Origins of Diversity11.4

The Diversity of SpeciesResult of the formation of different speciesHow?

A possible explanation: evolution through NATURAL SELECTION

- Proposed by Charles Darwin in 1859 in his book

“The Origin of Species by means of Natural Selection’

Genetic VariationThe basis of natural selectionChanges in the characteristics of a species are

produced by a combination ofRandom genetic mutationsSelection for a particular characteristic which

increases survival and breeding success.

Sexual Reproduction: provides genetic variation within a population reassortment of genes

Selection is then made amongst this variation.

Natural SelectionEnvironment selects individuals with the

characteristics that allow them to survive over other individuals with characteristics that are not suited for the environmental conditions.

Shell ActivityDemonstration.

Selection occurs within the variation of the population

Selected organisms produce more offspringMore may survive to reproductive ageMay be more attractive to opposite sex

Determining RelatednessOne goal of taxonomy: to determine the

evolutionary history of groups of organisms. Use different types of evidence to study

evolutionary relationships. AnatomyDevelopmentBiochemistryDNARead pages 400-403 on these topics. Briefly

summarize how each type of evidence is used to study evolutionary relationships.

PhylogenyThe evolutionary history of organisms. The ‘root’ represents the oldest ancestral speciesForks represent points in past at which ancestral species split

into two new species. Primitive characteristics: general characteristics that are shared

by all species evolved from it Determine the Order Ex// Artiodactyla all have even number of hooved toes on each

hindfoot and have specialized teeth and digestive systems adapted to eat plants. 150 members: goats, deer, cattle, camels, pigs, etc.

Derived characteristics: new additional features giving rise to new species.

With continuing evolution, further new derived characteristics are added.

CladisticsClassification scheme based on phylogeny.

Each group of related species has one common ancestor, and organisms retain some ancestral characteristics and gain some unique derived characteristics as they evolve and diverge from the common ancestor.

CladogramBranching diagram that resembles a

phylogenetic treeCan be used to test alternate hypotheses.

Example:Three species share a primitive characteristic

from a common ancestor. Which species diverged first?Which are more closely related?

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