ch 12 Flashcards
Lamarck believed that
evolution occurs as structures develop through use, or disappear through disuse, and that these acquired characteristics are passed to offspring.
Darwin realized that
individuals that have characteristics that give them an advantage in their environments are more likely to survive and reproduce. Thus, these characteristics will increase in a population and over time and the nature of the population will change.
Darwin’s experience in breeding domestic animals, his observations during the voyage of the Beagle and Mathus’s ideas on population led Darwin to develop
the theory of evolution by natural selection.
Darwin did not publish his ideas about natural selection until similar ideas were presented to him by
Alfred Russell Wallace. Today, Darwin’s theory is widely accepted.
Microevolution
is change within a species.
Macroevolution
is change among species.
Although incomplete, the fossil record contains
striking evidence of evolution.
A family tree shows
how organisms are related through evolution. Each branch point in the tree indicates a common ancestor.
DNA and other molecules contain
a record of evolution.
Homologous structures provide evidence of
common ancestry.
Vertebrate embryonic development indicates that
new genetic instructions have been layered on top of older ones.
Gradualism
is the model of evolution in which change occurs gradually over time.
Punctuated equilibrium
is the model of evolution in which change occurs in spurts separated by long periods of equilibrium.
Experiments show that microevolution has occurred within populations of the
European peppered moth.
Balancing selection
maintains an allele in a population when the environment acts on the allele in opposing ways.
Directional selection
causes an allele to become either more or less common.
Lamarck
through use or disuse “acquired characteristics” passed on to generations (1809)
Charles Darwin
at age 22, sails aboard HMS Beagle as unpaid naturalist to collect and study plant and animal specimens, study geology, climate and peoples of the world.
INFLUENCES on voyage:
- Read Lamarck’s theory while sailing. Got him thinking about the “how” of evolution.
- Found: fossils of armadillos that looked similar to present day armadillos
Wondered: Why species in same place similar yet different
Reasoned: One species gave rise to another
• Found: Galapagos plants and animals similar to nearby South America AND not similar to other similar but distant tropical island species.
Wondered: Why wouldn’t a divine creator create similar species on ALL similar tropical islands around the would ? Why Galapagos species resembled nearby South American species instead?
Reasoned: They migrated from nearby SA and then evolved due to different conditions of the different islands.
INFLUENCES at home:
• Read Thomas Malthus’s paper.
Thomas Malthus’s points:
Unchecked, a human population would grow at geometric rate while food supply would grow at
arithmetic rate.
Darwin realizes Malthus’s principle applies to all species – every organism has potential to have offspring BUT not all do because of pressures.
• Ran his family’s farm - farmers “artificially” select which organisms in this year’s crops or herds will get to live & reproduce (to pass on the traits the farmer wants).
Elements of Natural Selection:
- Must have: Phenotype variation in a population - if all members of a population are the same then none will have worse (or better) traits than others.
- Must have: A NEW pressure selects “for” or “against” certain traits - if there is no new/different pressure than there’s no reason a population will change
- These two “must have” conditions result in: Those with better traits survive because they have better traits….
- …which results in: those that survive get to reproduce (in larger numbers than those that don’t survive as well)…..
- …which results in: those that survive and reproduce and, therefore, pass on their (better) traits to the next generation.
Variation
exists within genes of every species.
In a specific environment some individuals of a species are better suited to
survive and breed.
New species
replace old species over time.
Fossil evidence shows clearly that
species living today evolved from earlier species.
In 1844 (8 years after return)
Darwin finished his theory and book manuscript but only showed it to a few friends because of the criticisms other theories that challenged creationism had received.
In 1858,
only after reading Wallace’s paper did he decide to publish (along with Wallace)
Population
group of individuals in same species, same area that interbreed.
Microevolution
the process of natural selection causing change within a population over time.
Macroevolution
the process of natural selection causing change among species over time.
Fossil
preserved or mineralized remains or traces of an organism. Formed when organism is buried by fine sediment before it can decay.
Paleontologists
study fossils.
Paleontologists use two types of information to relate one species to another:
Morphology (shape) - the closer one species resembles another the more likely the are closely related.
Time (when the organism lived) - Initially measured or valued in layer of rocks - the deeper, the older. Now measured by radiometric dating of the rocks in which the fossils are embedded, comparing ratios of amounts of radioactive isotopes of elements found in the rock.
Family tree
shows species relationships over time.
Common ancestor
species from which two or more species evolved.
Trends of the 3.6 billion years:
In addition to suggesting one species may have evolved from another, the overall picture of life on earth, as documented by fossil record reveals the extent and nature of change over time, indicating that, as time passed……
life on earth became more and more diverse (more and more species) and life got more and more complex
Vestigial structures
structures which have little or no present function but show evidence of evolutionary past.
Vertebrate embryo similarities
indicates shared common ancestry where new genetic instruction layered over older genetic information.
Similarity in nucleotide sequences in DNA and Amino Acids sequences in protein indicate and supports
evolutionary relationships in family trees. As species evolve genetic instructions change as well.
Protein Amino Acids (generated from mRNA, DNA) also changes.
The closer related species are to one another (more recently diverged from a common ancestor) the closer their amino acid sequences, mRNA and DNA are (less time to accumulate mutations).
The rates of evolution:
Gradualism
Punctuated Equilibrium
Both theories supported by fossil evidence.
Gradualism
change among species occurs gradually over time.
Punctuated Equilibrium
periods of rapid speciation alternating with periods of little or no change.
2 things that precede/enable spurts of rapid speciation:
- Mass extinction - elimination of many species opens up “jobs” in a wide variety of habitats/ecosystems with a wide variety of selective pressures selecting for a wide variety of organisms
- A radically new type of life form evolves - these new type of organisms rapidly diverge/speciate taking jobs that were always there but could not have been taken by any (usually less-capable) organisms before.
Example: Eukaryotes with organelles that perform a wide variety of specific functions enable these organisms to take more advanced “jobs” in a wide variety of habitats/ecosystems with a wide variety of selective pressures selecting for a wide variety of organisms
Five elements of Natural Selection:
All species have genetic variation
Environment presents survival challenges
Competition within a species results in better suited surviving
Individuals better able to cope leave more offspring
Characteristics of those better suited to an environment (passed on) tend to increase over time.
Sickle cell anemia:
Recessive allele (1/100) – fully expressed in homozygous recessive – lethal.
Co-dominant expression in heterozygous (1/5) (normal and sickled cells present) In malaria areas of central Africa heterozygous individuals have more resistance to malaria and live.
Sickle Cell allele in non-malaria areas:
Directional selection
Directional selection
natural selection forces eliminates (or favors) one end of a phenotype spectrum or one types of alleles. Homozygous recessive (and it’s alleles) eliminated by Sickle cell disease. Homozygous dominant and heterozygous (and their alleles) survive and pass on alleles.
Sickle Cell allele in malaria areas:
Balancing selection
Balancing selection
natural selection that eliminates (or favors) both ends of a phenotype spectrum or both types of alleles.
Homozygous (both genotypes)
individuals selected against. Sickle cell individuals die of Sickle Cell and homozygous non-sickle cell die of malaria.
Heterozygous
selected in favor - survive both.
Divergence
accumulations of differences between, populations, and species)
Divergence within a population leads to
speciation (development of separate species).
In order for two species to diverge from one two factors must be present:
- Two populations of the one species must be isolated from one another - so they are not interbreeding and mixing their DNA
- The two populations face different environmental pressure - that selects for different traits (and DNA that codes for them)
The most common type of isolation is
geographical (physical)
Ecological races
populations of a species living in (and adapting to) specific environment.
New species can’t interbreed with old.
Types of reproductive isolation:
Geographical isolation Ecological Temporal Behavioral Mechanical Reproductive failure
Geographical isolation
different area.
Ecological
different habitats, hybrids not suited to either.
Temporal
reproduce at different time.
Behavioral
not attracted.
Mechanical
not physically capable.
Reproductive failure
infertile offspring.
Homologous (similar) structures, like similar bone structure in the limbs of vertebrates, indicate
a shared common ancestry.
