isolation in which two populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water

Temporal Isolation form of reproductive isolation in which two populations reproduce at different times

Speciation of Darwin’s Finches Speciation in the Galápagos finches occurred by the: founding of a new population geographic isolation changes in the new population’s gene pool reproductive isolation ecological competition