The Formation of Earth Earth’s Age Scientists think that Earth formed more than 4 billion years ago by the accumulation of dust and debris moving through space. Radiometric Dating The ages of rocks and other materials can be determined by measuring the amount of radioactive decay that has occurred in radioactive isotopes found in samples of those materials. An isotope’s half-life is the time that one-half of a sample of the isotope takes to decay.

Radioactive Decay Example: Potassium-40’s half-life is 1.3 billion years After 1.3 billion years, it has been reduced by half After another 1.3 billion years (now a total of 2.6 billion), it is reduced again by half, so 1/4 of the original amount remains After another 1.3 billion years (now a total of 3.9 billion), it is reduced again by half, so 1/8 of the original amount remains

The First Cells The first cells that formed on Earth were probably anaerobic, heterotrophic prokaryotes. Chemosynthesis The first autotrophic cells probably used chemosynthesis to make food. Chemosynthesis produces energy through the use of inorganic substances, such as sulfur (instead of sunlight)

The First Eukaryotes Eukaryotic cells may have evolved from large prokaryotic cells that engulfed smaller prokaryotic cells. This is known as the theory of endosymbiosis. The engulfed prokaryotic cells may have become the ancestors of organelles such as mitochondria and chloroplasts.

Change in a species over time “Nothing in biology makes sense except in the light of evolution” ~Theodosius Dobzhansky (1900-1975)

In science, theories are statements or models that have been tested and confirmed many times Can be used to make predictions Can be changed as new evidence is found

Why do so many different animals have the same structures, the arm bones in a human are the same bones as a flipper in a whale? Why is the sequence of DNA very similar in some groups of organisms but not in others? Why do the embryos of animals look very similar at an early stage?

Charles Darwin developed the THEORY OF EVOLUTION BY NATURAL SELECTION, which explained how organisms changed over time  (ADAPTED)

Lamarck's Theory of Acquired Characteristics Thought that you would gain or lose features if you overused or didn't use them, and that these changes would be passed to offspring  PROVEN TO BE WRONG!

Darwin was a naturalist (what we today call biologists) He traveled the world and made observations and sketches of many species His most famous travels were aboard the H.M.S. Beagle where he traveled to the Galapagos Islands

Darwin published this work to explain the variety of species that exist on the planet He proposed the “Theory of Evolution by Natural Selection”

Darwin noted that there existed many finches on the islands, but while they had similarities, each was adapted to eating a particular type of island food He concluded that the finches all came from one ancestral species and evolved into many new species Cactus finch, photo courtesy of zrim, flickr creative commons

Darwin’s Ideas Descent with Modification Natural Selection Darwin wrote On the Origin of Species, in which he argued that: Descent with modification occurs, in that species descended from common ancestors, and that natural selection is the mechanism for evolution. Natural Selection Organisms in a population adapt to their environment as the proportion of individuals with genes for favorable traits increases. Those individuals that pass on more genes are considered to have greater fitness.

Natural Selection

1. Variation exists among individuals in a species. 2 1. Variation exists among individuals in a species. 2. Individuals will compete for resources (food, mates, and space) 3. Competition would lead to the death of some individuals while others would survive 4. Individuals that had advantageous variations are more likely to survive and reproduce. This process came to be known as Natural Selection The favorable variations are called Adaptations

Say in a species of blob, there exists blobs of all shapes and sizes (variation) Blobs eat the little purple organisms that live underground and on the surface.

During a particularly hot year, food became less abundant (competition), & blobs that had the ability to dig into the soil to get food had a better chance of survival. Many blobs died that year…….

The ones that survived mated and passed their genes to the next generation. (Reproduction)

The next generation had move blobs with the pointed noses The next generation had move blobs with the pointed noses. That is NATURAL SELECTION. Variation Competition Survival Reproduction

Comparing body structures Evidence of evolution can be found by comparing several kinds of data, including the fossil record, anatomical record, comparative embryology, and molecular record. Evolutionary theories are supported when several kinds of evidence support similar conclusions. 1.) Fossil record Shows change over time 2.) Anatomical record Comparing body structures Homologous, analogous, and vestigial structures 3.) Comparative Embryology Shows similar patterns of embryonic development in different species 4.) Molecular record Comparing protein & DNA sequences

Evidence of Evolution: Fossil Record Layers of rock contain fossils New layers cover older ones Creates a record over a long period of time Fossils show a series of organisms have lived on Earth

Evidence of Evolution: Fossil Record Transitional Species Fossils of transitional species show evidence of descent with modification Transitional Species: Considered “intermediate species” between an ancestor and its descendants Show slight structural changes as a particular species evolved, indicating that change is taking place over time

Evidence of Evolution: Fossil Record The Earth is old Life is old Life on Earth has changed

Evidence of Evolution: Anatomical Record Animals with different structures on the surface But when you look under the skin… It tells an evolutionary story of common ancestors

Evidence of Evolution: Anatomical Record The same bones under the skin But…limbs perform different functions, despite being built from the same bones Examples: Forelimbs of humans, cats, whales, & bats Same structure on the inside Same development in embryo Different functions on the outside Evidence of common ancestor Homologous structures have a COMMON evolutionary origin.

Evidence of Evolution: Anatomical Record Divergent Evolution In divergent evolution, related populations become less similar as they respond to different environments. Started with a common ancestor, so homologous structures are apparent But over time, each structure has evolved a different function

Evidence of Evolution: Anatomical Record But don’t be fooled by these… Analogous structures are similar in function but have different evolutionary origins.

Evidence of Evolution: Anatomical Record Analogous Structures Dolphins: Aquatic mammal Fish: Aquatic vertebrate Both adapted to life in the sea NOT closely related

Evidence of Evolution: Anatomical Record Flight evolved 3 separate times — evolving similar solutions to similar “problems” Convergent Evolution In convergent evolution, organisms that are not closely related resemble each other because they have responded to similar environments.

Evidence of Evolution: Anatomical Record Vestigial Structures A species with a vestigial structure probably shares ancestry with a species that has a functional form of the structure. Examples: Human tailbone Hind leg bones on whale fossils Why would whales have pelvis & leg bones if they were always sea creatures? Because they used to walk on land!

Evidence of Evolution: Anatomical Record Comparing Convergent and Divergent Evolution

Evidence of Evolution: Comparative Embryology Development of embryos tells an evolutionary story Similar structures during development Indicates a common ancestor All vertebrate embryos have a “gill pouch” at one stage of development

Evidence of Evolution: Comparative Embryology Human fetus at 8 weeks

Evidence of Evolution: Molecular Record When comparing the DNA of one species to another, more similarities are found in species that are more closely related. Similarity in the subunit sequences of biological molecules such as RNA, DNA, and proteins indicates a common evolutionary history. 10 20 30 40 50 60 70 80 90 100 110 120 Lamprey Frog Bird Dog Macaque Human 32 8 45 67 125 Compare common genes Compare common proteins Number of amino acids different from human hemoglobin

Building “Family Trees” (Cladograms) Closely related species are branches on the tree — Coming from a common ancestor Common ancestor to all these organisms on the tree

Interpreting “Family Trees” (Cladograms) Derived characters can be used to construct a cladogram, a diagram that shows the evolutionary relationships among a group of organisms. Common ancestor to all Organisms after a “derived character” all have that character in common, although their ancestor does not

Interpreting “Family Trees” (Cladograms) Organisms with a greater number of shared derived characters are more closely related Example: Primates and rodents & rabbits all have a vertebrate, bony skeleton, four limbs, an amniotic egg, and hair (5 shared characteristics)…so they are more closely related to each other than to amphibians, which only have a vertebrate, bony skeleton, and four limbs (3 shared characteristics)

Interpreting “Family Trees” (Cladograms) You Try: 1.) Which characteristics does a horse share in common with a dog? 2.) Which characteristics does a horse share in common with a lizard? 3.) Is a horse more closely related to a dog or a lizard? 4.) Which characteristic do all organisms on this cladogram share?

Artificial Selection How do we know natural selection can change a population? We can recreate a similar process “Evolution by human selection” The great variety of dog breeds is an example of artificial selection The environment (nature) is not selecting for traits in these organisms; humans are Humans are the ones breeding the dogs for traits that we think are desirable

Coevolution Coevolution: When two or more species influence each other’s adaptations and evolution 1.) The increasing occurrence of antibiotic resistance among bacteria is an example of coevolution in progress. Humans create antibiotics to fight bacteria, who in turn evolve to be resistant to the antibiotics 2.) Plants and insects (such as flowers and their pollinators) are another good example Insects rely on the pollen for food Plants rely on the insects to spread the pollen to allow for fertilization and reproduction