Chapter 14 Evolution: How Change Occurs

14-1 Developing a Theory of Evolution

Evolutionary Theory-a collection of carefully reasoned and tested hypotheses about how evolutionary change occurs

Lamarck idea 1: A desire to change

Lamarck idea 2: Use and Disuse

Lamarck idea 3: Passing on acquired traits

Lamarck thought that organisms change because they have an inborn urge to better themselves and become fit for their environments.

Example: Birds are able to fly because their ancestors desired to fly

Change occurred because organisms could alter their shape by using their bodies in new ways. He also believed that if an animal did not use a particular part of its body that body part would decrease in size and might disappear.

He believed they were inherited. That if an organisms acquired long arms it would pass those long arms on to its offspring

He was the first to devise a theory of evolution. He also brought it to the attention of other scientists

We are able to say that only genes are passed from parents to offspring not specific body structures.

Influence of Geology: Lyell’s Ideas

Influence of Farmers: Artificial Selection

Influence of Malthus: Population Controls

Artificial Selection Picking only individuals that allow traits that are wanted

Darwin believed that their was a process in nature that allowed only the organisms that were best suited with their environment to survive and reproduce

They are not able to all survive because there are not enough resources for all of them too. Most of them die in the first year after they are hatched

14-2 Evolution by Natural Selection

Natural Selection-Process in nature that results in the most fit organisms produce offspring

Animals compete for space

Animals compete for food

Animals compete for water

Individuals whose characteristics are well-suited to their environment survive. Individuals whose characteristics are not well-suited to their environment either die or leave fewer offspring Darwin Vs. Lamarck Video

14-3 Genetics and Evolutionary Theory What causes genetic variations? What do these variations have to do with evolution by natural selection? How are evolution, fitness, and adaptation described in genetic terms?

Genes: Units of Variation Genes allow for random variations which allows natural selection to happen Mutation and meiosis account for variations in genetics Organisms cannot control their DNA changing

Genetic Variations

Raw Material for Natural Selection Natural selection needs phenotypic variation to operate Look at all of the phenotypic variations in this class alone (height, weight, shapes of noses) Other organisms show this even though we don’t notice There are many differences between species

Phenotypic Variation

Evolution as Genetic Change Biologists study groups of organisms called populations Population-a collection of individuals of the same species in a given area whose members can breed with one another Example: all the fishes of a certain species in a single pond is one population

Because all of a population can interbreed, they share a common group of genes called a gene pool Gene pool contains a specific amount of alleles for each trait The number of times an allele occurs in a gene pool compared with the number of times other alleles for the same gene occur is called the relative frequency of the allele

Gene Pool

Sexual reproduction alone doesn’t change relative frequency in a population Its similar to shuffling a deck of cards, many combinations but doesn’t change the number of aces, kings, etc… Evolution is any change in the relative frequencies of alleles in the gene pool of a population In other words the number of alleles have to change for a gene pool to change

Genes, Fitness, and Adaptation Genes get passed to offspring when organisms reproduce Evolutionary fitness is the success an organism has in passing its genes to the next generation An adaptation is any genetically controlled characteristic that increases an organisms fitness

Example: if a weight lifter exercises a lot and gets large muscles they do not pass that on to their offspring If they have a gene which makes it easier for them to gain muscles then that can get passed on to their children

A Genetic Definition for Species A species is a groups of similar-looking organisms that breed with one another and produce fertile offspring Members of a species share a common gene pool If there is a genetic change it can pass through the gene pool If it increases fitness the gene will eventually be found in many individuals This means species evolve together

14-4 The Development of New Species What is a niche? How do new species develop from existing species? What are the results of divergent evolution? Of convergent evolution?

The development of New Species Speciation-the process of new species being created

The Niche: How to Male a Living Organisms need to acquire the necessities of life (food, water, space) The combination of what an organism does and the place in which it occupies is its niche (example: work place) If two species share the same niche they compete for resources there, one species will not survive

No two species can occupy the same niche in the same location for a long period of time One of the species will be more efficient than the other which will allow them to survive and reproduce Any species that occupies an unoccupied niche they will be better able to survive This can lead to new species

The Process of Speciation New species usually form only when population are isolated, or separated (remember gene pool and definition of a species) This separation of populations so that they do not interbreed to produce fertile offspring is called reproductive isolation

Reproductive isolation is a reason for the formation of new species May result from geographical barriers which can change ways in which organisms breed One isolation occurs natural selection increases differences between populations This then alters the genes of isolated species resulting in new species

Darwin’s Finches: An Example of speciation Finches in the galapogos were examined Darwin felt that 13 species evolved and are different due to geographical barriers and reproductive isolation This caused 1 species to evolve into 12 Video

Darwin’s Finches

Speciation and Adaptive Radiation Adaptive Radiation-when one species gives rise to many Also known as divergent evolution During a period of adaptive radiation, organisms evolve characteristics that enable them to survive in their niches

Adaptive radiations among different organisms often produce species similar in appearance and behavior This is known as convergent evolution This has produced many of the analogous structures in organisms today These are similar in appearance and function, but they have different origins

Convergent Evolution

Analogous Structures

Analogous structures usually have very different internal structures Example: Wings

14-5 Evolutionary Theory Evolves

Natural selection is not always necessary for genetic change to occur. Gene pools can change, evolution can occur in the absence of natural selection. Chance plays a larger part

Genetic Drift-Random change in the frequency of a gene

Genetic drift alters the frequency of alleles in a gene pool. Can happen by a natural disaster or anything randomly. Usually causes a less popular allele to become more popular

All characteristics of an organism do not have to contribute to its fitness. The rhinos from India have one horn and the rhinos from Africa have two horns. It is not clear whether having two horns or one horn increases fitness.

If the species is well adapted to its environment which doesn’t change and if there is not competition against the species the gene pool may not be altered

Gradualism- the theory that evolutionary change occurs slowly and gradually

State of equilibrium: It means that the organisms did not change very much when they existed

First, a small population of a species could become isolated. In small populations, genetic changes can spread more rapidly.

Second, a group of organisms might migrate to a new environment, where they could rapidly evolve to fill available niches.

Third, the environment could change dramatically and cause a mass extinction. Such an event would open up niches for the surviving organisms

After mass extinctions there are many empty niches, and these niches can be filled through adaptive radiations

Punctuated Equilibria-The theory states that evolution occurs when long periods of relatively little change are interrupted, or punctuated, by brief periods of rapid change.