Unit 8: EVOLUTION NOTES

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1 Unit 8: EVOLUTION NOTES Canale LE EVOLUTION is the change in gene frequency in a population over time. Generally, organisms change from simple to more complex, and happens over many generations. **Evolution happens to populations, NOT to individuals!!! Evidence for Evolution The fossil Record: Fossil = the direct or indirect remains of organisms. Direct = skeleton, bones Indirect = footprints Fossils can be found in sedimentary rocks, amber, ice or tar. Fossils show that organisms existed on Earth over 3 billion years ago! Generally, older organisms are found in lower layers of rock strata; younger organisms are found higher in the rock strata. Scientists also found that older organisms are less complex than younger ones. When comparing fossils in undisturbed areas -- fossils in upper strata will resemble those found in the lower strata. ***This suggests a common ancestor!!!

2 COMPARATIVE CYTOLOGY Cytology = study of cells Cells are the basic unit of structure and function for all living things. Many organisms share the same organelles : 1. Cell membrane 2. Ribosomes 3. Mitochondria COMPARATIVE BIOCHEMISTRY Many organisms have similar proteins and enzymes. The closer the relationship between organisms, the greater their biochemical similarities. ***This suggests evolutionary relationships!!*** COMPARATIVE ANATOMY Comparing different organisms reveals similarities in anatomical features. Each figure is adapted for a certain function in their environment. Even though they have some differences, the internal structure of these limbs is similar. Homologous structures are similar and have the same evolutionary origins.

3 Analogous have the same function but have no similarities in evolutionary origin. COMPARATIVE EMBRYOLOGY Comparison of early embryonic development reveals similarities. Human *** What does this suggest? Monkey Common ancestor! Pig Chicken VESTIGIAL STRUCTURES Vestigial structures are remnants of structures that were functional in an ancestral form. Examples: Whales with hind legs Snakes with pelvis and hind legs Suggests a 4-legged ancestor THEORIES OF EVOLUTION Theories of Evolution are attempts to explain the diversity among species. They look at adaptations, which are features which make organisms better suited to survive and reproduce in their environment.

4 Lamarckian Evolution 2 main points: Use and Disuse : New organs arise according to the needs of the organism, and the size of the organ is determined by the degree to which they are used. Example: giraffes with long necks Inheritance of Acquired Characteristics: These useful characteristics acquired by an individual during its lifetime can be passed to its offspring. Why Lamarck was WRONG!! Organisms are NOT able to change physical characteristics just because they want to. Only changes in the DNA of a gamete will be passed on to offspring not changes in body cells. Disproving Lamarck A scientist named August Weismann set out to disprove Lamarck s theory. He cut tails off of adult mice, then allowed them to breed. He did the same experiment for 20 generations of mice ALL the offspring had tails. CHARLES DARWIN Darwin was a British naturalist, who took a voyage on the HMS Beagle, a ship that was supposed to chart the South American coastline. The ship stopped in the Galapagos Islands, and he made observations about the unique animals he found there. ***But they showed similarities to some animals on the S. American mainland Darwin s Theory of Evolution was based on: Variation Natural Selection

5 1. Overproduction: more offspring are produced than can possibly survive. This increases the chance that some will survive to adulthood. 2. Competition: limited amounts of food, water, space, etc. so individuals must compete for resources. 3. Variation: characteristics vary within any species! **What causes the variation??? Combination of genes received from parents!!! 4. Survival of the Fittest: individuals who survive are the ones best adapted to exist and reproduce Fitness = ability to produce offspring that also survive 5. Reproduction: surviving individuals reproduce and pass on their beneficial traits to offspring 6. Speciation: over many generations, favorable adaptations accumulate, gene frequencies change and new species are formed. Which of Darwin s principles do you find in each cartoon? Overproduction Survival of the Fittest Competition MODERN THEORY OF EVOLUTION Modern evolutionary theory supports Darwin s concepts of Variation and Natural Selection -- but adds the genetic basis for variation within populations.

6 Variation is produced by: Mutations Natural Selection *** Mutations are spontaneous and are the raw material for evolution. *** Sexual reproduction involves the sorting and recombination of genes. *** This produces and maintains variation within a population! Natural selection: Involves the struggle of an organism to survive and reproduce in a given environment. ***Keep in mind the mutation or variation happens FIRST!!!!! This gives some organisms a better chance for survival. A selecting agent is something in the environment that changes ( climate, predation, etc) This will allow only those with favorable adaptations to survive and reproduce. Traits which are beneficial to survival tend to be retained and passed on to the next generation. *** This increases the frequency of the gene within the population.

7 Traits with low survival value tend to decrease in frequency from generation to generation. ** If environmental conditions change, traits that had a low survival value may now have greater survival value and may increase in frequency. EVOLUTION IN OUR TIME DDT: pesticide used to kill mosquitoes and black flies. Some had natural mutations that made them resistant to DDT, so they survived to reproduce. They passed on the resistance gene to their offspring, who could survive and reproduce. Eventually, the entire population became resistant to DDT. Bacteria develop antibiotic resistance and pass it to their offspring -- or exchange plasmids between individuals. Darwin s Finches: Found many finches that shared some common characteristics, but had different beaks, sizes, habitats, etc. He realized that there were 14 different species of finch that must have come from one common ancestor! Natural variation within population caused some to be better at eating seeds, some insects. This reduced competition and gave some finches a better chance to survive and reproduce. Adaptive Radiation: different or distinct species will fill different roles in the environment because of variation within the population.

8 Peppered Moth: ( Industrial Melanism) Before the Industrial Revolution in England, more white moths existed. (Lived on white trees, so good camouflage ) Because of variation, some moths were dark, and easily eaten by birds. Industrial Revolution covered the trees in soot, making them dark. Now the light moths were eaten, leaving more dark moths to survive and reproduce. This increased the frequency of the dark gene in the population. *** GEOGRAPHIC ISOLATION: division that separates small groups from the main population by geographic barriers. Can be water, mountains, rivers, highways, climate Each group has variation, but now we have 2 different environments... Some genes may have better survival value in the new environment, and will increase in frequency. In time this will lead to speciation the formation of a new species. WHY?? 1. Different initial gene frequencies 2. Different mutations from the original population 3. Different environmental factors Geographic isolation can lead to reproductive isolation. If the populations have been separated long enough and have become different enough they will not be able to interbreed -- even if the geographic barrier was removed.

9 TIME FRAME FOR EVOLUTION Gradualism Punctuated Equilibrium GRADUALISM: slow, gradual and continuous change. PUNCTUATED EQUILIBRIUM: species have long periods of stability interrupted by brief periods of significant change. HETEROTROPH HYPOTHESIS --- (Origin of Life) Scientists have attempted to explain how early life forms MAY have developed on the primitive Earth. According to the hypothesis: First life forms were not able to synthesize their own organic compounds from inorganic compounds. Atmosphere on primitive Earth contained: Water vapor (H 2O) Hydrogen (H 2) Ammonia (NH 3) Methane (CH 4) Energy from UV radiation, x-rays, lightning and volcanoes changed these compounds into organic molecules.

10 These organic molecules ( amino acids, nucleotides, proteins and sugars ) were carried to the seas by rain and formed a hot, thin soup. These molecules interacted and formed more complex molecules. Experiments performed by scientist Stanley Miller provide support for the theory.