How Populations Evolve Text Reading: Ch 10 & 11 Learning Objectives • Explain the two major points of Charles Darwin’s theory of evolution. • Describe how natural selection is more a process of editing than a process of creation. • Explain how biological classification, the fossil record, biogeography, comparative anatomy, comparative embryology, vestigial structures, and DNA similarities provide evidence of common descent. • Discuss the evidence that humans and great apes share a recent common ancestor.
Transcript
How Populations EvolveText Reading: Ch 10 & 11
Learning Objectives
• Explain the two major points of Charles Darwin’s theory of evolution.
• Describe how natural selection is more a process of editing than a process of creation.
• Explain how biological classification, the fossil record, biogeography, comparative anatomy, comparative embryology, vestigial structures, and DNA similarities provide evidence of common descent.
• Discuss the evidence that humans and great apes share a recent common ancestor.
What is Evolution?Evolution: Change in the ____________________
___________________of organisms that occurs over the course of generations.
• Evolutionary changes are inherited via genes.
• Other changes may take place because of environmental changes and are not necessarily evolutionary.
• 1960s, the WHO began a campaign to eradicate the mosquitoes that transmit malaria.
• Used DDT, to which some mosquitoes have evolved resistance.
Persistent Pests: DDT-resistant mosquitoes
The Process of Evolution• Populations evolve, NOT individuals.
• The genetic makeup of a population ____________ _________________________________________.
• Mosquitoes and DDT example:
• Individuals without a gene for resistance died
• Over time, the population changed to mostly resistant individuals
• Initially, the frequency of the DDT-resistant allele was low. Over time, it became more frequent.
Natural selection: in a population, individuals with certain heritable traits can _______________ ___________better than other individuals without these traits.
– Individuals with these traits leave _______ offspring than others.
– The offspring tend to have these traits that are favorable for that environment.
– Thus, over time the frequency of the favorable traits _____________ in the population.
Natural Selection
Evolution by Natural Selection
• Examples of natural selection include
– Pesticide resistance in crop-eating insects.
– Antibiotic resistance in infectious bacteria
– Drug-resistant strains of HIV
• The result of natural selection is evolutionary adaptation.
Adaptation: an inherited characteristic that _______________ an organism’s ability to survive and reproduce in a particular environment.
Evolutionary Adaptation
• The result of natural selection is evolutionary adaptation.
Evolutionary Adaptation
The Peppered Moth
Microevolution vs Macroevolution
• Microevolution: changes that occur within a species and the characteristics of a population. Easily observed, relatively non-controversial.
• Macroevolution: changes that occur, as a result of microevolution, over long periods of time and result in the origin of new species. Controversial among non-biologists.
The Theory of Common Descent
• All species present on earth today are descendents of a single common ancestor.
• All species represent the product of millions of years of accumulated evolutionary changes.
Organisms observed today
EvolutionEvolution
Common ancestor
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Early Views of Evolution
• Charles Darwin is considered to be the father of modern evolution. However, he did not “invent” the idea.
• Early philosophers debated whether species were fixed or changed over time.
– Aristotle (384-322 B.C.): species fixed, do not evolve
– Judeo-Christian culture: fortified idea, Earth ~6,000 yrs old
– Anaximander (611-546 B.C.): humans evolved from fish that had moved onto land
Early Views of Evolution (cont’d)
• Jean Baptiste Lamarck (1809): Inheritance of Acquired Characteristics
– Organisms evolve by the process of adaptation
– All organisms had an innate, inner drive for perfectionism that led them to develop new characteristics
– Acquired characteristics could be passed on to offspring
Charles Darwin
• Father of modern evolution (Darwinism)
• Ideas shaped by
– Voyage of the HMS Beagle
• Employed as ship’s naturalist
• Collected thousands of specimens
• Observed various adaptations in organisms
– Principles of Geology by Charles Lyell.
• Postulated Earth was old and changes occurred over long periods of time
Darwin and the Voyage of the Beagle
• December 1831, Darwin left Great Britain on the HMS Beagle
• Darwin intrigued by
– Geographic distribution of organisms on the Galápagos Islands.
– Galápagos organisms resembled those in South America.
The Voyage of the Beagle (cont’d)
~600 mi
Galapagos Islands tortoises vary with their environments. Each island had tortoises, but each island had a different type.
He noted a similar pattern with iguanas. Each island had its own type, yet they had similarity to each other and to the ones on the mainland.
Darwin and The Origin of Species
• 1859, Published On the Origin of Species by Means of Natural Selection
1. Contemporary species were not created in their present form but evolved from ancestral species by modification over time (ie decent with modification).
2. Proposed a mechanism for evolution: NATURAL SELECTION
• 1836, Returned to Great Britain but did not publish his ideas immediately.
Darwin’s Theory of Natural Selection
• Based his theory of natural selection on 2 key observations:
• Observation 1: Overproduction
– All species tend to produce excessive numbers.
– This leads to a struggle for existence.
• Observation 2: Individual variation
– Variation exists among individuals in a population.
– Much of this variation is heritable.
Hypotheses on the Origin of Modern Organisms
Difference in form
Difference in form
Difference in form
Difference in form
(b) TransformationSpecies arise separately but do change over time inorder to adapt to the changing environment.
(d) Common descentSpecies do change over time, and newspecies can arise. All species derivefrom a common ancestor.
(a) Static modelSpecies arise separatelyand do not change over time.
(c) Separate typesSpecies do change over time, and new species can arise; but each group of species derives from a separate ancestor that arose independently.
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Evidence of Evolution
• Several lines of biological evidence point to a common ancestor:
– Biological classification
– Anatomical similarities between organism
– Shared developmental pathways
– Useless traits in modern species
– DNA and protein similarities
– Distribution of organisms on Earth (biogeography)
– Fossil evidence
Biological Classification
• Organisms classified into a hierarchy according to biological similarities
• Linnean classification:
Most inclusive groups (share general characteristics)
Least inclusive groups (share many detailed characteristics)
Bat Sea lion Lion Chimpanzee Human
Humerus
Radiusand ulna
Carpals
Metacarpals
Phalanges
Anatomical Similarities between Organisms
• Comparative anatomy: comparison of body structure ___________________________________________.
• Homology: similarity in structures due to common ancestry.
• Example: Mammalian forelimbs have the same set of bones. The underlying structure is similar despite the very different functions.
Snake Chicken Possum Cat Bat Human
PharyngealslitsEarly
embryo
Intermediateembryo
Lateembryo
Tail
Shared Developmental Pathways• Comparative embryology: comparison of structures that
appear during _______________________________ ___________________________________________.
• Example: comparative embryology of vertebrates
Useless Traits in Modern Species
• Vestigial structures: rudimentary structures that do not have a function in modern species but were functioning in ancestral species.
• Examples:
Boa-constrictors grow tiny hind legs
Duckbill platypuses grow and re-absorb teeth before birth
Human coccyx and prenatal tail
Human appendix
Human wisdom teeth
DNA and Protein Similarities
• Evolutionary relationships can be determined by comparing ________________________________ of different organisms.
• More closely related species have more similarity in DNA and protein sequences than more distantly related species.
Biogeography
• Biogeography: the study of the _____________ _______________________________ of species.
• Related species should be close to each other.• Example: Different species of mockingbird found
on Galapagos Islands all resemble another species found on the mainland.
Biogeography
• Continents were once all united
The Fossil Record
• Fossils: preserved remnants or impressions left by organisms that lived in the past.
– Are often found in sedimentary rocks.
• Fossil record: ordered sequence of fossils as they appear in rock layers.
• Reveals the appearance of organisms in a historical sequence.
• Contains transitional forms that link past and present.
Fossil Evidence
Hyracotherium(Eohippus)
Mesohippus
Merychippus
Equus
4 toes
3 toes
3 toes
1 toe
Horse ancestor Modern horse
55 40 17 4
Millions of years ago
Humans and Apes Share a Common Ancestor
• The same lines of evidence that support common descent can be used to look for the closest relatives of humans.
• Are humans related to apes?
Biological Classification of Humans
Kingdom(Animalia)
Phylum(Chordata)
Domain(Eukarya)
Class(Mammalia)
Order(Primates)
Family(Hominidae)
Genus(Homo)
Species(Homo sapiens)
Linnaean classification
Biological Classification of Humans
Mammal ancestor
Squirrelmonkey Orangutan Gorilla
Commonchimpanzee Bonobo Human
increase in size ofgenital structures
delayed sexual maturitybroad incisors
shortened canine teethenlarged brow ridges
elongated skullreduced hairiness
large brain
increased flexibility of thumbmore erect posture
no tail
Order Primates
Family Hominidae
Subfamily Homininae
Shared characteristics of humans and apes
DNA Similarities
• The DNA sequences of humans and great apes are highly similar
