Download 1 Evolution, Variation, and Adaptation

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Evolution, Variation, and Adaptation
-evolution: change over time
-the result of variations within populations over long periods of time
-it can result in:
-different forms of beaks (morphology)
-changes in use (bat wing vs. human hand)
-changes in behavior (feeding, mating, …)
-biologists observed that living organisms were different from the fossil organisms
-they then developed a theory called evolution that organisms change over time
-theory: explains current observations and predicts new observations
-evidence of observations of modern and fossilized organisms from all over the world supports evolution
the theory of evolution
Jean Baptiste Lamarck
-thought living things constantly try to improve their form
-believed in use or disuse
-if an animal uses one parts of its body frequently, that part will become stronger and more
developed
-if an animal doesn’t use a part of its body, that part will slowly weaken, become smaller, and
disappear
-believed these modified structures are inherited by offspring
-however, his theory lacked the ability to predict results
August Weismann
-he tested Lamarck’s idea of inheritance of acquired traits by mating mice whose tails had been bobbed
-when the mice were mated, the offspring had long tails
-this disproved Lamarck’s theory
Charles Lyell and James Hutton
-lyell was a geologist
-promoted a hypothesis first developed by hutton
-he believed that the earth is much older than a few thousand years
-proposed that natural forces that existed in the past were the same as those of today
-he thought natural forces have shaped and continue to shape the surface of the Earth
-this is called uniformitarianism
Charles Darwin
history of Darwin
-had difficulty choosing a career
-was a contemporary of Abraham Lincoln
-was a part of an expedition around South America
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-developed theory of evolution after returning to England
-spent 5 years on HMS Beagle as a naturalist, sketching and collecting plants and animals
-studied finches on the Galapagos Islands and noticed differences in the beaks of birds on different
islands
-wrote an essay of his ideas in early 1840s, but delayed publication because he knew his ideas would be
controversial
what also shaped Darwin’s ideas?
-charles lyell’s idea that the earth has undergone slow, uniform change  Darwin thought that if the
earth is under constant change, this change must affect the viability of plants and animals
-thomas malthus’ idea that the size of a population is limited by the amount of resources and
competition among individuals for them
-malthus said that the number of organisms increases geometrically (very rapid growth) and the
food supply increases arithmetically (not as fast)
-selective or artificial breeding: farmers selectively breed animals with the best traits
Darwin’s idea: natural selection
-variation exists within populations
-some variations are favorable  allows species to reproduce and gives them the potential to pass on
helpful traits
-not all young produced in each generation survive
-individuals that survive and reproduce are those with favorable variations = survival of the fittest
-survival of the fittest-organisms that inherit the “best” traits are the ones that survive
-they may pass their “good” genes on to the next generation
evidence of evolution
fossils
-provide evidence of what earlier forms of the same animals or plants looked like
-can be used to show relationships
-the fossil record is often incomplete  not likely that organisms will become fossils
biogeography
-two organisms that live in different geographic locations have similar traits
-ex: the flying squirrel lives in North America and the sugar glider lives in South America, but they are
very similar
morphology
-organisms that are related often demonstrate similarities
-ex: bears and wolves are more similar to each other than lizards, frogs and fish are more similar to each
other than beetle
homologous structures
-structures that are similar in structure, but serve different functions
-implies relatedness
-ex: hand vs. bat wing
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vestigial structures
-structures that are inherited but are reduced in size and often unused
-suggests a common ancestry
-ex: leg bones in snakes and ear muscles in humans
embryos
-embryos of related organisms develop in similar ways
-ex: vertebrates
-pharyngeal pouches
-dorsal nerve cord (back)
-notochord (backbone on back)
-post anal tail
biochemistry
-all living things:
-use ATP (energy)
-code genetic traits in DNA
-make proteins with RNA
Variations
-variation: the differences between individual members of a population
-ex: fur coloration, leaf shape, gender, teeth shape
-how do variations occur?
1. genetic recombination- some of the genes are contributed by both parents
2. mutations- changes in nitrogenous bases in DNA that may result in differences in offspring
3. crossing over
4. random fertilization
5. independent assortment
-why is variation important?
-differences within a population allow some of the individuals to survive some of the time under
extreme conditions, while others don’t survive
*remember the whimpogs!! :)
-adaptations: an inherited trait that increases a population’s chance of survival and reproduction in a
particular environment
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Taxonomy and Evolution
The species concept
-taxonomy: the theories and techniques of describing, grouping, and naming living things
-basically, taxonomy = scientific classification
-species: interbreeding populations of organisms that can produce healthy, fertile offspring under
natural conditions
-to be considered a species, the organisms must:
-be able to bread with one another and produce fertile offspring in nature
-ex: horse = a species
mule = not a species because it’s sterile
-humans = a species
-individual members of a species may look different from one another = variation
-natural selection acts on variation, resulting in changes in species or the evolution of new species
-variations in a population include:
-polymorphism- when two or more forms, or morphs, exist in the same population
-ex: male and females of the same species
-geographic variation- when a species occupies a large geographic range that includes distinct local
environments
-individual variation- occurs in all populations of organisms that reproduce sexually
-members of species may interbreed occasionally
-if the two groups fail to produce a significant number of hybrids, they remain separate species
-species remain separate from one another in three ways
1. potential mates don’t meet
-grizzly bear and polar bear: they live in different habitats and don’t meet in the wild
2. potential mates meet and don’t breed
-a giraffe and an ostrich meet but are too different to mate
3. potential mates meet and breed but don’t produce fertile or viable offspring
-a dog and a coyote mate but don’t produce fertile offspring
-the species concept doesn’t apply to organisms that don’t reproduce sexually
Classification and Homologies
The importance of scientific classification
-it benefits public health and helps with disease control
-it plays a role in ecology and helps preserves ecosystems
-the ecosystems that sustain life depend on the millions of species
-it is key to our understanding of living things and the unity of life
-taxonomists can identify weeds and help develop wild species of plants into new crops
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Homologies
-taxonomists group species according to how closely they think the species are related by ancestry
-taxonomists use many characteristics to classify organisms: structure, biochemistry, behavior, genes
-stable characteristics are the most useful, like structures such as skeletons (in animals) and flowers
(in plants) vary less within a species than size and color do
-classification focuses on structures that indicate a related evolutionary ancestry, not just similarity
- homologies: these structural resemblances and similarities that result from evolution from a common
ancestor
-ex: bat wings and human arms and whale flippers are similar in bone structure these limbs are
homologous
-analogies: structures that are similar in appearance and function but are not the result of shared
ancestry
-ex: insect wings have a very different structure than bird wings and contain no bones at all  the
wings of birds and insects have the same function, but don’t reflect a shared ancestry between them
Types of homologies
-anatomical (structural) homologies are very important
-they are easy to observe in organisms and fossils
-fossils are the only evidence we are ever likely to have of extinct species. An extinct species may be
the ancestor of a living one. Knowledge of past organisms helps us determine the relationships of
living ones.
-chemical homologies, like similarities in structures of cellular polymers, are also evidence of close
evolutionary relationships
-the sequence of amino acids in a protein molecule or nucleotide bases in DNA in organisms from
before and now have produced new evidence of evolutionary history
-chemical homologies are harder to identify than anatomical homologies
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Classification Systems
Aristotle
-one of the 1st classification systems
-he classified living things into two groups: plants and animals
-he classified plants by size: trees, shrubs, or herbs
-he classified animals by geographic location: land, water, or air
Linnaeus’ Classification System
-carolus Linnaeus “latinized” his name, karl linnea
-based on homologies and similarity of structure
-physical
-DNA
-used binomial nomenclature: a two-word specific name (Genus – species)
-used latin: understood all over the world
-the name is italicized when typed and underlined when written, and only the first word is capitalized
-it standardized scientific communication
-overcomes the use of common names
-taxon: the different groups that scientists classify organisms in based on common characteristics
-there are 7 taxons (not including domain)
Levels of Classification
domain
-prokaryotes or eukaryotes
kingdom
-a group of related phyla
-there are 5 kingdoms today
phylum
-a group of related classes
-if an animal has a backbone, it is part of the phyla chordata
-many botanists group organisms into divisions instead of phyla
class
-a group of related orders
-ex: birds = aves
order
-a group of related families
family
-a group of related genera
genus
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-a group of related species with many similar characteristics
species
-most specific group
-as you go from species to kingdom, the organisms that are grouped together share fewer
characteristics at each succeeding level
-at the species level, individuals are so alike they can interbreed
-organisms at the kingdom level share only a few common characteristics
-as you move from largest taxon to smallest taxon:
1. there are fewer organisms
2. they have more common characteristics
-the species describes the genus name
-ex: grizzly bear = ursa horriblus = horrible bear
Three Ways to Classify Systems
-taxonomists have always relied heavily on anatomical similarities and differences among organisms
-ex: birds are divided into orders partly based on differences in beaks and claws
-when microscopes and other tools became available, taxonomists were able to use other kinds of info
-growing collections of fossils provided clues about early ancestry
-biologists would examine many organisms and try to judge which characteristics were most useful for
classifying them, called orthodox classification
-ex: grouping birds into orders
-the method phonetics compares organisms on the basis of as many characteristics as possible. The
taxonomist then gives each pair of organisms a similarity score based on the number of traits they share.
-this method gives equal importance to all characteristics
-all members of a group may not share a specific characteristic, like the form of their beaks or feet
-does not consider other evidence, like fossils that may represent shared ancestors
-is most useful in classifying large groups of similar organisms, but is no longer popular
-cladistics is a simpler system that does consider ancestry
-it groups species according to ancestry and homologous characteristics not found in other
organisms
-cladists assume that each group has an ancestor that other species don’t share
-ex: all mammal species have milk glands, but no other organisms do  therefore, all mammals
must be descended from a species that has no other living descendants
-the mammals form a clade, or branch, on a diagram of the history of the animals
-cladistics is popular because it states exactly which features define each clade
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Five Kingdoms
-as you move through the classification system from species to kingdoms, each level includes more
types of organisms
-the more types of organisms that a category includes, the less similar they are
1. Monera/bacteria
-prokaryotes: unicellular or colonial
-reproduction by simple cell division
-include heterotrophs, photoautotrophs, and chemoautotrophs
-many types change their form of nutrition in response to changes in the environment
-bacterial taxomony relies heavily on comparisons of DNA sequences and the composition of cell
walls and membranes
-divided into two groups:
1. eubacteria
2. archaea
2. Protista
-mostly microscopic unicellular eukaryotes
-are descended from bacteria
-far more diverse than other kingdoms
-vary greatly in structure, reproduction, and lifestyle
-some switch from one form of nutrition in response to environmental conditions
-examples: algae (photoautotrophs), protozoa (swimming or creeping heterotrophs), slime molds
(funguslike protists), and others
3. Plantae
-photoautrophs
-multicellular eukaryotes
-developed from embryos
-have cellulose-containing cell walls
-their cells contain chloroplasts
-the bulk of the world’s food and much of its oxygen are derived from plants
-examples: mosses, ferns, conifers, and flowering plants
4. Animalia
-heterotrophs
-multicellular eukaryotes
-developed from embryos
-ranges in many sizes, these organisms are the most diverse in form of all of the kingdoms
-most reproduce sexually
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-anthropods: animals that have exoskeletons and jointed legs, and may be the majority of all
multicellular species
-vertebrates: animals with a backbone
-most members of this kingdom are motile, or capable of locomotion, and have senses and nervous
systems
5. Fungi
-most are decomposers
-some heterotrophs that absorb small molecules from their surroundings through their outer walls
-most are multicellular (with the exception of yeast)
-have cell walls composed of a thought carbohydrate called chitin
-they reproduce by forming spores, either sexually or asexually
-examples: yeasts, molds, bracket fungi, and mushrooms
Classification and Change
-taxonomic classification is not fixed
-it depends on the interpretation of the evidence
-biologists sometimes disagree about where to classify organisms
-as we gain more information, the relationships among organisms become more complex
-new knowledge often requires changes in the way we group organisms
-linnaeus’s original system had only two kingdoms, plants and animals
-as we gained more information, biologists suggested more kingdoms
-electron microscopes helped us gain information on prokaryotes and eukaryotes
-taxonomists added the kingdom monera
-whittaker recognized that fungi are very different from plants
-created the kingdom fungi
-Carl Woese found that Archaea are as different from other bacteria as bacteria are from eukaryotes
-some biologists don’t accept the 5 kingdom system
-classification systems reflect our knowledge of the living world
-classification helps us think more clearly about the great diversity that surrounds us
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