EvolutionEvolution

Change in allele frequency over time.

Why do we resemble our parents? Hereditary – passing of traits from parent

to offspring Traits – an aspect of an organism that can

be described or measured. DNA - Gene – Chromosome You inherit ½ chromosomes from Mom

and ½ from Dad

Dominant vs. Recessive Dominant – gene that determines

expression of a genetic trait; the trait shows up

Recessive – gene that is overruled by a dominant gene; trait is masked

Genotype vs. Phenotype Genotype – genes of an individual Phenotype – observable traits

Evolution A scientific theory

Well supported testable explanation of phenomena that have occurred in the natural world.

The change in allele (gene) frequencies over time.

Charles Darwin Person credited with our understanding of

evolution.

Took a voyage on the H.M.S. Beagle

Made observations and collected evidence that led him to propose a hypothesis about how life changes over time.

Section 15-1

Figure 15–1 Darwin’s Voyage

Collection of Evidence Each time the ship stopped, Darwin went

ashore to collect plant and animal specimens.

He studied his large collection of specimens and kept a journal with his thoughts and observations.

During his travels Darwin started to believe that he was coming across a scientific explanation for the diversity of life on Earth.

Darwin’s Observations Great Diversity

Patterns of Diversity Plants and animals seemed to be suited for

whatever environment they inhabited. Why do some organisms live in one place but not

in another? (ie. Why no rabbits in Australia? No kangaroos in England?)

Darwin’s Observations Living Organisms and Fossils

Fossils = preserved remains of ancient organisms

Fossils resembled live organisms Why had those species disappeared? Is there a relationship between fossils and living

organisms?

The Galapagos Islands West of South America Although the islands were close together,

they had very different climates. Darwin studied a variety of Galapagos

organisms Finches Tortoises Marine Iguanas Variety of Plant Species

Pinta IslandIntermediate shell

Pinta

Isabela IslandDome-shaped shell

Hood IslandSaddle-backed shellHoodFloreana

Santa Fe

Santa Cruz

James

Marchena

Fernandina

Isabela

Tower

Giant Tortoises of the Galápagos Islands

Section 15-1

Darwin’s Reflections on His Findings

Darwin observed that the characteristics of many animals and plants varied among the different Galapagos Islands.

He began to wonder if these organisms on the different islands had once been a single species.

Key Concept Questions What is evolution?

What was Charles Darwin’s contribution to science?

What pattern did Darwin observe among organisms of the Galapagos Islands?

Why did Darwin think the organisms of the Galapagos Islands were related?

On the Origin of Species Darwin’s book where he published his

ideas regarding Earth’s biodiversity and how life changes over time.

Why do some individuals die early, but not others? Struggle for Existence

Members of each species compete for necessary resources Food Space Etc.

Those that are faster, better camouflaged, or better protected are more likely to survive

Evolution by Natural Selection Survival of the Fittest

Fitness = the ability of an organism to survive and reproduce

Adaptation = inherited characteristics that increase an organisms fitness

Those that are best able to survive and reproduce are the fittest, hence Survival of Survival of the Fittestthe Fittest

Natural Variation &Natural Selection

Natural Variation= differences among individuals of a species

Natural Selection = the differences in survival and reproduction among members of a population.

Evolution by Natural Selection

Over many generations we will see a decrease of animals with unfavorable traits.

Darwin thought there were several factors involved in natural selection The presence of variation Hereditary basis of such variation Tendency for population to increase “struggle for survival” A difference in inherited traits passed on to each generation

Key Concept Questions What is natural variation?

How did we observe natural variation in our “Survival of the Fittest” lab? …in this classroom?

How are artificial selection and natural selection different?

Does natural selection act on an individual or a population?

What makes an organism fit? Can an organism be fit in one environment and unfit in

another? Explain. Provide evidence from lab