Chapters 15, 16, and 17 Evolution

The Theory of Evolution Theory – well-tested explanation that unifies a broad range of observations Evolution – change in a kind of organism over time; process by which modern organisms have descended from ancient organisms Can theories change over time? Are theories supported scientifically?

Charles Darwin – 1831 Voyage of the Beagle

Darwin studied: Diversity – he found a wide range of living things well adapted to their environment Fossils – he was curious as to why some were extinct Ground Sloth Fossil

Galapagos Islands Volcanic islands off the west coast of South America Unique species found nowhere else in the world How did this happen?

Galapagos

Darwin Returns Home After Darwin returned home, he studied his notes and specimens He struggled with his observations and how they conflicted with his religion He finally published On the Origin of Species, a book which outlined his theories of natural selection and evolution over time

Darwin’s Influences: James Hutton and Charles Lyell – Geologists whose theories suggested that Earth was extremely old and was always changing slowly over time. Darwin proposed that living things were not fixed in one form, but also changed slowly over time.

Darwin’s Influences: Jean-Baptiste Lamark – proposed the theory of acquired characteristics Use or disuse…some traits were passed down to help survival of offspring False theory

Darwin’s Influences Thomas Malthus – an English economist who studied human population growth He believed that if humans became overpopulated, they would struggle to survive without sufficient resources Darwin applied this to animals and plants and believed it was the driving force for evolution.

Darwin studied variation Darwin did not know about genes, but did observe traits being passed on Artificial selection – when humans choose which traits are to be passed on in animals and plants by selective breeding Examples: Breeds of dogs, pidgeons, cows, corn, Brassica oleraceaeBrassica oleraceae

Darwin proposed Natural Selection The idea that there is a struggle for survival…need to find food, mates, run away, hide, or protect themselves Darwin proposed that some individuals were better adapted for their environment Adaptation - any inherited characteristic that increases an organism’s chance of survival “SURVIVAL of the FITTEST”

Adaptations:

Descent with Modification Darwin proposed Descent with Modification Living things changed over long periods of time due to natural selection He believed that living things evolved from a “common ancestor” “Tree of life” links all living things

Darwin’s early drawing of a tree of life…

Evidence of Evolution: The fossil record

Evidence of Evolution Geographic distribution of living things – different animals on different continents looking similar (marsupial wolf and grey wolf) Animals that are not closely related have similar adaptations

Evidence of Evolution Homologous Structures – structures that have different mature forms but develop from the same embryonic tissues. Vestigial organs remnants of legs in skinks, appendix in humans…

Evidence of Evolution Similarities in Embryology

Chapter 16 – Evolution of Populations Evolution in genetic terms – any change in the relative frequency of alleles in a population. Gene pool – all genes (T, t) present in a population Relative frequency – number of times one allele appears compared to all alleles in the gene pool. (Example: B = 40%, b = 60%) The population is evolving if the frequency changes

Gene Pool allele for brown fur allele for black fur

Sources of Genetic Variation: Mutations – a change in the sequence of DNA. Caused by chemicals, radiation, or just randomly. Can be harmful, helpful, or have no effect. Gene shuffling – genes are recombined during the formation of gametes for sexual reproduction. Does not change gene frequencies on its own. How many genes control one trait?

Single Gene and Polygenic Traits If a trait is controlled by one gene it is called a single-gene trait. Single-gene traits result in only two phenotypes. Example: Tall or Short Polygenic traits result in a range of phenotypes. Example: height of a human being.

Which graph represents a polygenic trait?

Polygenic traits continued… Directional Selection Low mortality, high fitness High mortality, Low fitness

Polygenic traits continued… Stabilizing selection (Example: Birth weight) Low mortality, high fitness High mortality, low fitness

Polygenic traits continued… Disruptive selection Example: Beak Size

Genetic Drift Genetic drift is a random change in gene frequency. Common in small populations Founder effect – a small group migrates away from the original group and has a unique gene pool Examples: Galapagos, Hawaii..

Hardy-Weinberg principle If a population does not evolve, it is in genetic equilibrium. It must: 1. Have random mating 2. Consist of a large population 3. No members move in or out of the group 4. Have no mutations 5. No natural selection occurs Example? Coelacanth?

Hardy-Weinberg Example: videovideo p 2 + 2pq + q 2 = 1 p= frequency of dominant allele q = frequency of recessive allele 2pq = frequency of heterozygotes Sample problem - Brown hair (B) is dominant to blond hair (b). If there are 168 brown haired individuals in a population of 200, then…

Questions: 1) What is the predicted frequency of heterozygotes (Bb)? Answer: 48% 2) What is the predicted frequency of homozygous dominant individuals (BB)? Answer: 36% 3) What is the predicted frequency of homozygous recessive individuals (bb)? Answer: 16% (Easy!)

Speciation Species – a group of organisms that can breed with one another and have fertile offspring Speciation – formation of a new species due to natural selection or chance events

Isolating Mechanisms In order for new species to evolve, groups of organisms must be separated or isolated. If the two groups change enough, and can no longer breed and create fertile offspring, then new species were formed.

Causes of reproductive isolation - Geographical isolation – Groups are physically separated. Ecological isolation- Groups occupy different habitats. Temporal isolation- reproduce at different times of the day. Behavioral isolation- no attraction. Mechanical isolation- structural differences. Reproductive failure- no fertile offspring.

Speciation in Darwin’s Finches:

17-2 Earth’s Early History and 17-4 Patterns of Evolution Earth is about 4.6 billion years old Earth’s early atmosphere probably contained: Hydrogen cyanide Carbon dioxide Carbon monoxide Nitrogen Hydrogen sulfide Water

Where did organic compounds come from? 1950s – Stanley Miller and Harold Urey designed experiments that showed organic compounds could be formed from elements in Earth’s early atmosphere if an electric current was introduced Lightning could provide the electric current Amino acids, cytosine, and uracil could be formed in these experiments.

Miller/Urey’s experiment Mixture of gases simulating atmospheres of early Earth Spark simulating lightning storms Cold water cools chamber, causing droplets to form Liquid containing amino acids and other organic compounds

Organic molecules to cells? Organic molecules can form tiny bubbles called proteinoid microspheres, almost like oil in water RNA may have been the first hereditary material, as it can self-replicate and act as catalysts. These components may have been the first primitive cells…but the exact origin of life is a MYSTERY!

Early Bacteria created Oxygen Cyanobacteria (blue green algae) were probably the first living things to manufacture oxygen Oxygen changed the atmosphere, turned the sky blue, and allowed organisms to respire aerobically (more efficient)

Endosymbiotic Theory Eukaryotic cells may have formed when larger cells engulfed smaller prokaryotes Mitochondria and chloroplasts may have been free-floating bacteria Evidence: They have DNA and ribosomes similar to bacteria and reproduce by binary fission The ability to respire aerobically and the ability to reproduce sexually increased diversity and influenced evolution

Endosymbiotic Theory

Other Topics: Fossils and ancient life Index fossils Radioactive dating Geologic time scale Evolution of multicellular life Mass extinctions

Patterns of Evolution Macroevolution – large scale evolutionary patterns and processes over long periods of time Extinction Adaptive Radiation Convergent Evolution Coevolution Punctuated Equilibrium Changes in developmental genes

Extinction When a species no longer exists on earth Most extinctions were natural until recent times Can be gradual for individuals or can be catastrophic mass extinctions that affect multiple life forms Scientists believe an asteroid impact caused a mass extinction event in the Cretaceous

Adaptive Radiation When a single species or small group of species evolve into many diverse forms over time. Examples: Mammals evolved, finches evolved

Convergent evolution When unrelated organisms that live in similar environments develop similar adaptations to survive

Coevolution The process by which two species evolve in response to changes in each other over time

Punctuated Equilibrium Long, stable periods with little change in species interrupted by brief periods of rapid change Results from small populations, isolated populations, following mass extinctions…

Developmental Genes and Body Plans In some cases, small changes in just a few genes can cause major changes in an organism Hox genes are “master control” genes for animal body plans One change in a gene can lead to wingless, one pair, or two pairs