The Theory of Evolution by Natural Selection

Introduction Evolution – includes all of the changes in the characteristics and diversity of life that occur throughout time. Evolution can occur on both large and small scales. Microevolution Macroevolution

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: “Use it or lose it” - Individuals lose characteristics they do not require and develop those which are useful. Inheritance of acquired traits - Individuals inherit the acquired traits of their ancestors.

This theory was later disproved! 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!

Darwin’s 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

Darwin’s 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

Galápagos Finches Beak shape varies depending on diet Berry eater Seed eaters Cactus eaters Insect eaters

Darwin’s 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 The gradual change in a species 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 Overproducers Producers mature rapidly  mature slowly short-lived: most die before they reproduce live long lives: low juvenile mortality rate  have many offspring - tend to overproduce have few offspring at a time invest little in individual youngsters  care for their young population not regulated by density: boom and bust population figures population stabilizes near carrying capacity

Factors that affect Natural Selection: Competition: since food and resources are limited, the offspring have to compete to survive Darwin called it: “Struggle for existence”

Factors that affect Natural Selection: Variation: Members within a species exhibit individual differences – these differences must be inheritable Natural selection won’t work in a population of clones! Remember that a key to variation is sexual reproduction.

Natural Selection In any population of organisms there is natural variation. Some of these variations will allow the organisms possessing them to survive and reproduce better than those without these particular traits.

Factors that affect Natural Selection: Survival to reproduce: Only those individuals that are better suited to the environment will survive and reproduce (“Survival of the fittest”). Fit individuals pass on to a portion of their offspring the advantageous characteristics.

How do new species form? Natural Selection Continental Drift Changes in environment Mutations Man

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

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.

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.

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

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

Similarities in Body Structure “Homologous structures” If the two organisms have body structures that are similar, they must have had a common ancestor.

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

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.

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.