Evolution

Theories on the Origin of Life Spontaneous generation is the theory that life can come from non-living matter. (Frogs come from mud, flies come from garbage, etc.) Disproved by Redi (1600) – covered materials don’t produce flies. Spontaneous generation of microbes was disproved by Louis Pasteur (1860) Heterotroph Hypothesis–life arose from a combination of inorganic chemicals methane (CH4) ammonia (NH3) + water (H2O) that existed in the ancient oceans of earth. Miller and Urey experiment (1953) formed amino acids Fox – amino acids will form proteins at high temperatures Problem – no CELLS have ever been produced in a lab!

Jean Baptiste LaMarck 1809 Early Theory of Evolution (gradual changes in species over time) Use and Disuse – He hypothesized that organisms were able to develop new structures as they needed them and they were able to pass them on to their offspring. This was called the.. Theory of Inheritance of Acquired Traits Got evolution right, but got mechanism wrong !! Inherited Traits – characteristics genetically passed on the offspring. Acquired Characteristics – a trait that develops during an individual’s lifetime.

Mechanisms of Evolution Natural Selection Sexual Selection / Non-random mating Mutation Gene Flow: movement of alleles between populations Ex: When organisms migrate into/out of a population Hardy-Weinberg principle - genetic equilibrium = no gene flow. Genetic Drift- reduces population size by chance! Bottleneck effect Founder effect

Charles Darwin “Father of Evolution” 1809-1882 Ships naturalist aboard the HMS Beagle collected hundreds of specimens and made extremely detailed observations of the natural world on the 5 year scientific expedition. Upon his return and further study of geology and natural population increase, he developed his Theory of Natural Selection Wrote (1845) his famous book “The Origin of Species”

Darwin’s Theory of Natural Selection #1 Overproduction Organisms tend to have many more than two offspring so at least some will survive (yet populations usually do not grow rapidly in the wild) #2 Competition Therefore they must compete for resources (food, space, mates)

Natural Selection #3 Variation - variation within the population. #4 Adaptation - some of them must be better adapted to their environment

Fitness Which is more fit??? Fitness is a measure of the relative contribution an individual trait makes to the next generation. Helpful traits…camouflage and mimicry

#5. Natural Selection- the ability of organisms that are best adapted to survive and reproduce . Those that are less well adapted will not survive.

Evidence for Evolution All of the fields of Life Science show evidence of evolution. A. The Fossil Record Fossil: the remains or evidence of past life recorded in rock. (molds, impressions, bones, shells, teeth, preserved in ice, etc.) 1. Fossils are found most often sedimentary rock. 2. Relative age can be determined by the fossils position in the layers. The oldest fossils are found below the younger ones. 3. Absolute dating uses the principal of radioactive dating The half-life of known radioactive compounds never changes. (ex. Carbon 14 found in bones and shells can determine their actual age in years). Ex. Fossil remains clearly show the gradual evolution of the modern horse.

Speciation Eventually, over generations and time, new species will evolve from older forms by natural selection of better adapted forms.

Fossil Record

B. Comparison of Similar Anatomy or Structures 1. Homologous structures - those that appear to have come from a common ancestor. These indicate that species are related. Ex. Bats wing, human arm and whale flipper bones. 2. Analogous structures - those that are used for the same function but are not similar. These indicate species are not related. 3. Vestigial structures – those that no longer serve a useful function Ex. Human appendix, tailbone (coccyx)

Bones of the Mammalian Forelimb

Comparative Anatomy

Cell Structures Cytological – comparison of cell structures ex. Eukaryotic vs. prokaryotic cells (nucleus) (no nucleus)

Comparative Embryology Comparative Embryology – examination of differences and similarities in embryo development (before birth). ex. Comparison of bird, fish and early human embryos

E. Behavior Comparisons

Biochemical Comparisons F. Biochemical Comparisons Recent developments (Human Genome Project) have allowed for the comparison of DNA from different species and groups within species. This new evidence is the strongest yet that consistently supports accepted evolutionary theory. DNA - our DNA and that of a Chimpanzee is more than 99% identical. Gorillas and Baboons have somewhat less (95-97%) and mice have 80% identical DNA. Protein and Enzymes Ex. Cytochrome C, a respiratory enzyme common to all animals is slightly different in different species. Humans differ from monkeys by one amino acid in their cyt C. We differ from pigs by 10 amino acids. Chicken cyt C has 13 different amino acids and fish differ by 21. This clearly shows the accepted evolutionary relationship between vertebrates.

Molecular Comparisons

Sources of Variation A mutation is a change in the DNA of an organism due to external or internal factors. (toxins, radiation, random,etc.) Most mutations are NOT beneficial to the organism. Some may become beneficial if the environment changes, provided they do not harm the individual. (ex. Giraffe’s neck)

Genetic Recombination Sexual reproduction leads to new combinations of genes. Ex. You are not exactly like either one of your parents.

C. Speciation New species will arise more quickly if they are geographically isolated. Natural barriers such as mountains, deserts, rivers or landslides can separate members of a population. If they can no longer interbreed they may change enough by natural selection to become a separate species. (ex. Darwin’s finches) The loss of the ability to interbreed is called reproductive isolation. Sometimes this is caused by changes in reproductive organs such that the offspring will not survive. Sometimes this type of isolation is caused by changes in courtship behavior or the timing of mating cycles.

Speciation Geographic isolation of populations Can lead to Reproductive isolation of population New Species (unable to breed when together)

Geographic Isolation Members of a population may become isolated from one another by geographic boundaries like mountains, rivers or even oceans

Reproductive Isolation Genes are not compatible to mate so they can not interbreed

Adaptive Radiation the diversification of a group of organisms into forms filling different ecological niches

New Species Evolve

V. Evolutionary Time Frames Gradualism: species descend from a common ancestor gradually as the change in minor ways over a long period of time. Seen often in the fossil record of marine invertebrates like snails.

Punctuated Equilibrium B. Punctuated Equilibrium a newer theory developed by Stephen Jay Gould states that species remain fairly constant over long periods of time until a great change in their environment cause relatively rapid speciation. Seen in the evolution of birds from dinosaurs

Convergent Evolution – when different species adapt similarily due to living in similar environments

Divergent Evolution – tracking organisms back to a common ancestor (Adaptive Radiation)

II. Genetic Drift Refers to changes in the allele frequencies of a gene pool due to chance (random) Not due to natural selection

Genetic Drift Example A population of 10 frogs includes 3 red frogs, 5 light green frogs, and 2 dark green frogs. By chance, the three red frogs die and only the green frogs reproduce and pass on their genes. The allele frequencies of the next generation’s gene pool may be completely different from previous generation.

Natural Selection vs. Genetic Drift

C. Types of Genetic Drift Bottleneck Effect Occurs when an event causes a significant percentage of the population or species to be killed or otherwise prevented from reproducing Often caused by natural disasters or human interference Population is reduced by 50% or more Reduces population’s ability to adapt to changes in environment Bottleneck Effect Model

Types of Genetic Drift (cont.) Founder Effect Occurs when a few individuals found a colony and only a fraction of the total genetic diversity of the original gene pool is represented Alleles that are carried by the founders is due to chance (from their parents) Example: Amish population recessive allele for unusual form of dwarfism (affects only lower arms & legs) and/or allele for polydactylism (extra fingers) In non-Amish population, only 1 in 1,000 has this allele Isolated religious sect that descended from a few German ancestors As many as 1 out of every 14 people carry a recessive allele