chapter 21 Flashcards
(28 cards)
Evidences of Evolution
1. Natural selection can produce evolutionary change 2.Artificial selection shows that selection is an effective evolutionary process 3.Fossil evidence 4.Anatomical evidence 5.Biogeographical evidence 6.Biochemical evidence
Beaks of Darwin’s Finches
-Classic example of evolution by natural selection
-Darwin collected 31 specimens from 3 islands in the Galápagos Islands
Darwin was not an expert on birds
Took them back to England for identification
Told his collection was a closely related group of distinct species
All were similar except for beak characteristics
In all, 14 species now recognized
Modern research has verified Darwin’s selection hypothesis
3 conditions of natural selection
- Variation must exist in the population
- This variation must lead to differences among individuals in reproductive success
- Variation among individuals must be genetically transmitted to the next generation
Peter and Rosemary Grant
To test theory of evolution by natural
selection–
Studied medium ground finch on Daphne Major—30 years
Found beak depth variation among members of the population
Average beak depth changed from one year to the next in a predictable fashion
- Droughts: birds with deeper, more powerful beaks survived better
- Normal rains: average beak depth decreased to its original size
Peppered moths
When the environment changes, natural selection often favors different traits in a species
Adult Biston betularia come in a range of shades
Body color is a single gene
Black individuals have the dominant allele
Rare in the population until 1850s
From that time on, frequency increased to near 100%
J.W. Tutt hypothesized that light-colored moths declined because of predation
Light moths were easily seen by birds on darkened (sooty) trees
Confirmed with separate field studies with a variety of experimental designs
Industrial melanism
- Phenomenon in which darker individuals come to predominate over lighter ones
- Other moths in other industrialized areas showed same trend to darken
- Pollution control resulted in bark color being lighter again
- Light-colored peppered moths now are dominant in the population
Agent of selection?
- Tutt’s hypothesis about the agent of selection is currently being reevaluated
- The current reconsideration of the agent of natural selection illustrates well the way in which scientific progress is achieved
- Hypotheses, such as Tutt’s, are put forth and then tested; if rejected, new hypotheses are formulated, and the process begins anew
Artificial Selection
Operates by favoring individuals with certain phenotypic traits, allowing them to reproduce and pass their genes on to the next generation
This directional selection should result in evolutionary change
Drosophila melanogaster (fruit fly)
Selected fruit flies with many bristles on abdomen
At the start, average number of bristles was 9.5
Chose only those with most bristles to reproduce
86 generations later, average number of bristles had quadrupled to nearly 40
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Agricultural selection
Differences have resulted from generations of human selection for desirable traits, such as greater milk production and larger corn ear size
Domestication
Human-imposed selection has produced a variety of cats, dogs, pigeons, and others
Breeds may have been developed for specific purposes
Dachshunds for badger pursuit
Domestication may lead to unintentional selection for some traits
Attempt to domesticate silver foxes
Chose most docile animals only to breed
Within 40 years, had many of the same behavioral and physical traits as domestic dogs
Are traits for behavior linked to other traits?—color pattern, floppy ears,
shorter legs and tails
Pleiotropy or linkage at work
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Can selection produce major evolutionary changes?
Most scientists think that natural selection is the process responsible for the evolutionary changes documented in the fossil record Some critics of evolution accept that selection can lead to changes within a species, but not the substantial changes documented in the fossil record We have just seen what artificial selection can do in a few thousand years Dog breeds (changes in 10,000 yrs.) would be species if found as fossils—what could selection do in millions of years?
Fossil Evidence of Evolution
Fossils are the preserved remains of once-living organisms—most direct evidence
Rock fossils are created when three events occur
Organism buried in sediment
Calcium in bone or other hard tissue mineralizes
Surrounding sediment hardens to form rock
Process of fossilization is rare event
Aging fossils
Relative dating: position of the fossil in the sediment
Absolute dating: age of fossils is estimated by rates of radioactive decay
Isotopes, like U238, transform at precisely known rates into nonradioactive forms
The rate of decay is known as an isotope’s half-life
Amount of time needed for one-half of the original amount to be transformed
Fossils document evolutionary transitions
Given the low likelihood of fossil preservation and recovery, it is not surprising that there are gaps in the fossil record
Intermediate forms have been found
Oldest known bird fossil is the Archaeopteryx
Clearly intermediate between bird and dinosaur
Possesses some ancestral traits and some traits of present day birds
Recent discoveries—closing major gaps in fossil record
Four-legged aquatic mammal
Important link in the evolution of whales and dolphins from land-dwelling, hoofed ancestors
Fossil snake with legs—descended from lizards
Tiktaalik: a species that bridged the gap between fish and the first amphibian
Oysters: small curved shells to large flat shells
Horse evolution
Modern Equidae are all large, long-legged, fast-running animals adapted to life on open grasslands
First horse was small with short legs—size of large house cats
Wooded habitats
Path to modern horse involved
Changes in size
Toe reduction (4 toeshooves); longer legs
Changes in tooth size and shape (smalllonger; flatter molars for chewing grass); skull strengthen due to chewing
Adaptations to climate change
Grasslands became more widespread
Rates of evolution have varied widely
Anatomical Evidence for Evolution
homology, development, imperfect andvestigial structures
Homologous structures
Structures with different appearances and functions that all derived from the same body part in a common ancestor
The bones in the forelimb of mammals are homologous structures
Different functions, same ancestor structure
Early embryonic development
Strongest anatomical evidence supporting evolution comes from comparisons of how organisms develop
Embryos of different types of vertebrates, for example, often are similar early on, but become more different as they develop
Early vertebrate embryos possess post-anal tail; vestige of this is our coccyx
Early vertebrate embryos possess pharyngeal pouches that develop into
In humans: glands and ducts
In fish: gill slits
Imperfections – some organisms do not appear perfectly adapted to their environments
Workable but imperfect solutions
Most animals with long necks have many vertebrae for flexibility
Geese: 25
Plesiosaurs: 76
Mammals: 7—selection lead to a decrease
in number—not as flexible
Because of the absence of variation in the number of vertebrae, the giraffe (7 vert.) increased the size, to make up for the length of the neck
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Eyes of vertebrates
Photoreceptors face backward
Nerve fibers slightly obscure light and the optic nerve exits a hole at the back of the eye creating a blind spot
Mollusks’ eyes are more optimally designed with no obstruction or blind spot
Vestigial structures
Have no apparent function, but resemble structures their ancestors possessed
Human ear wiggling muscles
Hip bones in boa constrictors
Evolutionary relicts
