The Theory of Evolution

Charles Darwin From England. Med school drop out, Clergy drop out. Parents sent him on a boat to get rid of him.

Came up with the idea of NATURAL SELECTION.

Natural Selection Concept that deals with and explains how EVOLUTION works. Evolution = changes in populations over time.

Fossil Evidence Suggests that species have changed over time. Geologic evidence suggests that simple life forms appeared first followed by more complex.

Darwin’s Voyage Age 21, 1831 Job: ships Naturalist on the HMS beagle. Spent 5 years collecting & making observations.

Galapagos Islands Studied finches (small birds), and other animals. All these animals were unique to the island but similar to other kinds of animals.

Spent the next 22 years collecting, studying, reading and conducting experiments. Then he wrote his book called “ON the Origin of Species by Natural Selection” in 1859.

Meanwhile back at the ranch... Thomas Malthus proposed that populations grow faster than their food supply. He knew that many species produced many offspring but never overran the Earth.

Proposed that there was competition for food, space, mates, shelter, etc. It was a struggle to survive. Which individuals survive?

Darwin had an Answer By breeding pigeons Darwin noticed he could breed birds with favorable traits. Darwin proposes Natural Selection.

Natural Selection Darwin reasoned that organisms survive better if they have certain traits that make them more fit to compete.

Organisms without these traits struggled more and were less likely to survive.

As a result the parents with favorable traits produced offspring with favorable traits, so they were more likely to survive.

Parents without favorable traits produced offspring without favorable traits who were less likely to survive. Until the traits become extinct.

Today’s evidence Volumes of scientific data have been gathered in support of Darwin’s theory. Most scientist accept the theory of evolution as proposed by Darwin.

However... Since the human life span is so short and evolution take millions of years to occur, direct observation is hard to come by.

However... Many studies of organisms with very short life spans have shown conclusive evidence that evolution does occur.

Evidence for Evolution

Structural Adaptations Structural adaptations over time. Teeth, claws, blindness, thorns, quills.

Mimicry - structural adaptation that enables one species to resemble another species. Blow snake rattle its tail like a rattle snake.

Camouflage enables some species to blend into their environment, making it harder for predators to hunt them.

Physiological Adaptations Bacteria in Fleming’s day (1929) were not resistant to antibiotics. Today many are. Weeds, Insects.

Fossils Fossils show a sequence of life from simple to complex. Some fossils look like organisms of today.

Anatomy Homologous structures: The bones of a whale forelimb, crocodile forelimb and a bird wing all have the same bones.

Analogous structures Insect wings and bird winds. Totally different but serve the same purpose. Different ancestors similar way of life, evolved independently of each other

Vestigial structures A body structure that has no function in a present day organism but was probably useful to an ancestor.

Mole rats eyes, they are blind but still have eyes. Humans tail bone, & appendix.

Embryology In the earliest stage of growth many organisms have gill slits, but loose them as they mature. Fish, reptile's, birds, and mammals.

Biochemistry Comparisons of DNA and RNA of different species produce evidence for evolution.

Homework Page 411 #1-6 Worksheet on biochemistry. Do Natural Selection Lab.

Mechanisms of Evolution Gene - codes for a trait Genotype - The actual type of genes you have. (2, 1 from mom, 1 from dad) Phenotype - Outward expression of your genes. Allele - Different manifestation of the same gene.

Populations Genetics and Evolution Darwin developed his theory before genes were discovered. Since then the field of population genetics has been created to help study evolution.

Organisms that have genes (trait) that produce a phenotype (visible trait) that is poorly adapted to the environment, may hamper the organisms ability to survive.

Remember the Natural selection lab? Beads that were easily seen were easily hunted, some to extinction.

Organisms cannot evolve a new phenotype within their lifetime. If your phenotype is favorable you have the advantage over others who do not.

Within a population however, there are many different phenotypes (remember the beads, 100 beads, 10 of each color)

Evolution occurs as a population’s genes and their frequencies change over time.

All the alleles in a population’s genes is know as the gene pool. The larger the gene pool the greater variation you have within the population.

The percentage of any specific allele in the gene pool is called the allelic frequency. Scientists can calculate the frequency of an allele the same way a batting average is calculated.

When the frequency of alleles remains unchanged over several generations it is said that genetic equilibrium has occurred.

Scientist look at different populations and calculate the allelic frequency, to determine if the population is evolving or not.

Causes for changes in genetic equilibrium Mutations: random changes in the DNA caused by radiation, chemicals, or chance.

Most mutations are lethal, some however are useful, thus becoming part of the populations gene pool by natural selection.

Genetic Drift The alteration of allelic frequencies by chance event. Populations becoming isolated. Human populations isolating themselves, religion, etc.

Gene Flow The transportation of genes from one population to another. Genes are lost form one population and added to another.

Natural Selection Still considered the number one cause of evolution.

Natural selection and variations Variations of a single trait sometimes increase or decrease an organisms chances for survival. Stabilizing, directional, disruptive.

Stabilizing Natural selection that favors average individuals in a population.

Average sized spiders survive. Small spiders have a hard time finding food. Large spiders get eaten by predators.

Directional selection Natural selection favors one extreme variation.

Deer with large antlers usually get shot by hunters Deer with small antlers survive better because they are hunted less.

or Forest is infected with insects that bore deep into a trees bark. Woodpeckers with longer beaks could feed on the insect. Woodpeckers with shorter beaks starve and die.

Disruptive selection Individuals with either extreme of a trait’s variation are selected for.

Limpets - sea shell colors range from white, to tan, to dark brown. White Limpets on light colored rocks survive. Dark brown Limpets on dark rocks survive All the tan ones get eaten by birds.

Speciation Species - a group of organisms that look alike and can interbreed to produce fertile offspring. Speciation occurs when members of similar populations no longer interbreed.

Causes of speciation Physical barriers - break a single large population into smaller separate ones. –Volcanoes, canyons, continental drift… This causes geographic isolation.

This decreases the size of the gene pool in the population thus reducing each populations chances to remain like one another.

Reproductive isolation Occurs when formerly interbreeding organisms can no longer mate.

Usually due to a change in the genetic material that causes the populations to become so different that fertilization cannot occur.

Sometimes reproductive isolation is caused by behavior.

One kind of tree frog. Some mate at night, some mate during the day. Eventually they become two separate groups.

Patterns of Evolution Hawaiian honeycreepers found only in Hawaii. 14 different kinds. Very similar body size and structure. Colors and beaks differ sharply

Scientists hypothesize Honeycreepers evolved from a single species. Suggests adaptive radiation

Adaptive radiation When an ancestral species evolves into an array of species to fit the number of diverse habitats.

adaptive radiation is a type of Divergent evolution. Meaning one becomes many.

Occurs when populations adapting to different environmental conditions change to the point they become a new species.

Convergent evolution A pattern of evolution in which distantly related organisms evolve similar traits. Occurs when unrelated species occupy similar habitats in different parts of the world.

Euphorbs in African deserts Cactus in North and South American deserts.

Homework SA 15.2 page 421 #1-5. Vocabulary page 425. CA 15 page 425 # 1-25.