Natural selection

Charles Darwin• Born February 12, 1809 Shrewsbury England• Medical School (1825-1827)

– Darwin is 16 Years Old

• Cambridge (1827-1831) Clergyman • Naturalist of H.M.S. Beagle• Beagle Departs from Plymouth, England

on December 27, 1831– Darwin is 22 Years Old

H.M.S. Beagle

Route of the H.M.S. BEAGLE

timeline• January 1832 Santiago, Cape Verde Islands “Seashells”• April 1832 Rio de Janeiro, Brazil “Entomological Specimens”• August 1832 Patagonia Coastline “Useless Junk (Fossils)”• March 1833 Falkland Island, Port Louis “Comparing Fossils”• September 1835 Galapagos Islands, “Discovering Diversity”• October 1836 Falmouth England, “Journey Ends” 4Y9M5D• March 1837 London Zoo “Discovery of Darwin’s Finches”• November 1859 Published “Origin of the Species”• 1930’s-1940’s Evolutionary Synthesis “Mendel and Darwin”

Theory of Natural Selection

1. Organisms produce more offspring than can survive.

2. In any given population, variations exist.

3. Individuals with certain “useful” or beneficial variations survive and pass on their variations to the next generation.

4. Over time, offspring with “beneficial” variations will make up most of the population.

Natural Selection

Darwin used his collections and observations to identify a mechanism for change in populations.

Darwin called this mechanism:NATURAL SELECTION

Natural SelectionScience’s “best

guess” on how populations change over time.

Natural Selection is based on the following scientific evidence.

Structural Adaptations

Physiological Adaptations

Fossils

Anatomy

Embryology

Biochemistry

Structural Adaptations

Structural adaptations are changes in an organism’s appearance

Structural Adaptations

usually develop over a long period

of time

• Defensive Adaptations

• Large Teeth and Claws, Speed and agility, chemical

• Protective Adaptations

• Camouflage, Mimicry, Speed, Chemical, Quills, Spines

• Specialized• Height, Strength,

“Specialized Anatomy”

Physiological Adaptations

Changes in an organism’s metabolic processes.

Can occur over a relatively short period of time.

• Examples– Bacteria– Pesticides– Herbicides– Symbiotic

Relationships (Clown Fish and Sea Anemone)

FOSSILSFOSSIL EVIDENCE:• Provide record of

early life

• Show how changes occurred within most populations and species.

• FOSSIL SHORT COMINGS– Incomplete for many

species – Inferences [However, DNA

can support these inferences]

ANATOMYCONVERGENT

EVOLUTION

Organisms share same function, but not the same form, come from different ancestral lineages.

• Analogous Structures– Similar structural functions but

do not share a common evolutionary origin.

• Similar in function but not arrangement

– Insects vs. Birds

ANATOMYDIVERGENT EVOLUTION

Species that were once similar

• Homologous Structures– Structural features with a common

evolutionary origin• Can be similar in arrangement and

function.– Forelimbs of human, cat, whale, bat

• Vestigial Structure– Body structure in a present day

organism that no longer serves its original purpose.

• Feature is still inherited, although it no longer serves it’s purpose.

– Eye balls present in blind cave salamander

Embryology• Early Embryonic development, all

embryo’s have a tail and pharyngeal pouches.

Biochemistry• Organisms share same

biochemical molecules

– DNA, ATP, ENZYMES, AMINO ACID SEQUENCE

• Organisms that are biochemical similar have fewer differences in their amino acid sequence and are believed to be more closely related or share a common ancestor.

• Phylogeny: Construction of “family trees” using DNA and RNA

THE EVIDENCE• Scientist use:

– Adaptations• Structural• Physiological

– Fossils– Anatomy

• Micro and Macro– Embryology – Biochemistry

• DNA, RNA, Amino Acids

Applying Natural Selection• SPECIATION: Process in which a new species arises

from a formerly interbreeding population.– Cause

•Geographic Isolation•Reproductive Isolation

– Rate•Fast—Punctuated Equilibrium

» Periods of speciation occurs quickly within a long period of genetic equilibrium.

•Slow—Gradualism» Species originate through a gradual change of

adaptations.

Applying Natural Selection• Populations, Not Individuals, Evolve

– Variations arise from mutations– Alleles represent the genetic variation in a

population– The Gene Pool is the all of the different

alleles in a given population.– The percentage of any one allele in the

gene pool is called the Allelic Frequency.– If the frequency of an allele remains

constant we refer to that as Genetic Equilibrium.

Applying Natural Selection:Directional

SelectionNatural Selection Favors OneExtreme Variation of a Trait

Example:Birds with varying sizes of beaks, after a drought, the large beak birds have selective advantage

Applying Natural Selection:Disruptive SelectionIndividuals with either extreme traitare selected for.

Example:Tourists in the desert like to pick up a souvenir from their travels, they pick up the medium spine cactus.

Leaving the “homelier” low spine and avoiding the “prickly” high spine cactus, both of which have the selective advantage.

Applying Natural Selection:Stabilizing SelectionNatural Selection Favors averageindividuals in a population.

Example:Birth weight in humans is highly variable, however, a child that is of average weight has a higher chance of being born and of good health, as to mature and reproduce. Nature selects against the extreme phenotypes.

Natural Selection is currently the best theory scientists have to explain the vast diversity of life on Earth and how populations change over time. In science, nothing can ever be proven as fact, there are no facts in science, only “best guesses”. These best guesses are based on current, verifiable, and testable evidence. We call a collection of evidence that fails to disprove a hypothesis—a theory. In fact, science can only be used to disprove not prove anything.