Download Evolution

 Evolution:
 Process by which modern organisms have descended
from ancient organisms
 Change over time
 Theory:
 A well supported explanation of phenomena that have
occurred in the natural world
 Father of Evolution
 Born in England in 1809
 After college, in 1831, he joined the crew of the H.M.S.
Beagle and sailed around the world for 5 years.
 This was one of the most important voyages in the
history of science.
 During his travels, Darwin made numerous
observations and collected evidence that led him to
propose a revolutionary hypothesis about the way life
changes over time.
 During his travels, Darwin saw great diversity.
 In a single day, he found 68 species of beetles and he
wasn’t even looking for them!
 Darwin saw that only certain animals lived in certain
places even when the climates were the same.
 While on his journey, Darwin collected many fossils
(preserved remains of ancient organisms)
 Some fossils resembled present-day organisms, while
others looked completely different.
 Located 600 miles off the west coast of Ecuador
 13 large islands, 6 small islands, and many other islets
and rocks
 The islands all vary in climate and life
 Similar temperatures
 Varying amounts of rain (depends on height of island)
 Some islands were covered in plant and animal life, others
had very few organisms
 Depends on rain and volcanic activity
 Darwin looked at tortoises and noticed that the tortoises
on different islands had different characteristics.
 He also looked at finches and collected many specimens
and noticed that each had a different shaped beak
 The different shaped beaks came from different islands
 He concluded that the beak shape was a result of the available
food sources on each island.
Isabela Island
Pinta Island
Hood Island
How are each of the tortoises different?
 By the time Darwin went on his voyage, many
discoveries had turned up important pieces of
evidence.
 The most important = The Fossil Record – made
scientists question their beliefs and forced them to
adjust their ideas
 During the 18th and 19th centuries, Earth was being
studied in great detail
 Scientists gathered information suggesting that the
Earth was very old and had changed slowly over time.
 James Hutton
 Proposed that layers of rocks form very slowly
 Some rocks are moved up by forces beneath the Earth’s
surface, others are buried, and others are pushed up
from the sea floor to form mountain ranges.
 Because of these things, Hutton proposed that the Earth
had to be much older than a few thousand years
 Charles Lyell
 Stated that one must explain past events in terms of
processes that they can actually observe, since processes
that shaped the Earth millions of years earlier continue
in the present
 He recognized that living things change over time and
that all species were descended from other species.
 Also realized that organisms were somehow adapted to
their environments.
 Proposed 3 hypotheses:
1.
Tendency Towards Perfection – organisms are
continually changing and acquiring features that help
them live more successfully in their environments
ex. Birds acquired the urge to fly – birds kept trying to fly
and over time they grew wings
2.
Use and Disuse – organisms could alter the size or
shape of particular organs by using their bodies in new
ways
ex. By trying to use their front limbs for flying, birds could
eventually transform those limbs into wings
ex. If a winged animal did not use its wings, the wings
would decrease is size over generations and finally
disappear
3.
Inheritance of Acquired Traits – inheritance of a trait
that your parents acquired sometime in their life
ex. If your father lifts weights and has large muscles, you
would inherit large muscles.
 Lamarck’s ideas are incorrect in several ways:
 He didn’t know how traits were inherited.
 He did not know that an organism’s behavior has no
effect on its heritable characteristics.
 Though incorrect, Lamarck was one of the first to
realize that organisms are adapted to the
environments.
 In 1858, Alfred Wallace wrote Darwin an essay that
summarized his own thoughts on evolution and
natural selection.
 This gave Darwin the courage to present his own work.
 In 1859, On the Origin of Species was published.
 Darwin’s book described two things:
 Mechanism for evolution = natural selection
 Also explained the evidence behind his ideas
 Darwin knew that traits were passed from parent to
offspring
 Heritable variation – differences that are passed from
parent to offspring
 Even though Darwin didn’t know how heredity
worked, he argued that variation did matter.
 He argued that humans used these variations to their
advantage when it came to farming.
 Those cows that produced the most milk were used for
mating; the cows that didn’t produce much milk were
ignored.
 Artificial Selection – nature provides the variation, and
humans select those variations they find useful
 Struggle for Existence –
 Members of the same species compete regularly to
obtain food, living space, and other necessities of life
 Darwin used Thomas Malthus’ idea to help him.
 Malthus reasoned that if the human population continued to
grow unchecked, sooner or later there would be insufficient
resources for everyone.
 Darwin applied this to all living things.
 In this struggle, the predators that are faster or have a
particular way of hunting will catch more prey. Those
prey that are faster, better camouflaged, or better
protected can better avoid being caught.
 Survival of the Fittest
 Fitness – the ability of an individual to survive and
reproduce in its specific environment
 Central to Darwin’s idea of natural selection
 Adaptation – any inherited characteristic that increases
an organism’s chance for survival
 Successful adaptations enable organisms to become better
suited to their environment and thus better able to survive
and reproduce.
 Survival of the Fittest (continued)
 Survival of the fittest (aka natural selection) –
individuals that are better suited to their environment
survive and reproduce more successfully
 Nature selects for those that are best fit
 Only certain individuals of a population reproduce
 Over time, natural selection results in changes in the
inherited characteristics of a population. These changes
increase a species fitness in its environment.
 Survival of the Fittest (continued)
 Example – Bernard Kettlewell and the Peppered Moths
 Kettlewell studied a population of these moths prior to and
during the Industrial Revolution.
 He studied a population that lived in a wooded area that
contained light gray tree trunks. During this time, a majority
of the moths were gray in color, while only a few were darker
colored.
 As the Industrial Revolution progressed, the trees started to
turn dark gray or black due to all of the pollution.
 The moths then evolved – Nature selected for those moths
that blended in – the population eventually became mostly
dark gray or black with very few lighter colored moths.
 Descent with Modification
 Darwin proposed that over long periods, natural
selection produces organisms that have different
structures, establish different niches, or occupy different
habitats.
 This results in species looking different from ancestors.
 Each living species has descended, with slight changes,
from other species over time
 Common descent – all species (living and extinct) were
derived from a common ancestor
 This is shown by the “Tree of Life”
 Fossil Record
 Darwin saw fossils as a record of the history of life
 Compared fossils from newer rock layers to older rock
layers to see how life has changed over time
 Geographic Distribution of Species
 Different species of animals that are found in similar
environments will evolve to have similar features
 Homologous Structures
 These are structures that have different mature forms
but develop from the same embryonic tissues
 Same structure, different function
 Ex = human hand, whale fin, bird wing
 Analagous Structures
 Structures similar in appears and function but have
different origins and different internal structures
 Different structures, same function
 Ex = Insect wing vs. bird wing
 Ex = whale fin vs. fish fin
 Vestigial Organs
 Structure that serves no useful purpose or function
 Ex = appendix, tailbone
 Embryological Stages
 Embryos are similar at early stages, but become more
different as time goes by
 Individual organisms differ, and some of this variation is
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heritable.
Organisms produce more offspring than can survive, and many
that do survive do not reproduce.
Because more organisms are produced than can survive, they
compete for limited resources.
Each organism has advantages and disadvantages in the struggle
for existence. Individuals best suited to their environment
survive and reproduce most successfully. These organisms pass
their heritable traits to their offspring. Other individuals die or
leave fewer offspring. This process of natural selection causes
species to change over time.
Species alive today are descended with modification from
ancestral species that lived in the distant past. This process, by
which diverse species evolved from common ancestors, unites all
organisms on Earth into a single tree of life.
 Darwin’s theory of evolution by natural selection
explained how life on Earth changed, or evolved, over
many generations.
 What Darwin did not know was how genes, were
passed down through each generation
 In genetic terms, evolution is any change in the relative
frequency of alleles in a population.
 Relative frequency – the number of times an allele
occurs in a population compared to the number of times
other alleles for the same gene occur
 Ex = 20 individuals are TT, 30 are Tt, and 25 are tt
 Frequency of T = 70
 Frequency of t = 80
 There are two main sources of genetic variation
 Mutations – any changes in a sequence of DNA
 Are all mutations bad???
 No!!! If a mutation makes an organism better fit, it is beneficial.
 If a dog is born with a thicker coat in a cold snowy
environment, that mutation would be beneficial.
 However, if that same dog is born with a thick coat in the
desert, that mutation would be bad.
 Gene shuffling – occurs during gamete formation
 It can produce millions of different gene combinations
 Speciation is the formation of new species from existing
species.
 For one species to evolve into a new species, a separation of
populations must occur.
 As new species evolve, populations become reproductively
isolated from one another. This can happen in three ways:
 Behavioral Isolation – occurs when populations have different
courtship and reproductive behaviors.
 Geographic Isolation – occurs when geographic barriers
separate populations
 Temporal Isolation – occurs when populations reproduce at
different times
 There are 3 requirements for speciation to take place:
 Separation of populations
 Changes in the gene pool
 A gene pool consists of all genes found in a population
 Reproductive Isolation