Chapter 4

Read the Core Case Study on Page 82.

Summarize the main ideas and be prepared to discuss.

Scientific evidence indicates that the Earth’s life is the result of … 1 billion years of chemical change to form

cells.

3.7 billion years of biological change to produce the variety of species we have on Earth today.

1 billion years Organic molecules, bipolymers, systems of

chemical reactions Evidence comes from

chemical analysis and measurements of radioactive elements in primitive rocks and fossils

Lab experiments that show how simple inorganic compounds might have reacted to produce amino acids, sugars, and other organic molecules that became the building blocks for proteins, carbohydrates, RNA and DNA.

Followed chemical evolution Uses natural selection Moved from single-celled bacteria to

multi-cellular protists, plants, fungi, and animals.

This phase is ongoing.

Fig. 4-2, p. 84

Variety ofmulticellularorganismsform, firstin the seasand lateron land

Biological Evolution(3.7 billion years)

Chemical Evolution(1 billion years)

Formationof the

earth’searly

crust andatmosphere

Small organic

moleculesform in

the seas

Large organic

molecules(biopolymers

) form in the seas

First protocells form in the seas

Single-cell prokaryotes

form in the seas

Single-celleukaryotes

form inthe seas

Charles Darwin (1809 – 1882) Alfred Russel Wallace (1823 – 1913)

Fig. 4-3, p. 84

Modern humans appear about 2 seconds before midnightRecorded human history begins about 1/4 second before midnight

Origin of life (3.6-3.8 billion years ago)

Age of mammals

Age of reptiles

Insects and amphibians invade the land

First fossil record of animals

Plants begin invading land Evolution and

expansion of life

1859, England, Charles Darwin While on a voyage (HMS Beagle) noticed:

Organisms in one population differ slightly from each other in form, function and behavior.

Some of the differences are hereditary. Proposed a hypothesis for how species change

over time The environment exerts a strong influence over

which individuals survive to produce more offspring.

Some individuals, because of certain traits, are more likely to survive and reproduce than other individuals.

“Can we doubt…that individuals having any advantage, however slight, over others would have the best chance of surviving and of procreating their kind? On the other hand, we may feel sure that any variation in the least degree injurious would be rigidly destroyed. This preservation of favorable variations, I call Natural Selection.”

--- Charles Darwin

Natural selection is the process by which individuals that have favorable variations and are better adapted to their environment survive and reproduce more successfully than less well adapted individuals do.

Darwin proposed that over many generations, natural selection causes the characteristics of populations to change.

Evolution is a change in the characteristics of a population from one generation to the next.

All populations have genetic variation.

The environment presents challenges to successful reproduction.

Individuals tend to produce more offspring than the environment can support.

Individuals are better able to cope with the challenges presented by their environment tend to leave more offspring than those individuals less suited to the environment.

13 or 14 separate species of finches collected from the Galapagos Islands

All birds are about the same size and color.

Most important differences between species are in the size and shape of their beaks.

Each beak is highly adapted to different food sources.

Large beaks – Crush seeds in beaks

Narrow beaks – Eat insects

Short, stubby beak – Eats seeds and few insects

Sharp beaks – Poke holes in food or pick insects out of cactus

Pale coloured, speckled peppered moth

Dark coloured peppered moth

Peppered moths on tree trunk

Populations – not individuals – evolve by becoming genetically different

1. Development of genetic variability• Occurs through mutations

o Exposure to external agentso Random mistakes

2. Natural Selection

Genetic variability Heritable traits Differential reproduction

An adaptation is any heritable trait that enables an organism to survive through natural selection and reproduce better under prevailing environmental conditions.

Natural selection preserves beneficial adaptations and discards harmful adaptations.

When faced with environmental change an organism has 3 options: Adapt Migrate Become extinct

Genes mutate, individuals are selected, and populations evolve that are better adapted to survive and reproduce under existing environmental conditions.

Interacting species can engage in a back-and-forth genetic contest in which each gains a temporary genetic advantage over the other.

Changes in the gene pool of one organism can cause changes in the gene pool of another organism.

Sometimes the predators surge ahead, at other times the prey get the upper hand.

Sometimes different species can crossbreed to form hybrids that can survive and reproduce.

Some species can exchange genes without sexual reproduction.

A population’s ability to adapt to new environmental conditions through natural selection is limited by its gene pool and how fast it can reproduce.

1. A change in environmental conditions through conventional natural selection only for genetic traits already present in the gene pool.

2. The population’s ability to adapt is limited by its reproductive capacity.

Even when a favorable genetic trait is present in a population, most of the population would have to die or become sterile so individuals with the trait can become dominant and pass the trait on through natural selection.

Most members of the human population would have to die prematurely for hundreds of thousands of generations in order for a new genetic trait to dominate.

Survival of the fittest

Organisms develop traits that they need or want

Evolution by natural selection involves a grand plan of nature in which species can become perfectly adapted.

Evolution through natural selection is about leaving the most descendents

Organisms do not develop certain traits just because they need or want them

There is no master plan leading to genetic perfection.