Chapter 11 Biology 1010 - Evolution and Its Processes

Darwin

* Took five-year voyage (1831-1836) around the world helped Darwin make observations that would lead to his theory of Evolution
* Evolution is idea that Earth’s many species are descendants of ancestral species that were different from those living today

*On the Origin of Species by Means of natural Selection*

* A book made by Darwin in 1859
* Alfred Wallace helped
* Descent w/ modification, evolution by mechanism of natural selection
* As organisms spread into various habitats over millions of, they accumulated diverse adaptations that fit them to specific ways of life in these new environments

Evolution

* Evolution
* Changes in population from generation to generation
* Natural Selection
* A process in which individuals w/ certain inherited traits are more likely to survive + reproduce than others who do not have those traits
* Adaptations
* An inherited characteristic that enhances an organism’s ability to survive and reproduce in a particular environment

Evolution Occurs Within Populations

* A population is
* Group of individuals of same species
* Living in the same place at the same time
* Populations may be isolated from one another
* Individuals within populations may interbreed
* We can measure evolution as a change in inheritable traits in a population over generations

Evolution Occurs Within Populations Contin.

* **Microevolution** change in relative frequencies of alleles in a gene pool over time
* **Gene Pool** is total collection of genes in a population at any one time
*  Hardy-Weinberg principle
*  Mutation and sexual reproduction produce the genetic variation that makes evolution possible
*  **Mutations** are
* Change in nucleotide sequence of DNA
* Ultimate source of new alleles

Mechanism of Microevolution

* Three main causes of evolutionary change -
* **1.)** Natural Selection
* Only natural selection consistently leads to adaptive evolution
* **2.)** Genetic Drift
* Genetic Drift is a change in gene pool of population due to chance
* In small population, chance events may lead to loss of genetic diversity (bottleneck effect and founder effect)
* **3.)** Gene Flow
* Movement of individuals or gametes/spores between populations

Genetic Drift

* **Bottleneck Effect**
*  Occurs when an event/catastrophe drastically reduces the number of organisms in a population
* Variation in that population may also be reduced, changing the allele frequencies within the population
* **Founder Effect**
* Occurs when combinations of rare alleles occur @ higher frequency in a population that has been isolated from a larger population
* FLDS fumarase deficiency example

Speciation

* Is process by which one species splits into two or more species
* Every time speciation occurs, diversity of life increases
* Macroevolution

Allopatric Speciation

* Populations of same species are geographically separated, isolating their gene pools
* Isolated population will no longer share changes in allele frequencies caused by –
* Natural Selection
* Genetic Drift
* Mutations

 

Sympatric Speciation

\
* Occurs when a new species arises within same geographic area as a parent species
* Many plants species have evolved by polyploidy in which cells have more than two complete sets of chromosomes
* Sympatric speciation can result from polyploidy
* Within a species (by self-fertilization)
* Between two species (by hybridization)

Isolated Islands often Showcases of Speciation

* Evolution of many diverse species from a common ancestor is adaptive radiation
* Darwin’s finches
* Share many finchlike traits
* Differ in their feeding and their beaks specialized for what they eat
* Arose through adaptive radiation

Study of Fossils

\
* Provides strong evidence for evolution
* Fossil Record
* Sequence in which fossils appear within strata (layers) of sedimentary rocks
* Paleontologists
* Scientists who study fossils
* Many fossils link early extinct species w/ species living today
* Example – evolution of whales from a group of land mammals

Geology

* Organisms of evolved in a historical sequence
* **o**  Oldest known fossils
* About 3.5 billion years ago
* Prokaryotes
* **o**  Oldest Eukaryotic Fossils
* About 2.5 billion years ago
* Multicellular Eukaryotic Life
* About 1.5 billion years ago

Biogeography

* Distribution of species
* Where they came from
* Suggested to Darwin that organisms evolve from common ancestors
* Darwin noted that Galápagos animals resembled species on the South American mainland more than they resembles animals on islands that were similar but much more distant
* Galápagos species evolved from animals that migrated from South America

Comparative Anatomy

* Is the comparison of body structure in different species
* **Homology** is the similarity in characteristics that result from common ancestry
* **Homologous Structures** have different functions but are structurally similar because of common ancestry
* Like human arm, cat paw, whale flipper, and bat wing show homology

Anatomical Evidence

* **Vestigial Structures** unused structures that reveal common descent
* Whales and snakes all show vestigial bones related to four-legged animals
* Humans have a tailbone but no tail

Molecular Biology

* Reveals evolutionary relationships
* Comparing DNA and amino acid sequence between different organisms
* These studies indicate that –
* All life forms are related
* All life shares a common DNA code for proteins found in living cells
* Humans and bacteria share homologous genes that have been inherited from a very distant common ancestor