definition of evolution a process by which modern organisms have descended from ancient organisms...
TRANSCRIPT
Definition of Evolution
• A process by which modern organisms have descended from ancient organisms
and/or
• Any change in the frequency of an allele in a given gene pool
• The voyage of the Beagle
NorthAmerica
Great Britain Europe
Africa
Equator
Australia
Tasmania
NewZealand
Cape ofGood Hope
SouthAmerica
An
des
Cape Horn
Tierra del Fuego
GalápagosIslands
PacificOcean
AtlanticOcean
Darwin’s Contemporaries
• Lamark
• Weismann
• Lyell
• Wallace
• Malthus
• Fossils and the fossil record strongly support the theory of evolution
– Hominid skull
The study of fossils provides strong evidence for evolution
– Petrified trees
– Ammonite casts
– Fossilized organic matter in a leaf
– Scorpion in amber
– “Ice Man”
• The fossil record shows that organisms have appeared in a historical sequence
• Many fossils link early extinct species with species living today
– These fossilized hind leg bones link living whales with their land-dwelling ancestors
• Other evidence for evolution comes from
– Biogeography
– Comparative anatomy
– Comparative embryology
Evidence to validate the evolutionary view of life
Human Cat Whale Bat
– Molecular biology
Human Rhesus monkey Mouse Chicken Frog Lamprey
Last commonancestor lived26 million yearsago (MYA),based onfossil evidence
80 MYA
275 MYA
330 MYA
450 MYA
• Darwin observed that
– organisms produce more offspring than the environment can support
– organisms vary in many characteristics
– these variations can be inherited
• Darwin saw natural selection as the basic mechanism of evolution
– Human involvement-Breeding
Darwin proposed natural selection as the mechanism of evolution
– Example of artificial selection in animals: dog breeding
German shepherd Yorkshire terrierEnglish springer
spanielMini-dachshund Golden retriever
Hundreds tothousands of years
of breeding(artificial selection)
Ancestral dog
• These five canine species evolved from a common ancestor through natural selection
Figure 13.4C
African wilddog
Coyote Fox Wolf Jackal
Thousands tomillions of years
of natural selection
Ancestral canine
• The evolution of insecticide resistance is an example of natural selection in action
Chromosome with geneconferring resistanceto insecticide
Additionalapplications of thesame insecticide willbe less effective, andthe frequency ofresistant insects inthe populationwill grow
Survivor
Insecticideapplication
• A gene pool is the total collection of genes in a population at any one time
• Microevolution is a change in the relative frequencies of alleles in a gene pool
Microevolution is change in a population’s gene pool over time
• Hardy-Weinberg equilibrium states that the shuffling of genes during sexual reproduction does not alter the proportions of different alleles in a gene pool
– To test this: The imaginary, nonevolving population of blue-footed boobies
The gene pool of a nonevolving population remains constant over the generations
Webbing No webbing
• We can follow alleles in a population to observe if Hardy-Weinberg equilibrium exists
Phenotypes
Genotypes
Number of animals(total = 500)
WW
320
Ww
160
ww
20
Genotype frequencies 320/500 = 0.64 160/500 = 0.32 20/500 = 0.04
640 W 160 W + 160 w 40 w
800/1,000 = 0.8 W 200/1,000 = 0.2 w
Number of allelesin gene pool(total = 1,000)
Allele frequencies
Recombinationof alleles fromparent generation
Next generation:
Genotype frequencies
Allele frequencies
SPERM EGGS
0.64 WW 0.32 Ww 0.04 ww
0.8 W 0.2 w
WWp2 = 0.64
WWqp = 0.16
Wwpq = 0.16
wwq2 = 0.04
W sperm
p = 0.8
w sperm
q = 0.2
W e
gg
p = 0
.8
w egg
q = 0
.2
• Public health scientists use the Hardy-Weinberg equation to estimate frequencies of disease-causing alleles in the human population
– Example: phenylketonuria (PKU)
Connection: The Hardy-Weinberg equation is useful in public health science
• The population is very large
• The population is isolated
• Mutations do not alter the gene pool
• Mating is random
• All individuals are equal in reproductive success
Five conditions are required for Hardy-Weinberg equilibrium
• Genetic drift is a change in a gene pool due to chance
– i.e., the change in allele frequencies over time
– Genetic drift can cause the bottleneck effect and vice versa
13.11 There are several potential causes of microevolution
Originalpopulation
Bottleneckingevent
Survivingpopulation
– or the founder effect
• Gene flow can change a gene pool due to the movement of genes into or out of a population• Mutation changes alleles
• Natural selection leads to differential reproductive success
Genetic Drift and/or Founder Effect Can Lead to Another example of Evolution: Adaptive Radiation
• Adaptive radiation describes the rapid speciation of a single or a few species to fill many ecological niches. This is an evolutionary process driven by mutation and natural selection.
• Three Types:
– General adaptation. A species that develops a radical new ability can reach new parts of its environment. An example of general adaptation is bird flight.
– Environmental change. A species that can, in contrast to the other species in the ecosystem, successfully survive in a radically changed environment will probably branch into new species that cover the new ecological niches created by the environmental change. An example of adaptive radiation as the result of an environmental change is the rapid spread and development of mammalian species after the extinction of the dinosaurs.
– Geographic isolation. Isolated ecosystems, such as archipelagos and mountain areas, can be colonized by a species which upon establishing itself undergoes rapid divergent evolution. Darwin's finches are examples of adaptive radiation occurring in an archipelago.
• Natural selection results in the accumulation of traits that adapt a population to its environment
– If the environment should change, natural selection would favor traits adapted to the new conditions
Adaptive change results when natural selection upsets genetic equilibrium
• Many populations exhibit polymorphism and geographic variation
• Some variations may be neutral, providing no apparent advantage or disadvantage…or does it?
– Example: human fingerprints
Not all genetic variation may be subject to natural selection
• Low genetic variability may reduce the capacity of endangered species to survive as humans continue to alter the environment
– Studies have shown that cheetah populations exhibit extreme genetic uniformity
– Thus they may have a reduced capacity to adapt to environmental challenges
Connection: Endangered species often have reduced variation
• An individual’s Darwinian fitness is the contribution it makes to the gene pool of the next generation relative to the contribution made by other individuals
• Production of fertile offspring is the only score that counts in natural selection
The perpetuation of genes defines evolutionary fitness
13.19 There are three general outcomes of natural selection
Fre
qu
en
cy
of
ind
ivid
ua
ls
Originalpopulation
Phenotypes (fur color)
Originalpopulation
Evolvedpopulation
Stabilizing selection Directional selection Diversifying selection
• Sexual selection leads to the evolution of secondary sexual characteristics
– These may give individuals an advantage in mating
Sexual selection may produce sexual dimorphism
• Why?
– historical constraints
– adaptive compromises
– chance events
– availability of variations
Perfection is impossible…