Evolutionary Theories - Lamarckism to Darwin's Voyage

The Theory of Evolution by Natural Selection

Evolution of Evolutionary thinking (Pre-Darwinian) Jean-Baptiste Lamarck (1744-1829) French naturalist, proposed a theory that organisms were driven by some inner force toward greater complexity. But thought that org. could pass on traits to their offspring that they acquired during their lives. ( Lamarckism , proposed in 1809)

Lamarckism Lamarck based his theory on two observations thought to be true in his day: 1. Use it or lose it - Individuals lose characteristics they do not require and develop those which are useful. 2. Inheritance of acquired traits - Individuals inherit the acquired traits of their ancestors.

Lamarckism Examples include: the stretching by giraffes to reach leaves leads to offspring with longer necks; Strengthening of muscles in a blacksmith's arm leads to sons with like muscular development. This theory was later disproved!

Darwins Voyage Charles Darwin Set sail on the HMS Beagle in 1831 Became the ship s naturalist Arrived in the Galapagos Islands in 1835 Observed that the animals on the islands were similar to those on the mainland

Darwins Voyage Galapagos Animals The Galapagos animals, while similar, were also different from island to island as well as to the mainland Most obvious difference were the sizes and shapes of the finches (small birds) beaks Sizes and shapes of the beaks were adapted to what the birds ate

Galpagos Finches Beak shape varies depending on diet Berr y eate r Seed eaters Cactus eaters Insec t eater s

Darwins Voyage On the Origin of Species (Darwin s book) For the 20 years that followed his return to England Darwin studied plants, animals and adaptations Darwin wrote about how species can change gradually over many, many generations and become better adapted to new environmental conditions.

Evolution "Change over time"

Natural Selection Organisms that are better adapted to an environment are more likely to survive and reproduce than organisms that are less well adapted.

Adaptations Katydids have camouflage to look like leaves. Non-poisonous king snakes mimic poisonous coral snakes.

Factors that affect Natural Selection: Overproduction most species produce far more offspring than will/can survive Competition: since food and resources are limited, the offspring have to compete to survive Variation: Members within a species exhibit individual differences these differences must be inheritable

How do new species form? Natural Selection-"survival of the fittest" Continental Drift-continents separated, the animals were separated Changes in environment-changes in water temp or acidity Mutations-changes in DNA Man-Artificial Selection (video from warm-up)

Mutations Some species are more susceptible to mutations. Some mutations allow the animal to survive; other mutations do not allow the animal to survive. The mutations that are not decrease the chance of survival remain.

Continental Drift Fossil records show that when the continents were connected animals walked across. When the continents separated, the animals were separated. Tectonics animation

Changes in the Environment Example, the pepper moth. Originally, the pepper moth was white, which was good because it could blend in. Then, trains were invented and the soot they produced covered the trees. Making the trees black. The moths that were black could now survive better.

Man: Artificial Selection Selective breeding as practiced by humans on domesticated plants and animals . For example: Dogs

Evidence of Evolution Fossil Record Similarities in Body Structure Similarities in Early Development Vestigial Structures Similarities in DNA

Fossil Record How fossils form An organism dies and becomes buried in sediment Minerals gradually replace the bones and more sediments cover the fossil Pterodactyl Trilobite

Homologous structures similar in function, similar in structure inherited from a common ancestor)

Analogous Structures similar in function, not inherited from a common ancestor. (Different in structure) Ex. bird wing butterfly wing

Vestigial Structures Vestigial Structures A structure found in an organism that is no longer in use but may have been useful at some point in the organism's life. Whales possess a femur and pelvis, but these bones are no longer useful to the mammals. Tail Present in human and all vertebrate embryos. In humans, the tail is reduced; most adults only have three to five tiny tail bones and, occasionally, a trace of a tail-extending muscle.

Similarities in Early Development Scientists look at embryos of different organisms and find that many embryos resemble one another.

Vestigial Structures Why do dogs have tiny, functionless toes on their feet (dewclaws)? Ancestral dogs had five toes on each foot

Similarities in DNA The more similar the sequences of DNA are, the more closely related the organisms are. Humans and chimpanzees DNA is more similar than human DNA is to dog DNA.

Patterns of Evolution Divergence Adaptive radiation Convergence

Divergent Evolution New species develop traits that differentiate them from their ancestors Divergence accounts for descendants that differ from their ancestors and from one another

Convergent Evolution Unrelated animals develop similar body forms to fill same niche

Adaptive radiation Mammals filled ecological niches vacated by dinosaurs Greatest mass extinction occurred millions of years before us- the dinosaurs More than 90% of all species died out the animals that remained filled the gap

How we know what happened when Radiometric Dating Stratigraphy Molecular clocks

Radiometric Dating Radioactive Dating (Absolute Dating) Rocks that fossils are found near contain radioactive elements. The half-life of a radioactive element is the time it takes for half the atoms in an element to change into a stable element (carbon 14 into carbon 12)

Stratigraphy Fossils from organisms that died longer ago are buried deeper in the sediment/rock than fossils from organisms that died more recently.

Molecular clocks When a stretch of DNA does indeed behave like a molecular clock, it becomes a powerful tool for estimating the dates of lineage- splitting events.