Chapter 10 Darwin's Theory of Evolution

Voyage of the Beagle Charles Darwin – Naturalist (1809-1882) 1831 – set sail on the H.M.S. Beagle

The Galápagos Islands 1000 km west of South America Islands are close together but very different Darwin was fascinated by the land tortoises and marine iguanas

Galapagos Islands -Darwin collected animal specimens on the four islands he visited. He noticed each island had their own varieties of animals. The animals he saw were different than those in Europe but similar to those in South America. He realized that there is a huge amount of diversity in animal and plant life.

The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

Artificial Selection Later, Darwin thought about how pigeon breeders “selected for” traits that they wanted in the offspring. He called this artificial selection. Can you think of some examples of how we use it today? Darwin wondered if this could happen in nature.

Natural Selection 1. There is variation in species. The Four Principles of Natural Selection 1. There is variation in species. 2. Variations can be inherited. 3. Individuals have more offspring than can survive on available resources. 4. Traits that increase survival are more likely to be passed on (remember the fast rabbit we talked about last chapter)

Natural Selection Darwin thought that, given enough time, natural selection could change a population enough to create a new species.

Other Ideas Lamarck thought that animals could pass on body and behavior characteristics that they acquired throughout their lives

Darwin realized that natural selection worked with traits that animals already had, not characteristics they had gained throughout their lives or experiences they had.

Evolution When Darwin wrote a book about his findings he only used the word “evolution” on the last page. Evolution – cumulative changes in groups of organisms through time. Evolution is driven by natural selection. Natural Selection explains how evolution works Populations evolve, but individuals do not

Evidence of Evolution The theory of evolution states that all life on earth descended from a common ancestor. Fossils provide some of the best evidence for evolutionary change

The Fossil Record Some ancient species have modern counterparts

Fossil record of the camel

Comparative Anatomy These are all forelimbs. What do they have in common?

Homologous Structures Homologous structures- anatomically similar structures that are inherited by a common ancestor Example: forelimbs have very similar bones in many animals

Vestigial Features Reduced forms of structures found in other organisms. Examples: human appendix, wisdom teeth, pelvic bones in snakes, and lots more… As an embryo you even had the beginnings of gills.

You don’t need your appendix, but it is extremely important for some animals.

Human tailbone is a vestigial vertebrate tail consists of fused vertebrae that no longer function as a tail

Comparative Embryology Embryos from different species have similarities. Example: many embryos that don’t live in the water (including us) have pharyngeal slits that develop into gills in fish.

Similarities In Embryonic Development Evidence for Evolution - Comparative Embryology Similarities In Embryonic Development

Adaptation A trait shaped by natural selection to increase the survival or reproductive success of an organism.

Camouflage An adaptation that helps an organism blend in to the environment

Mimicry A adaptation in which one species evolves to resemble another

Allelic Frequencies Populations change with the frequencies of alleles change. Genetic drift-a change in allelic frequencies in a population due to chance.

Hardy-Weinberg Principle When allelic frequencies remain constant, a population is in genetic equilibrium. The principle says that evolution won’t occur unless a population is acted on by some force.

Hardy-Weinberg Equation p2+2pq+q2=1 This equation helps us understand the frequencies of alleles. But, this equation doesn’t really describe what happens in nature (we know allelic frequencies change)

Why the Equation Cannot Describe Real Populations -gene flow (new individuals come in, some leave -nonrandom mating (mating is rarely completely random) -Mutations (mutations change gene frequencies) -Natural Selection (individuals aren’t equally adapted, we know natural selection changes allelic frequencies.

Founder Effect Occurs when a small sample of a population gets isolated. How would the continuing population change? What kind of environment could cause this? Think back to the places Darwin studied

Bottleneck A bottleneck occurs when a population declines to a very low number and then rebounds.

Sexual selection Change in frequency of a trait based on competition for a mate Darwin wondered why individuals would pick mates based on traits that did not seem to enhance survival.

Reproductive Isolation Speciation-the process by which some individuals change so much that they cannot produce reproductively viable offspring.

Even though these are both birds, they are different species Even though these are both birds, they are different species. Some species don’t breed with one another for various reasons. Can you think of some?

Some species can reproduce, but some offspring cannot reproduce Some species can reproduce, but some offspring cannot reproduce. Example: Ligers and mules

Zebra-donkey hybrid

Two Types of Speciation Allopatric speciation-a physical barrier separates one population into two or more. Sympatric speciation- a species evolves into a new species without a physical barrier

Abert Squirel Kaibab Squirel The grand canyon separates these two squirrel species, so they are never in contact with one another. Is this allopatric or sympatric speciation?

One species of apple flies only feeds one kind of apple why the other eats only another kind. However, they live side by side. Sympatric or allopatric? There is no physical barrier between these flys

Coevolution When two species live in close relationship with one another, the evolution of one species affects the evolution of another.

Gradualism Remember, most of the time evolutionary changes happen in very small steps over millions of years. Scientists call this idea the theory of gradualism