What is Evolution????

- It IS a THEORY THEORY that says that present-day life forms developed from earlier, distinctly different life forms- Evidence suggests that life began more than 3 billion years ago

- Started as a single cell

- Evolution is caused by rapid changes in the environment

Evidence Supporting Evolution

1. Fossil Record

- Oldest rocks have little or no fossils

- Life was small single celled bacteria

- Fossils found further up in strata are generally younger and more complex then those found in deepest layers

- Fossils show how life diverged gradually from a common ancestor

- Much like a bush

- Some branches live, others die

- Fossils may also exist in amber, tar, and ice

2. Comparative Cytology- Most life forms have similar cell structures

indicating that they are related to some degree

3. Comparative Biochemistry

- Nucleic acids, their structures and functions are similar in all living things

- The closer the similarities the more closely related the organisms

4. Comparative Anatomy

- Homologous bones and other structures indicate that organisms diverged at some point

- Indicates they may have developed from a common common ancestorancestor

5. Comparative embryology

- Early embryo’s are very similar in structure

Theories of Evolution

A. Lamarck – early 1800’s- Said new organs arise as they are needed1. Theory of Use and Disuse

- Organs that are used become bigger and stronger

- Those that aren’t used eventually disappear

2. Transmission of Acquired Traits

- New traits can be passed on to offspring- Causes gradual change in species

But was WRONG!!!!!

Weisman - Cut of tails of mice and then breed them

- None of the mice were born without tails

- Disproved Lamarck

Charles Darwin - 1830’s

- Said populations change due to variations and natural selection

- Variations that prove to be helpful enable those organisms to have a higher selection rate ( more offspring)

Darwin's Major ideas include:

1. Overproduction -Within a population more offspring are born than can possibly survive and reproduce

2. Competition - Organisms must compete for finite resources- food, mate, place to live

3. Survival of the Fittest - Organisms that survive are those that are best adapted to the environment- Traits that help an organism have an adaptive value

4. Reproduction- Those animals that survive are able to reproduce

5. Speciation - After many generations adaptations are perpetuated until the organisms have evolved into a form different from the original

Problem: What is the source of Darwin’s variations?Mutations - Sudden spontaneous changes in genetic

material- Mutations are rare, and mostly harmful or even lethal

- In very rare cases a mutation can have beneficial results

Normal Short wings Curly wings No eyes Legs on head

- In order to be passed on to offspring, mutations must take place in the sex cells

- If a mutation takes place in a body cell then the individual may change, but the mutation will not go to the offspring

Chromosome Mutations

Non-disjunction- Gametes have more or less chromosomes than they are supposed

-results in Down’s syndrome, marfans syndrome, others

Structural Alterations of Chromosomes

- Translocation - Transport part of a chromosome to a non-homologous chromosome

- Addition - Gain a portion of a chromosome

- Deletion - Lose a portion of a chromosome

Gene Mutations

- The adaptive valueadaptive value of the mutationmutation is dependent on the nature of the mutation and the type of environment in which the organism interacts

Mutagenic Agents - Increase the likelihood that a mutation will take place

- radiation

- chemicals

Natural Selection

1. Traits with high survival value tend to increase in frequency in a population – are passed on to offspring

- The populationpopulation not the individual changes as a result of evolution

2. If environmental conditions change then the survival value of a trait can also change

Artificial Selection

• Selective breeding - used to obtain traits that are desired by mating animals with desired traits together

Plant artificial selection

Teosinte vs. modern corn

Tomato

1. Penicillin- Less effective today because bacteria which had a mutation allowing them to survive in a penicillin environment were able to multiply – those that died did not have the survival trait

2. Insecticides

- Bugs that had a mutation allowing them to live in a pesticide are still around and reproducing

Selecting Agents

- Insecticides are not as effective anymore

*** It is important to note that the mutation was NOT caused by the antibiotic or by the insecticide. The mutation was “selectedselected” because it had a high survival value.

- Select the organisms that are going to survive

Geographic Isolation

- Changes in gene frequencies are more likely in small populations- Isolated populations may evolve into a separate species

WHY?

1. Gene frequencies may be different initially

2. Different mutations occur in main population and in isolated population3. Different environmental factors may be acting on each population

- This is what happened on the Galapagos islands with the finch

How long does it take for evolution to take place?

Two theories :

1. Gradualism - Evolution take place slowly and continuously- Supported by fossil records showing only slight

differences over thousands or millions of years

2. Punctuated Equilibrium

- Species remain stable for long periods of time with sudden bursts of rapid evolution- Also supported by fossil record

-fossils record shows little changes from layer to layer then suddenly there are lots of changes

How did life begin on Earth?

Heterotroph Hypothesis

- Assumes that Earth started as a hot body of inorganic substances in gas, liquid, and solid states and lots of energy in the environment

- Energy from the Earth caused chemical bonds to form in the “hot thin soup” of the seas

- Led to formation of organic substances

- sugars, amino acids, nucleotides

- Experiments have been done with chemicals and an environment similar to primitive earth

- Cell like structures were formed-some of these probably “ate” other molecules

- Eventually evolved with ability to reproduce - Were probably anaerobic at first

- Added CO2 to environment- Some of these evolved the ability to use CO2 and became first autotrophs

- Autotrophs added O2 to atmosphere-aerobic organisms then evolved