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EVOLUTION AND DARWIN
Charles Darwin
Darwin is considered the father of evolution theory.
He proposed the ideas of both natural and artificial selection and wrote the book On The Origin of Species
Darwin the Naturalist
Darwin at age 22 took a job as a naturalist and sailed the world recording observation of many animals, trees, and fossils.
He noticed many organisms, though geographically separated, had some common similarities
Darwin’s Theory
Darwin’s observation in the Galapagos islands were extremely important.
He noticed that many of the island had the same types of animals, but all were slightly different, and those differences helped them to better survive the conditions particular to those islands
Darwin’s Theory
The finches Darwin noticed helped him formulate his ideas of evolution
He noticed that they were all similar but had different beak sizes
Darwin’s theory
Darwin discovered that finches with big beaks can eat big nuts, and those with small beaks eat small nuts
He noticed during a rainy year, nuts would grow big and birds with big beaks were abundant
Likewise, he noticed finches with small beaks were present during drought years where seeds were quite small
Darwin’s theory
Based on his observations he came up with the theory of natural selection
The theory of natural selection is the idea that organisms that are better adapted to their environment survive and reproduce more than those who aren’t adapted well…this leads to a change in populations over time (evolution)
Natural Selection
For the theory of natural selection to be correct 5 things must hold true
Natural Selection
1. Struggle for existence The amount of offspring generated through
reproduction exceeds the population size that the environment can support. So, not all individual in the population will contribute to an equal number of offspring in the next generation.
The ones that are best adapted contribute more by better surviving and consequently reproducing.
Organisms that die or do not mate don’t pass on their traits (through genes)
Natural Selection
2. Individuals vary with phenotype There are variations with aspects of
organisms, either in body part or behavior, within a population.
ie… blond hair vs brown hair, tall and short, fast and slow, etc
Natural Selection
3. Inheritance When organisms reproduce, their traits are
passed down to their offspring to some extent
Natural Selection
4. Some Phenotypes are better adapted Certain phenotypes are better suited to the
environment of the organisms. The better suited organisms will have a better chance of survival and reproduction
Natural Selection
5. Consequently, Adaptation Evolve As a result of steps 1-4, total populations
tend to evolve toward the phenotypes that are better adapted to the environment
Sexual Selection
Is the process by which traits, even harmful ones, that increase the chance of an animals reproduction are selected for. If they are more likely to reproduce, they
will pass on this trait…even if harmful for survival
Artificial Selection
Is selectively breeding organisms with specific traits in order to produce offspring with similar traits
All dog breeds were produced this way, larger cattle were selected this way, etc
Supports the theory of natural selection
Adaptations
Darwin’s theory of natural selection and evolution explains why animals have various adaptations
An adaptations is a variation that aids an organism’s chance of survival in its environment
Adaptations
Structural adaptations arise over a long time, with natural selection being the driving force
Sometimes adaptations arise out of mutations in DNA Most mutations are lethal, however a small
percentage are beneficial Common types of adaptation are
mimicry and camouflage
Adaptations
Physiological changes can develop rapidly These are changes in an organism’s
metabolic processes
Examples is bacteria resistant to penicillin Used to be a wonder drug and kill most
bacteria, but most bacteria is now resistant
Other Supporting Evidence for Evolution
Fossils Fossils provide millions of
years of different animal records, though incomplete, gives evidence of changes in animals seen today
Embryology Most organisms
development from an embryo is extremely similar both in features and development
Other supporting evidence for evolution
Biochemistry Nearly all organisms share DNA, ATP and many other
similar biochemical molecules and reaction processes Anatomy
Homologous structures—structural features with common evolutionary origins Can be similar in structure, function or both
Analogous structures—body parts of animals that do not have a common evolutionary origin, but share similar function
Vestigial structure—a body structure in a present day organism that no longer serves a purpose
Populations, not individuals, evolve If an organism has a deleterious trait, it
may be unlikely to survive and reproduce The organism is programmed by its genes
and can NOT change the genes nor the trait Rather natural selection acts on a range of phenotypes in a population (and not a single individual)
Gene Pool
Is the combination of all the genes in one population put together
The percentage of any one gene in the gene pool is called the allelic frequency
Genetic Equilibrium
This is achieved when the allelic frequencies are not changing (are stable) over many generations and hence are NOT EVOLVING
Genetic drift is a term used when a population is no long in equilibrium and instead is favoring (or drifting) towards a higher proportion of a specific allele Its effect is magnified by small populations and
immigration into a population
3 types of Natural Selection
1. Stabilizing selection Favors average individuals in a
population
2. Directional selection Occurs when one of the extreme
variations of a trait is favored
3. Disruptive selection Occurs when either extreme of a
trait is selected for
Evolution leads to new species Recall that a species is a
group of organism that can interbreed and produce fertile offspring
Speciation, the evolution of a new species, occurs when similar organisms in a population can no longer interbreed to produce fertile offspring
Speciation
Is enhanced by geographic isolation Physical barriers can prevent populations from
interbreeding and differences in environment can lead to differences in favored traits for natural selection
Is also enhanced by reproductive isolation This is when interbreeding doesn’t occur do to
genes changing and becoming too different to lead to fertile offspring OR behavioral isolation where populations doesn't interbreed due to mating season differences etc.
Theories of evolution
Gradualism—this is the idea that species originate through a gradual change of adaptations over many years
Punctuated equilibrium—this is the idea that speciation occurs in relatively quickly, in short bursts, with long periods of genetic equilibrium in between
Evolutionary Patterns
Divergent Evolution Is the pattern of
evolution where species that were once similar to an ancestral species have become increasingly distinct to specialize for certain niches in the environment
Evolutionary Patters
Convergent Evolution Is the pattern in which distantly related
organisms evolve similar traits to occupy similar roles in the environment