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Evolution: A history and a process
Charles Darwin= Father of the Theory of Evolution• Evolution= all of the changes that have
transformed life over an immense time
• Two ideas persisted before Darwin– Species are fixed– Earth was less than 10,000 years old and
also unchanging
Before Darwin…
• 1800s Jean Baptiste Lamarck– Proposed that life evolves and that species
are not permanent– Process of adaptation
Other scientists• Charles Lyell- geologist
– Proposed the gradual and observable geologic processes
• Erosion, formation of mountains
– Darwin confirmed this when he witnessed an earthquake in Chile that moved a portion of land above sea level
• Thomas Malthus– Proposed that a population’s growth is
influenced by resources
• Darwin left England as a young graduate• He returned as a famous naturalist• 1844 Darwin wrote a 200 paper essay that
described his idea…but was not published• 1858 Alfred Wallace came to the same
conclusions as Darwin• Within a month, some of Wallace’s, as well
as Darwin’s ideas, were presented to the public jointly
• One year later, Darwin published his book The Origin of Species
• Darwin made two points in his book:1. Species on Earth today descended from
ancestral species• These descendants spread into different
habitats around the world and acquired adaptations for a diversity of life
• “Descent with modification”• Ex: jackrabbit and showshoe hare
2. Natural selection is the mechanism for evolution• Natural selection is the process by which
individuals with inherited characteristics that are ideal to the environment leave more offspring on average than do other individuals
Evolution leaves signs
• Evolution leaves evidence in – The fossil record– The diverse assortment of modern species
• Fossil record– Fossils= preserved remains or markings left by
organisms that lived in the past • Found mostly in sedimentary rocks• Sedimentation causes rock formation as particles
accumulate in layers; any given stratum (layer) is older than the one above it, and younger than those below
• Paleontologist= scientist who studies fossils
• Oldest fossil evidence of life consists of chemical traces in rocks that are 3.8 billion years old– Found in Greenland
• Prokaryote fossils have been found and dated as 3.5 billion years old
• Fossil example:– Basilosaurus= an early whale found to
have remnants of hind leg bones
• Geographic Distribution• Darwin observed the similarities and
differences of organisms from different parts of the world– Darwin proposed that organisms present today
evolved from ancestral forms
• Geographic distribution can be used as a clue for the evolution of species
• Biogeography is the study of the distribution of plants and animals throughout the world
• The world’s six biogeographical regions have their own distinct mix of living things
• Continental drift refers to the changing positions of the continents over time
• Two hundred twenty-five million years ago, all the present land masses belonged to one continent (Pangaea)
• The distribution of plants and animals is consistent with continental drift
• Organisms, such as certain seed plant groups or reptiles, are widely distributed throughout the world
• Other groups, such as mammals that arose after the continents broke up, have great differences in species on different continents
• Clues to evolutionary history– Similarities in Structure– Example: mammal forelimb – Homologous structures= similar
structures in species haring a common ancestor
• “Descent with modification”
• Proposed by Darwin
• Modification of structures to take on new functions
• Vestigial structures= remnants of structures that may have served an important function in an ancestral species, but have no clear function in some of the modern descendents– Often smaller in size
• Ballene whale
• Developmental similarities• Embryos of closely related species have similar
stages of development
• Bones of the skeleton form in a common pattern• The process of comparing how certain structures
develop in different organisms is comparative embryology.
• Molecular biology– Comparison of DNA sequences
between species
– If the two species’ sequences match closely then it is thought that the two species are related to a common ancestor
– If the two species’ sequences have many differences they probably do not share common ancestry
Comparison of Hemoglobin
• Artificial selection= selective breeding of domesticated plants and animals to produce offspring with genetic traits that humans value
• Munchkin cats
Artificial Selection
Collie Sheltie
• In contrast, natural selection favors traits that are beneficial to the organisms in their environment
• The environment does the “selective breeding”
• Resulting in evolutionary adaptation
Natural Selection of Flies
• Darwin could not explain how variations passed from one individual to the next
• Gregor Mendel to the rescue!!– Microevolution…a change in a population’s gene
pool– Gene pool= consists of all the alleles in all the
individuals that make up a population• Where genetic variation is stored• Example: Wild mustangs
– What leads to genetic variation?• Mutations • Sexual recombination
• Natural selection is not random• Why?
– The environment favors combinations of genes that contribute to survival and reproductive success
– Some alleles may become more common in a gene pool than others
• Frequency of alleles= how often certain alleles occur in the gene pool
– Usually expressed as a percentage
• Microevolution– Blending of Mendel’s and Darwin’s theories to
look at evolution based on genetics– Generation to generation changes (smallest scale)
Microevolution
• What causes gene pools to change (besides natural selection)?
1. Genetic drift= a change in the gene pool of a population due to chance • All populations are subject to genetic drift• Bottleneck effect…a drastic reduction in the
size of a population– Usually by natural disaster…and only a few
remaining individuals are left to start a new population• Ex: cheetah population in Africa
• Founder effect…genetic drift in a new colony– When a few individuals leave the original
population and start a new population
Genetic Drift
• 2. Gene flow= movement of alleles between populations– Occurs when fertile individuals mate with
individuals from other populations– Ex: a wind storm might blow pollen from a
population of only red flowers to a population consisting of only white flowers
– Reduces the genetic differences between populations
– Can eventually mix the two populations
So how did humans evolve?
• A very lengthy process in which people originated from apelike ancestors.
• The evolution of humans has occurred over the last 6 million years.
• Bipedalism – walking on 2 legs – 4 million years ago
• Most advanced traits have occurred over the last 100 million years.
• Apes have a very large, very strong lower jaw to support their carnivorous eating.
• As the shape of the human skull evolved to have a smaller lower jaw, this allowed for a larger brain to develop.
• With a larger brain, the capacity for language and the manufacture of tools were able to be developed.
• Fitness = the contribution that an individual makes to the gene pool of the next generation compared to the contributions of other individuals
So what does “survival of the fittest” mean?
How does 1 species become 2 species?
Species = a population or group of populations whose members can interbreed and produce fertile offspring– Speciation = the formation of a new species
Reproductive isolation = when populations become reproductively isolated, they can evolve into two separate species
• Interbreeding links members of a species genetically
• If the members stop interbreeding, then the gene pool can split
3 ways Reproductive Isolation can develop
1. Behavioral isolation = when two populations develop differences in courtship rituals or other behaviors that prevent them from interbreeding
• Eastern and Western Meadowlarks don’t respond to eachothers songs
3 ways the reproductive isolation can develop
2. Geographic isolation = when two populations are separated by geographical barriers (rivers, mountains, bodies of water)
• Grand Canyon isolated a small population of Albert’s squirrel on the northern rim
• Separate gene pools formed, natural selection and genetic drift worked separately on each group which led to the formation of a distinct subspecies called the Kaibab Squirrel
3 ways the reproductive isolation can develop
3. Temporal isolation = when two or more species reproduce at different times of the day, season, or year
• There are 13 billion known species of organisms
• This is only 5% of all organisms that ever lived!!!!!
• New organisms are still being found and identified
Species of Organisms
What is Classification?
• Classification = is the arrangement of organisms into orderly groups based on their similarities
• Classification is also known as taxonomy– Benefits:
• Accurately and uniformly names organisms• Prevents misnomers
– Ex: jellyfish, seahorse
Confusion in Using Different Languages for Names
Latin Names are Understood by all Taxonomists
Carolus Linnaeus1707 – 1778
• 18th century taxonomist – “Father of Taxonomy”
• Classified organisms by their structure
• Developed naming system still used today
Standardized Naming• Two-word name
(Genus & species) = Binomial Nomenclature
• Latin or Greek• Genus is
capitalized, species is not
• Italicized in print• Underlined if
handwritten
American Robin
Turdus migratorius
Binomial Nomenclature
Which TWO are more closely related?
Rules for Naming Organisms
• The International Code for Binomial Nomenclature contains the rules for naming organisms
• All names must be approved by International Naming Congresses (International Zoological Congress)
• This prevents duplicated names
Classification Groups• Taxon ( taxa-plural) is a category
into which related organisms are placed
• There is a hierarchy of groups (taxa) from broadest to most specific
• Domain, Kingdom, Phylum, Class, Order, Family, Genus, species
•
• Domain• Kingdom• Phylum• Class• Order• Family
• Genus• Species
BROADEST TAXON
MOST
SPECIFIC
Hierarchy – Taxonomic Groups
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• Dumb• King
• Phillip
• Came
• Over
• For
• Gooseberry
• Soup!
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• Broadest, most inclusive taxon
• Three domains
• Archaea and Eubacteria are unicellular prokaryotes (no nucleus or membrane-bound organelles)
• Eukarya are more complex and have a nucleus and membrane-bound organelles
Domains
Cladogram• Diagram showing how organisms are related
based on shared, derived characteristics such as feathers, hair, or scales
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Primate Primate CladograCladogra
mm
Dichotomous Keying
• Used to identify organisms
• Characteristics given in pairs
• Read both characteristics and either go to another set of characteristics OR identify the organism
Dichotomous Key
•1a Tentacles present – Go to 2•1b Tentacles absent – Go to 3•2a Eight Tentacles – Octopus•2b More than 8 tentacles – 3•3a Tentacles hang down – go to 4•3b Tentacles upright–Sea Anemone•4a Balloon-shaped body–Jellyfish•4b Body NOT balloon-shaped - 5
