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