Mrs. Degl

Intro to Evolution

Evolution – The process of change over time

The Theory of Evolution suggests that existing forms of life on Earth have evolved from earlier forms over long periods of time.

Mrs. Degl

Evidence

Scientists estimate that the Earth is at least as old as it’s oldest rocks, which are 4.6 billion years old. Radioactive dating gives us the age of the oldest rocks.

While studying the rocks of the planet, scientists have found millions of fossils (the remains or traces of organisms that no longer exist). By studying the rocks and fossils, scientists have developed a picture of the changes that have occurred on the Earth, and with it’s living organisms, throughout time.

Mrs. Degl

Mrs. Degl

Dunkleosteus (30 ft long; bony skull shown here is about 1 meter high)Extinct at the end of the Devonian.What is this?

Mrs. Degl

• Most fossils are found in sedimentary rock that was formed at the bottom of water.

• Sediments are formed when water flows over land and wear away (erodes) the land.

• These sediments then settle to the bottom of the water (ocean, river, lake).

• They eventually harden (due to the pressure on them) into rock.

How do fossils form?

Mrs. Degl

The Fossil Record

The earliest fossils found date back to 3.5 billion years ago. These are fossils of bacteria. Fossils can be found in sedimentary rock; preserved in ice, tar or amber; and sometimes completely mineralized (petrified) bones can be found in the ground as well.

The Principle of Superposition states that all rock layers (strata) are older than the rock layers above them. So, older fossils are below younger fossils.

Fossils in the upper strata are usually more complex than what is below them, but also resemble them. This suggests that there is a link between recent and older forms of life.

Mrs. Degl

Earth’s Geologic History There are 2 ways to reconstruct the Earth’s past:

1. Absolute Dating: - placing rock layers/fossils in proper order based on their actual ages. You can assign each layer an age in years. This is done with radioactive elements, like carbon.

2. Relative Dating: - placing rock layers/fossils in proper order based on their order of formation (Law of Superposition). You just know which ones are older and younger than the others. You do not know the exact age in years, of each layer.

Mrs. Degl

Mrs. Degl

Observations that support the Evolution Theory have been made from studies in:

1. Comparative Anatomy (bone structure study)

2. Embryology (embryo study)3. Cytology (cell study) 4. Biochemistry (similar DNA, and

enzymes).

Mrs. Degl

•Evidence supports that similarities of basic structures exist between different organisms.•Homologous structures are similar anatomical parts found in different organisms.•The presence of these homologous structures suggest that these evolved from a common ancestor.

Comparative Anatomy

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Comparative Embryology Common ancestor?

Mrs. Degl

Theories of Evolution attempt to explain:

1. Similarities and differences among species

2. Adaptations

Adaptations are a major component to evolutionary theories. Adaptations are features which make a species better suited to live and reproduce in its environment.

Mrs. Degl

•For many centuries many people believed in the concept of spontaneous generation, the creation of life from organic matter. •Louis Pasteur ended the debate with his famous swan-neck flask experiment, which allowed air to contact the broth. Microbes present in the dust were not able to navigate the tortuous bends in the neck of the flask. This cannot happen!

Spontaneous Generation Theory

Mrs. Degl

Lamarck’s Theory…Also called “use and disuse”… Proven NOT TRUE!!... He thought presently used structures were better developed and passed on…and those not used disappeared.

Mrs. Degl

• While on the Galapagos Islands Darwin studied finches.

• He noticed that the finches beaks on all of the islands were slightly different and Darwin wondered why.

• He proposed that evolution occurred as a result of NATURAL SELECTION.

NATURAL SELECTION THEORY

Mrs. Degl

Mrs. Degl

Mrs. Degl

Included in Darwin’s Natural Selection Theory

were six main ideas:

1. Overpopulation 2. Competition 3. Survival of the Fittest

4. Natural Selection 5. Reproduction 6. Speciation

Mrs. Degl

Overpopulation

• Within a population, there are more offspring produced in each generation than can

possibly survive.

Mrs. Degl

Competition• Natural resources (food,

water, and space) are limited.• Because there are many

organisms with similar requirements, there must be

competition between them for the resources needed to

survive.

Mrs. Degl

• Variations among members of a population make some of them better adapted to the environment than others.

• It is generally the best-adapted individuals that will survive. The ones not very well adapted will die off.

Survival of the Fittest

Mrs. Degl

Natural Selection•The environment is the agent of natural selection.

•Meaning, in an environment experiencing a particularly cold period, the species variation that has the thicker fur will most likely survive.

•In this case, their variation (thicker fur) is more helpful for survival and the majority of that population will have thick fur.

Mrs. Degl

Reproduction•All species will reproduce.•The species with the best variation will have a have a higher offspring rate, because there would be more of them around to mate.•What results is the better adapted trait gets passed down to the future generations while the less successful variation gets phased out over time.•An example is how the thicker furred animal would produce more offspring in the cold period, while the thinner furred animal would not.•This is what causes extinctions.

Mrs. Degl

• The development of a new species occurs as variations or

adaptations accumulate in a population over many

generations

• Ex: caveman present man

Speciation

Mrs. Degl

Wrong Right