Chapter 16

Anaximander (Greek) – believed living things have changed Aristotle (Greek) - believed species to be fixed concurred with Judeo- Christian culture that believes that all living species are static in form and inhabit an Earth that is at most 6000 years (Creationism) George Buffon (French ~1750’s) – Fossil evidence led him to believe that the earth was much older Jean-Baptiste Lamark (early 1800’s) – Believed in the inheritance of acquired characteristics Charles Darwin (English published 1859 The Origin of Species) – Believed in descent with modification (evolution) & common descent Charles Lyell (Scottish, influenced Darwin) – Believed in gradual geological change, not catastrophes Alfred Wallace (English 1850’s) – conceived a theory of evolution almost identical to Darwin’s

Thought that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetimes These traits could then be passed on to their offspring This led to speciation  /?

Englishman born in 1809 Took a trip on the HMS Beagle in 1831 Used his observations of wildlife, mainly in the Galápagos Islands, to develop his theory of evolution

Was impressed by the diversity of living things Observed how plants and animals always seem to be well adapted to their environments Was puzzled that the same grassland species found in Europe are different from the ones in South America and even still different in Australia He gathered many fossils on his trip and was able to compare some with living species while others he had never seen before

Pinta Island Intermediate shell Pinta Isabela Island Dome-shaped shell Rich Vegetation Hood Island Saddle-backed shell Sparce vegetation Hood Floreana Santa Fe Santa Cruz James Marchena Fernandina Isabela Tower

Natural Variation Artificial Selection Struggle for existance Survival of the fittest Natural Selection Descent with Modification

With sexual reproduction and the crossing over of genes, we find natural variation between individuals of the same species

Humans pick the individuals of a species with the desired traits (variations) and then they breed only individuals with the desired trait Done with plants and animals

Darwin thought that a process like artificial selection existed in nature He noticed that all organisms must compete with other individuals of the same species for food, water, living space, etc. (Struggle for existence) He observed that individuals with the natural traits that suited them best to their environment could live longer than other individuals and thus had more reproductive success. (they were more fit)

If an individual has a great reproductive success (has many offspring), then his/her traits will be passed on to many offspring (F 1 generation) If those offspring possess traits that make them better able to compete and reproduce, then those traits will, again, be passed on to the F 2 generation.

Is another name for survival of the fittest Process by which individuals that are better suited to their environment survive and reproduce more successfully. Natural selection results in changes in the inherited characteristics of a population. These changes increase a species’s fitness in the environment *. * Some exceptions usually have to do with sexual attraction between individuals who select their mate based on a trait that does not increase their fitness.

Over long periods, natural selection produces organisms that have different physical structures, behavioural patterns, and occupy different niches from their ancestors. This principle implies that all organisms are related to one another, they are of common descent.

1. Individual organisms in nature differ from one another. Some of this variation is inherited. 2. Organisms in nature produce more offspring than can survive, and many of those that survive do not reproduce. 3. Because more organisms are produced than can survive, members of each species must compete for limited resources. 4. Because each organism is unique, each has different advantages and disadvantages in the struggle for existence.

5. Individuals best suited to their environment survive and reproduce most successfully and therefore pass on their traits. Less successful individuals, die and do not pass on their traits. 6. Species change over time. Natural selection causes changes in the characteristics of a species. New species arise, and others disappear. 7. Species alive today have descended with modifications from species that lived in the past. 8. All organisms on Earth are united into a single tree of life by common descent.

Water carries small rock particles to lakes and seas. Dead organisms are buried by layers of sediment, which forms new rock. The preserved remains may later be discovered and studied.

TurtleAlligatorBird Mammals Typical primitive fish

Structures that have evolved for the same purpose in unrelated species

Modifications of the basic incisor structure. The beaver uses its teeth to chew up branches and the elephant uses its tusks for digging, scraping through bark and fighting.

Skeleton of cartiliage Skeleton of bone Don’t nurse their young Nurse their young Use gills to get oxygen Fill up with air using a blowhole for oxygen No hair Born with hair around their « noses »

Fetal chimpanzeeBaby chimpanzeeAdult chimanzee 3-year old humanAfrican adult maleEuropean adult female

Three main causes of evolutionary change 1. Natural Selection Organism with best reproductive success passes their genes down to subsequent generations 2. Genetic Drift Chance events can cause allelic frequencies to fluctuate unpredictably by reducing population sizes drastically and wiping out alleles indiscriminately (bottleneck effect, founder effect) 3. Gene Flow Migration (tends to reduce differences b/w populations

Sample of Original Population Founding Population A Founding Population B Descendants

Flesh-eating disease

Balancing Selection – when natural selection maintains stable frequencies of two or more phenotypic forms in a population Heterozygote Advantage – Ex. Sickle-cell anemia in malarial regions Frequency-Dependent Selection – Ex. Scale-Eating Fish

Individuals with the less common phenotype will have a selective advantage

1. Selection can act only on existing variations 2. Evolution is limited by historical constraints 3. Adaptations are often compromises 4. Chance, natural selection, and the environment interact

Micro – change in allele frequencies within a population Macro – process by which new species originate