Darwin’s Theory of EvolutionCh. 29

Evolution

• Evolution means change over time

• A scientific theory is NOT just a belief, it is a well-supported tested explanation.

Darwin

• In 1831 Darwin sets sail on the HMS Beagle.

• In 1844 he writes his theory on the origin of species.

• In 1858, Darwin and Wallace publish their theories on evolution.

• Evolution means change over time.

History of Darwin’s Studies• Darwin went on an around-

the-world trip on the HMS Beagle and traveled to the Galapagos Islands.

• He particularly liked and observed the finches. He also observed the tortoises on different islands.

• He observed each different group had its own niche.

• He studied 13 different species and saw how they adapted to their environment.

Fossils

• A fossil is the preserved remains or imprints of ancient organisms.

• Someone who studies fossils is called a paleontologist.

• Fossils are found in sedimentary rock formed when sand and silt settle to the bottom of water.

• Not all animals turn are fossilized, why?

• Do you think we have a complete fossil record?

Determining ages of Fossils

• Relative dating-– Looks at the layer of

the earth they are found.

– The oldest fossils will be deeper.

• Radioactive dating– Determined by

remaining radioactive isotopes the fossil contains.

Tracking Changes

• According to evolutionary theory, all life originated from a common unicellular ancestor through natural selection.

• Scientists use radioactive dating to calculate fossil’s age.

• The phylogeny (or evolutionary tree), is not linear, it branches and stops and some of it is incomplete.

An Ancient, Changing Earth

• In 1785 James Hutton proposed the Earth is shaped by geological forces that took place over extremely long periods of time. He estimated the earth is millions, not thousands of years old.

• Charles Lyell agreed and wrote a book in 1833 the explained the shaping of Earth’s geological features.

• He gave his book to Darwin before Darwin set sail.

Popular Belief

• Prior to the studies of Charles Darwin, the most widespread belief was that all known species were created at the same time and remained unchanged throughout history.

• Some scientists at the time believed that features an individual acquired during a lifetime could be passed onto its offspring, and the species could gradually change to fit an environment better.

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Lamark• In 1809 Jean-Baptiste

Lamarke hypothesized that “simple” organisms emerge spontaneously and evolve to greater “complexity”.

• Lamark’s hypothesis about acquired characteristics was disproved by Weisman, who concluded that changes in an individual during a lifetime do not affect its offspring.

• 3 principles to his theory:1. Organisms constantly strive

to improve themselves.

2. Most used body structures develop and unused waste away.

3. A structure is modified by use or disuse, the modification is inherited to the offspring. (Inheritance of acquired characteristics.)

Darwin’s Arguments

• Darwin argued that only biologically inherited characteristics were advantageous in surviving and reproducing. The offspring would also inherit and pass on those advantages, and over generations the aggregation of these inherited advantages would lead to new species.

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Population Growth

• In 1798 Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.

• Do you agree of disagree with Malthus?

Population Control

• Darwin read Malthus’ work reasoned that there is always competition for food, water and space in the environment. The individuals that survive the competition can then reproduce.

Origin of Species

• Darwin’s book, published in 1859, was a quick success. It came from the clear and understandable argument that natural selection and selective breeding of animals was in wide use at the time. There was a massive array of biological and fossil evidence to support the argument.

• Selective breeding: breeding of organisms to produce certain desired traits in their offspring.

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Variation

• A species consists of interbreeding populations organisms that produce healthy offspring.

• Within a species there is much variation or differences between members of a population.

• Give an example of variation among a species.

Variation

• Variation can be dramatic or subtle.

• Examples of how organisms may vary:– Fur color

– Shape of teeth

– Size

– Markings

– Biochemically

– Eye color

Other things that cause VariationInherited variation:

1. Mutation

2. Recombination

• Most mutations are either neutral or harmful, sometimes they may increase the chance for survival, esp. when the environment is changing.

• Ie. Silver colored red fox in a snowy environment.

Altered genes may be passed on to every cell that develops from it. This may help, harm, or have little or no effect on the offspring’s success in the environment.

Biodiversity• In communities

populations of organisms live to together, interact, and often compete for natural resources. These communities include a collection of niches. The variety and abundance of species that make up a biological community is called biodiversity.

• There are between 5 and 30 million different species.

• 99% of all organisms that ever lived are now extinct.

Biodiversity is Good

• The great diversity of species increases the chance that at least some living things will survive in the face of the large changes in the environment.

• Genetic recombination allows for a greater diversity.

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Niches

• Through adaptation, populations often become suited to a specific niche.

• Niche- habitat and the role of a population plays in that habitat.

• It includes:– Where organisms live

– What and how they eat

– How they raise their offspring

– What their predators are

– Space

– Light

– Moisture

– Temperature

Adaptation

• An adaptation is an inherited trait that increases a population’s chance of survival and reproduction in a particular environment.

• What are some ways that you know animals have adapted to their environment?

• The ability of an individual to survive and reproduce in its specific environment is fitness.

Survival of the Fittest

• Individuals that are best suited to an environment (adaptations that enable fitness) survive and reproduce most successfully.

• Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species fitness in its environment.

Natural Selection• 4 Main Points.

1. There is variation with a population.

2. Some variations are favorable.

3. Not all young produced in each generation survive.

4. Individuals that survive and reproduce are those with favorable variations.

5. Descent with Modification

Ostriches are the fasted birds on land due to favorable traits such as long, powerful legs.1.31

Natural Selection Tutorial

Natural Selection

• Natural Selection leads to organisms that are well suited in particular environments.

• It provides a scientific explanation for the history of life on Earth as depicted in the fossil record and similarities evident within the diversity of existing organisms.

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Descent with Modification

• Over time, natural selection produces organisms that have different structure, establish different niches, or occupy different habitats. As a result, they look different from their ancestors.

• What do you think the common ancestor to tigers, panthers and cheetahs looked like?

• Common descent- all living and extinct organisms were derived from a common ancestor.

Structures

• Homologous Structures- traits that are similar in different species because the species share a common ancestor.Ie. Arm, fin and wing may have evolved from the forelimb of a common vertebrate.

Exploring Evolution

• Vestigial Structures- inherited, but reduced in size and often unused.Ie. Pythons have hip and leg bones.

Analogous structures- those that are similar in function, but are not inherited from a common ancestor.Ie. Insect and Bird Wings

DNA history

• Scientists rely on embryology and biochemistry to understand evolution.

• Gill pouches in all vertebrates.

• Embryology is the study of the early stages of an organisms development.

• Biochemists study and compare chemicals found in living things.

Evidence of Evolution

• Darwin argued that living things have been evolving on Earth for millions of years.

• 1. Fossil Record- layers of earth• 2 Geographical distribution of

living species- similar animals in different locations were the product of different lines of evolutionary descent.

• 3. Homologous structures• 4. Similarities in early

development (embryology)

Evolution of Populations

Genetic Variation

• The more genetic variation within a population, the better chance it has to survive.

• Why?

• 2 sources– Mutations– Genetic recombination

during meiosis

Crossing over

Population Genetics

• Gene pool- all the combined genetic material of all of the members of a given population.

• Allele frequency- the number of each allele is a fraction of all of the genes for a particular trait. (pg. 394)

In genetic terms, evolution is any change in the allele frequency (relative frequency) of alleles in a population

• Sexual reproduction can produce many different phenotypes, but it does not change the relative frequency of alleles in a population. Think of deck of cards.

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generations

In any population, but especially small populations, allele frequencies change over time by chance.

An allele frequency graph

Single Gene and Polygenic Traits

• Single gene trait is controlled by one gene– Widows peak

– Freckles

– Dimples

– Roll tongue

– Taste PTC

• Polygenic traits are controlled by many genes.– Body stature

– Eye color

– Height

Natural Selection on Single Gene Traits

• Natural Selection on Single Gene traits can lead to changes in allele frequencies…evolution.

• Organisms of one color, may produce fewer offspring than organisms of other colors.

Natural Selection on Polygenic Traits

• Natural selection can affect the distributions of phenotypes in 3 ways.

1. Directional selection

2. Disruptive selection

3. Stabilizing selection

Directional and Disruptive Selection

• Directional Selection occurs when a change in the environment favors an extreme phenotype.

• What is a phenotype and what are some examples?

• Ie. Peppered moth

• Disruptive selection occurs when an environmental change makes it unfavorable to have a medium phenotype. You need an extreme one.

Note: Berkley did an experiment and found the conditions for the moth example, wasn’t 100% the way perceived.

Testing Natural Selection in Nature

• Rosemary and Peter Grant visited the Galapagos Islands and did not see the different finches competing or eating different foods. During the rainy season, there is plenty of food and finches are able to eat anything. In the dry season drought, food becomes scarce and differences in beak size can mean the difference between life and death. What time of selection is this?

• Directional

Directional Selection ExampleDirectional selection favors those individuals who have extreme variations in traits within a population. A useful example can be found in the breeding of the greyhound dog. Early breeders were interested in dog with the greatest speed. They carefully selected from a group of hounds those who ran the fastest. From their offspring, the greyhound breeders again selected those dogs who ran the fastest. By continuing this selection for those dogs who ran faster than most of the hound dog population, they gradually produced a dog who could run up to 64km/h (40mph). The greyhound was originally used to hunt the fastest of game, fox and deer. Their bred dates to Egypt in 3BC.

Maintaining Genetic Equilibrium

• 5 conditions:

1. No natural selection

2. Random mating

3. No migration

4. No significant mutations.

5. Very large population

Hardy-Weinberg Tutorial

Genetic Drift• Genetic Drift is the random

change in allele frequencies in a population due to chance events, such as natural disasters or migration. (Would genetic drift have a greater impact on smaller or larger populations?)

Ex. Florida Panther- hunted-less genetic variation- Texas cougars introduced

• “Bottlenecking” is when genetic drift occurs after a random population reducing event.

• The more variation, the easier it is to survive because they can adapt better.

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Founder effect

• Allele freq. change as a result of the migration of a small subgroup of population.

• Will the new population become different or more like the parent population?

• Due to chance

• Ex: Hawaiian Fruit Flies

Genetic Drift

Let’s show how you get the allele frequencies.

An example is the Cheetah.

Speciation

• Speciation is the evolution of one or more species from a single ancestor species.

• It can occur when members of a population become isolated from each other. (possibly from earthquakes.)

• Once two populations are reproductively isolated, they are considered separate species.

Allopatric Speciation

• Aka. Geographical Isolation

• Physical barrier ( continental

split, rise in sea level, formation

of mountain range, advance of

glacier, change in habitiat)

prevents gene flow between

populations of a species

– Archipelago hotbed of speciation

Allopatric Speciation

Allopatric Speciation in the Grand Canyon

Behavioral Isolation

• Two populations are capable of interbreeding, but have differences in courtship rituals or other reproductive strategies.

Temporal Isolation

• Two or more species reproduce at different times.

• Orchid releasing pollens on different days, they can’t pollinate each other.

Speciation in Darwin’s Finches

• Speciation in the Galapagos finches occurred by:

• 1. Founding of a new population.

• Geographic isolation• Changes in new

population’s gene pool• Reproductive isolation• Ecological

competition

2 major extinctions

• Cretaceous- more than half of all existing species wiped out. (Dino’s)

• 65 mya

• Permian- reduced the number of species by 90%.

• 250 mya during Pangea- less water habitat.

Evolution does not occur in a set direction

• Evolution builds on what already exists, so the more variety there is, the more there can be in the future.

• However, evolution does not necessitate long-term progress in a set direction.

Rate of Evolution

• Gradualism- theory that new species evolve as the genomes of two populations differentiate over enormous spans of time.

(Small genetic changes occur slowly within a population.)

• Punctuated equilibrium- theory that populations remain genetically stable for long period of time, interrupted by brief periods of repaid genetic change.

• Rapid genetic changes in a population can result in the evolution of new species.

Graduated vs. Punctual

Mechanisms of Evolution

• Divergent Evolution- when isolated populations of a species evolve independently. It occurs when geographic barriers separate population members or when a small group leaves an original population.

• Ex: polar bears and brown bears

• Convergent Evolution-occurs when natural selection has produced analogous adaptations in response to similar environment between different species. Ie. Maned Wolf and Serval Cat

Eat same, legs same, ears same.

Coevolution

• Species that interact closely often adapt to one another in a process called coevolution.

• What does the prefix co- mean?

• Ex:– Predatory birds and

mimicry of butterflies– Parasites and hosts– Plant-eating animals

and the plants they eat– Plants and the animals

that pollinate them.

Adaptive Radiation

Adaptive Radiation is the evolution of many diversely adapted species from one common ancestor. It usually occurs on an isolated island.

ie. Finches that Darwin studied all came from common ancestor, but had different beaks for the kind of food they ate.

What differences do you see between the tree finches and ground finches? Why?

Patterns of Evolution

Which is adaptive radiation, divergent, convergent, and parallel evolution?

Parent Species

Why is understanding evolution important?

• Drug resistance to viruses and bacteria

• Pesticide resistance

• Selective Breeding

• Others?

• How do each of these effect you?