Chapter 121 -- Part 1: Historical Context for Evolutionary Theory
The ancient world was influenced by the theories of Aristotle.
All life forms can be arranged on a ladder of increasing complexity, each with its own rung.
The species do not change.
Humans are at the top of the ladder.
Taxonomy is the branch of biology concerned with naming and classifying the diverse forms of life.
He believed that a classification system would reveal a divine plan.
The naming system used today was developed by him.
Every organisms name consists of two parts, a genera name and a species name.
The scientific name of humans is Homo sapiens.
The man who died before Darwin published his thesis studied fossils and realized that the Earth is made of different fossils.
He believed that a series of events in the past were caused by mechanisms different from those in the present.
The changes in life on Earth were caused by these events.
Cuvier's study of fossils was very important in the development of Darwin's theory.
One of the most influential geologists of his day, James Hutton, published his theory of gradualism in 1795.
He said that Earth had been molded by gradual change.
The forces of wind, weather, and the flow of water that he saw in his lifetime were the same ones that formed the various geological features on Earth.
His theories were important because they were based on the idea that Earth had a long history and that change is normal.
Darwin's era had a leader in the field of geology.
Slow, continuous actions result in geological change.
He believed that the Earth was older than 6,000 years old.
The Principles of Geology was an influence on Darwin.
Lamarck developed a theory of evolution.
The year Darwin was born, he published his theory.
His theory is based on the idea of inheritance of acquired characteristics.
He said that organisms change in response to their environment.
According to Lamarck, the giraffe developed a long neck because it ate leaves from a tall tree for food.
The animals stretched their neck and passed on the trait to their offspring.
The theory was widely accepted in the early 19th century.
Alfred Russell Wallace wrote an essay about the process of natural selection that was similar to Darwin's work, which had not yet been published.
When he was 22 years old, Charles Darwin left England to visit the Galapagos Islands, South America, Africa, and Australia.
Darwin's theory of natural selection or descent with modification as the mechanism for how populations evolve was not published.
Maybe he was afraid of what his theories would do.
He published " On the Origin of Species" in 1859 after seeing a similar book by Wallace.
The traditional view of a young Earth inhabited by unchanging species was challenged by Darwin's theory.
Natural selection is a major mechanism of evolution.
reproductive success is a measure of evolution.
Populations tend to grow fast and overpopulated.
Malthus's work on population growth, disease, and famine was published in 1798.
There is variation in the ability of individuals to survive and reproduce.
The origin of variation in a population could not be explained by Darwin.
Only the best-fit individuals survive and get to pass on their genes to their offspring.
Evolution occurs when a population has certain beneficial qualities.
According to Darwin's theory, giraffes were short-necked and had different neck lengths.
The taller people had a better chance of surviving as the population of animals increased.
Until long-necked giraffes existed, the proportion of giraffes in the population with longer necks increased.
The insects don't become resistant to pesticides.
Some insects are resistant to a particular chemical.
The resistant insects have an advantage when the environment is sprayed.
The insects that are not resistant to the insecticide die and the remaining resistant ones breed quickly.
The new population is resistant to pesticides.
Natural selection toward resistance to insecticides is an example of directional selection.
At times of ecological stress, species extinction rates are rapid.
Natural selection can change the frequencies of inherited traits in a population in five different ways.
Five types of selection are stabilizing, disruptive or di versifying, directional, sexual, and artificial.
You should be able to describe a model that represents evolution.
Stabilizing selection eliminates the extremes and favors the more common intermediate forms.
Many forms are weeded out in this way.
The majority of birth weights are in the 3-6 pound range.
Infant mortality is higher for smaller and larger babies.
Young birds of the same species that lay a smaller number of eggs will have a larger clutch size than birds of the same type that lay a larger number of eggs.
Extreme types are increased in a population at the expense of intermediate forms.
A balanced polymorphism is when one population is divided into two or more different types.
The formation of two new species may be a result of disruptive selection.
Imagine that an environment with light rocks and dark soil is colonized by light, intermediate-colored, and dark mice.
The frequencies of camouflaged and dark mice would increase, while the intermediate-colored mice would die out.
Changing environmental conditions can lead to directional selection, where one phenotype replaces another in the gene pool.
There are two examples.
Biston betularia is an example of industrial melanism.
In England until 1845, most were light, but a few were dark.
Smoke and soot polluted the environment, making all the plants and rocks dark.
Only a few light-colored individuals could be found in the industrialized regions by 1900.
White and dark moths were easy prey for predator before the industrial revolution.
After the environment was darkened by pollution, dark moths were camouflaged and had an advantage.
The population of light moths was replaced by dark moths.
Rapid shifts in allelic frequencies can be produced by directional selection.
The discovery of antibiotics led to the emergence ofbacteria that were resistant to the drugs.
Scientists now know that the genes for antibiotic resistance are carried on small DNA molecule called plasmids, which can be transferred from one cell to another and which can spread the resistance very rapidly within the population.
The appearance of antibiotics does not cause resistance because it selects against the susceptible ones.
The next generation will be resistant since only resistant individuals survive to reproduce.
The experiment carried out by Joshua Lederberg proved that somebacteria are resistant to antibiotics.
Secondary sexual characteristics are related to competing for and attracting mates.
The evolution of horns, antlers, large stature, and great strength in males are the result of sexual selection.
The harem may consist of as many as fifty females.
Long canines are important for male-male competition in baboons.
Sexual dimorphism is the difference in appearance between males and females.
Birds colored in a way to blend in with their surroundings are more likely to protect their young.
The males have bright colors because they must compete for the attention of females.
The fitness of an organisms or a population can be increased or decreased by certain types of variation.
Humans breed plants and animals by looking for individuals with desired characteristics.
This is called artificial selection.
Racing horses and laying hens are bred to produce larger eggs.
Humans have bred a lot of vegetables from the wild mustard plant.
In order for a population to evolve as the environment changes, there needs to be variation in a population.
Darwin knew that variation exists in every population.
There are hundreds of breeds of dogs.
Canus familiaris is one species of dog.
Natural selection is thought to reduce genetic variation by removing unfavorable genotypes from a population.
There are eight mechanisms that preserve diversity or variation in a gene pool or population.
There are two or more distinct forms of a trait in a single population of a species.
The land snail's shells have a wide range of colors and patterns.
Banded snails are less visible than unbanded ones and therefore are less preyed upon.
Unbanded snails have an advantage in areas where the background is uniform.
Both varieties continue to exist despite the fact that each morph is better adapted in a different area.
There are two different types of rabbit in North America.
Rabbits in the cold, snowy north have short ears to conserve body heat.
Rabbits with long ears and mottled fur blend in with the surrounding woodsy areas to reduce body heat.
A graded variation in the phenotype of an organisms is known as a cline.
This is an example of a north-south cline because of the differences in rabbit appearance.
Sexual reproduction provides variation due to the shuffling of alleles.
During meiosis I, the exchange of genetic material of homologous chromosomes occurs.
The genes from two parents are combined to create individual chromosomes.
There are two or three events per pair in humans.
There are organisms that are not closely related that are outbreeding.
It is the opposite of inbreeding.
A strong genes pool and variation within a species are maintained by outbreeding.
If organisms that are closely related interbreed, they tend to have bad effects on the genes.
There are many mechanisms that promote outbreeding.
The dominant male of a pride chases away the maturing males before they become sexually mature.
This makes sure that the young males don't mix with their female siblings.
The young males are looking for another pride to join.
If one of these young male lions succeeds in overthrowing the king of another pride, he will inseminate all the females of that new pride and develop his own line.
When conditions change in the future, Diploidy could be an advantage because it hides a huge pool of alleles that may be harmful in the present environment.
Heterozygote keeps advantage in a population.
The hybrid individual is selected for this phenomenon because it has more reproductive success.
The hybrid is better adapted than the Homozygotes.
Heterozygote advantage is defined in terms of genetics.
People who are hybrid for the sickle cell trait have an advantage over other people.
Those who are hybrid have normal hemoglobin.
They are resistant to Malaria, which is endemic in West Africa.
People who have a genetic condition called the ss are at a disadvantage because they may die of the disease.
Some people with normal hemoglobin are not at risk of having sickle cell disease, but they are at risk of dying from Malaria.
The sickle cell trait is retained in the genes.
The minority advantage is a mechanism that preserves variety in a population.
This increases the frequencies of the less common ones and decreases the frequencies of the more common ones.
In predator-prey relationships, a standard representation of prey is developed that allows them to hunt a particular kind of prey effectively.
If the prey individuals are different, the most common type will be preyed upon more often than the less common type.
These rare individuals will become more common for a while, will lose their advantage, and eventually will be selected against.
Evolutionary neutral trait seem to have no advantage.
There are different blood types in humans.
Scientists don't know why they have remained in the human population.
It is possible that they influence survival and reproductive success in ways that are difficult to measure.
The agents of change for a population are genetic drift, nonrandom mating, and natural selection.
Genetic drift is caused by chance.
It is a constant change in the alleles from one generation to the next.
It limits diversity.
The founder effect is one of the two examples.
Small populations can be affected by chance and random events.
Natural disasters, such as fires, earthquakes, and floods, reduce the size of a population, resulting in a loss of genetic variation.
The resulting population is much smaller than the original one.
Some alleles may be overrepresented compared to the original population.
The bottleneck effect is what it is.
There are two examples.
The high rate of Tay-Sachs disease among Eastern European Jews is due to a population problem experienced by Jews in the Middle Ages.
Many Jews were killed and the population was reduced to a small fraction of its original size during that period.
A disproportionate percentage of people who remained alive had the Tay-Sachs gene.
The incidence of the trait remained high because Jews in Europe remained isolated and did not intermarry with other Europeans.
The northern elephant seal was almost wiped out during the 19th century.
Since 1884, when the seal was placed under government protection, the population has increased to about 35,000, all descendants of the original group.
The founder effect is when a small population breaks away from a larger one to colonize a new area.
It is possible that rare alleles may be overrepresented.
The founder effect occurred in the Old Order Amish of Lancaster, Pennsylvania.
A small group of settlers from Germany came to the United States in the 17th century.
One or more of the settlers had extra fingers and toes.
The population has a high incidence of polydactyly due to the extreme isolation and intermarriage of the close community.
If a trait is dominant or recessive, it simply determines if it is expressed or hidden.
The trait is not determined by how common it is in a population.
Genetics can cause an increase or decrease in allelic frequencies of a trait.
Gene flow is the movement of all genes into or out of a population.
It can happen as a result of the migration of fertile individuals.
The wind can carry pollen from one valley to another.
Gene flow increases diversity.
Evolutionary change occurs when there are changes in genetic material.
They make us more diverse.
A new allele can be introduced into a population.
The cumulative effect of all the genes in a population can be significant.
Individuals pick their mates for a specific reason.
The less-fit individuals are eliminated by the selection of a mate.
There are two types of snow geese: white and blue.
White geese tend to mate with blue geese.
If blue geese became more attractive and both blue and white geese began to mate with only blue geese, the population would evolve quickly and favor blue geese.
Natural selection is the main mechanism of evolution.
People who are better adapted to a particular environment have better reproductive success.
They pass their genes on to more offspring.
A stable, nonevolving population is one in which allelic frequencies don't change.
In 1,000 years, if the population is not evolving, the allele will be the same as it is now.
A small change in the gene pool will be mitigated by the large number of people in the population.
There must be no migration of organisms into or out of the pool.
A change in allelic frequencies could be caused by a change in the gene pool.
Those who are better adapted will have a reproductive advantage and the population will evolve.
The equation allows us to calculate frequencies of alleles.
Although it can be applied to complex situations of inheritance, for the purpose of explanation, we will discuss a simple case.
The letter q and the letter p are used by scientists to indicate the frequencies of the dominant and recessive alleles.
The basis for this equation is the mono hybrid cross.
You can use your calculator on the exam in 2020.
The principle is the same even if the problems are not simple.
There are three sample problems.
The blue eyes have a trait that is represented by q 2.
The square root of 0.09 is the solution for q.
If q is less than 0.3, then p is 0.7.
The brown condition is represented by 2 pq.
Substitute values for 2( p )( q ) for the percent of the population that is hybrid.
The percentage of the population that is brown is 42%.
The dominant is represented by p 2.
The percentage of the population that is brown is more than 50%.
The square root of 0.09 is not 0.03.
The percent of the population that is dominant if it's a combination of both genders.
q 2 is 16. q 2 is calculated as.16 and q is calculated as 0.4.
The percentage of the population that is dominant is.36.
The population's allele may change.
The percent of the population that is hybrid is determined by the allelic frequency of the trait.
The value of q is not q 2.
To get the value of p, you need to subtract from 1.
If p + q is 1 and q is 0.5, then p + 0.5 is 1.
The percentage of the population that is hybrid is 50% if both p and q are used.
A species is a group of people who have the potential to interbreed in nature and produce offspring.
In captivity, lions and tigers can be bred but not naturally.
They are considered separate species.
A mule that is not fertile can be produced by horses and donkeys.
The horse and donkey are different species.
A species is defined in terms of reproductive isolation, meaning that one group of genes becomes isolated from another to begin a separate evolutionary history.
Under the pressure of different forces in different environments, the two isolated populations may begin to differ genetically.
Interbreeding would not occur if the two populations were brought back together because they would become so different.
Speciation is said to have taken place at that point.
Speciation may be caused by anything that fragments a population.
The diagrams of allopatric and sympatric speciation can be found in the following.
Speciation may occur when two populations are separated.
Allopatric speciation can be caused by mountain ranges, canyons, rivers, lakes, glaciers, altitude, or longitude.
In certain circumstances, speciation may occur without geographic isolation, in which case the cause of the speciation is sympatric.
Polyploidy, habitat isolation, behavioral isolation, temporal isolation, and reproductive isolation are examples of sympatric speciation.
Polyploidy is when a cell has more than two complete sets of chromosomes.
It can happen naturally or through breeding.
A daughter cell with 4 n chromosomes is formed when gametes with the 2 n chromosomes are fertilized by another abnormal 2 n gamete.
Plants that are polyploid cannot breed with other plants that are not polyploid and are functionally isolated from them.
Habitat isolation is when two organisms live in the same area.
There are two species of snake that can be found in the same area, one of which is in the water.
Sticklebacks, small saltwater fish that have been studied extensively, have elaborate mating behavior.
In response to increased sunlight, the males change in color and form a red belly.
The male builds a nest and courts the female with a dance that causes a complex set of movements between the partners.
No young are produced if either partner fails in any part of the dance.
Male fireflies signal to females of their kind by blinking the lights on their tails.
Females only respond to their own species of males.
If the female doesn't respond with the correct blinking pattern, there won't be sex.
The two animals are not in contact with each other.