Chapter 15 Sec 1 & 2Evolution

Darwin And the Galapagos

• Charles Darwin set sailed on a boat called the Beagle.– The main purpose of the voyage was to survey the coast of

South America– It took five years and within the five years, Darwin collected

fossils, rocks, plants and animals.• In 1835, the Beagle arrived at the Galapagos islands off

the coast of South America. – Darwin was first unimpressed by the Islands because of how

barren the volcanic islands were. – But after collecting several mockingbirds, Finches and other

animals, he was surprised at the diversity of animals.

Darwin And his specimens• When he returned to England, he brought his

specimens back to another scientist. – Even though the Finches and Mockingbirds he

brought back were similar to the ones in South America

– But almost all the specimens were new species. – These species of animals was not found anywhere

in the world, only in the Galapagos. – The scientist was surprised, because species from

South America shouldn’t have changed at all.– Darwin suspected that these things happened by

the animals adapting to their new environment.

Darwin’s Theory

• Darwin hypothesized that new species could appear gradually through small changes in ancestral species. – He experimented by observing pigeon breeders that

would breed them by artificial selection. • Breeding that would produce offspring's with desired traits.• Ex. If a human wanted a bird with a spiral tail, then they

would breed a bird with a spiral tail.– Darwin thought, if this can happen by human then

nature could do this as well to adapt to a new environment over a period of time.• Like his specimens

Darwin's Theory

• Darwin read a column from an ecologist stating that, the human population will become so overpopulated that it will compete for food.– He thought that this most happen within nature

with species. – He thought that the most well adapted species will

be able to exist better then species that weren’t• The less equipped would die

– This was known as Natural Selection.

4 principles of Natural Selection• This theory had 4 principles:• 1) There had to be variations within populations

over time. • 2) These variations can be inherited– Passed from generation to generations.

• 3) Organisms have more offspring than can survive on available resources.

• 4)Organisms with variation can reproduce more offspring that can survive better than other organisms offspring.

The origin of Species• From Natural Selection he hypothesized that if

organisms showed variations within the same species, that they could of originated from a common ancestor. – In other words, Natural selection could be the mechanisms

for the origin of species. • After reading an article from another scientist that

proposed the same theory, Darwin published his book “the origin of species”.– This is the book that explain natural selection as the

mechanism of the origin of species– Darwin used the term Evolution only once in the book, and it

was on the last page of the book. • Evolution is cumulative changes in groups of organisms through

time.

Evidence to support Natural Selection

• Comparative embryology- shows adaptive or evolutionary relationships within vertebrate embryos.

• Scientist found homologous structures within vertebrate embryos that aren’t their when they become an adult.– Ex. A structure that is called pharyngeal pouches

that develop into gills, within fish, and ears, jaws and throats within mammals.

– Ex. All vertebrates embryos have tails. Including us.

Geographic distribution • Darwin notice this on the Galapagos islands– He notice a mar (rabbit like creature) was the same as a

rabbit in England. • Only differences was color and some features.

– He saw a mocking bird that was grey in color. – But he then saw that the mar and mocking bird shared

more similar traits with South America then the species in England

– This is because the islands was closer to South America– Making migrations of species and plants to come to the

islands.• After generations of organisms started to develop diversity within

speciesThis is called Geographic distribution

Geographic distribution

• This have been proven by today’s field called Biogenesis. – Adaptation is connected by climate and geological

forces that explain many ancestral relationships and geographic distributions seen in fossils and living organisms.

Adaptation

• An Adaptation is a trait shaped by natural selection that increases an organism’s fitness.

• Fitness- it is the percentage that an organism off spring will survive.

• An organisms ability to adapt heightens its percentage of fitness

• Here are a few examples of adaptations – Mimicry, camouflage, antimicrobial resistance

Adaptation

• Mimicry- is a morphological adaptation that one species evolves to resemble another species.

Adaptation

• Camouflage- is a morphological adaptation of organisms that allow them to blend into there surroundings.

Mechanisms for Evolution• Natural Selection remains a central theme in

Evolution, but it is not the only theorized mechanism for it. – Another is from studies of population genetics and

molecular biology. • One is the Hardy-Weinberg princple.– States when allelic frequencies remain constant,

population is in genetic equilibrium. • These are two scientist that came up with this theory.• A mathematician, Godfrey Hardy and Germany physician

Wilhelm Weinberg.

Population Genetics• Five conditions for genetic equilibrium:• 1) No genetic drift– Genetic drift is Any change in the allelic frequencies in a

population that results from chance. • 2) No gene flow– Gene Flow is when new genes from one population is

introduced to a new population. • 3)No mutations• 4) mating must be random• 5)no natural selection! • In other words everything must stay the same.

Population Genetics

• Populations in nature might meet some of these requirements.– But never all 5 for a long period of time.

• If a population is not in genetic equilibrium then 1 of the 5 conditions have been violated.– When this happens, evolutionary changes occurs. – This is one evidence to support a mechanism for

evolution.

Genetic Drift

• Any change in the allelic frequencies in a population that results from chance is Genetic Drift

• In large populations, there are enough alleles to drift to ensure that the population will remain constant from one generation to the next.

• In smaller populations, the chance of losing an allele becomes greater.

• Ex: Founder effect and bottleneck.

Founder Effect

• An extreme example of genetic drift if the founder effect.– The Founder effect- when a small population

separates from a larger population and interbreeds, producing unique characteristics.

– This is seen within Amish and Mennonite communities.

– The result is a syndrome called 6-finger dwarfism.

Bottleneck• Another example of extreme genetic drift is

Bottleneck– Bottleneck- is when a large population declines to a low

number and then rebounds greatly.• When the population rebounds, the population is

genetically similar of what it was at the lowest number. – This reduces genetic variation. – It is important to note that when there is low genetic

variation, inbreeding can happen– This decreases fertility and can add to extinction.

Coevolution • Many species could of evolve in close relationship

with other species. • If this happens, The relationship might be so close

that the evolution of one species affects the evolution of other species.– This is called Coevolution. – Mutalism is a form of coevoltuion.• Mutalism is when two species benfit each other.

– Example of coevolution and mutualism is pollinated plants and their pollinators.• Ex. Comet orchids and the moths that pollinated them benefit

each other.– The flower is foot-long perfectly match the foot-long tongue of the

moth.

Convergent evolution

• Sometimes unrelated species evolve similar traits even though they live in different parts of the world. – This is convergent evolution.

• This happens in environments that are geographically far apart but have the same ecology and climate.

Rates• Most scientist think that evolution proceeds in small,

gradual steps. – This is called Gradualism. – A great deal of evidence supports this theory.– The fossil records do contains instances of abrupt transitions.• Ex. Snails in the fossil records look the same for millions of years, and

then the shell shape changed dramatically in only a few thousand years.

• The theory of punctuated equilibrium attempts to explain such abrupt transitions in the fossil record. – According to this theory, rapid spurts of genetic change cause

species to diverge quickly.

Rates

• These periods punctuate much longer periods when the species exhibit little change.

• The tempo for these theories in evolution leaves questions in the theory of evolution.– Do most evolution occur gradually or in short

bursts?– If it shows short burst, then a species can diverge

from a common ancestor by a couple thousands of years instead of millions.