Evolution – A scientific theory that states that living species are descendants of ancestral species that were different from present day ones (the genetic changes in a population over generations)

Scientific Theory – a well-supported explanation for some aspect of the natural world that includes many observations, inferences, and tested hypotheses (it is not “just an opinion or belief”)◦ Main difference between scientific law and

theory is that a law says that something does occur while a theory attempts to explain why it occurs.

Evolution

Like Darwin, Also believe populations change over time

BUT, his beliefs are no longer supported Lamarck’s ideas on evolution:

1. Believed in Spontaneous Generation2. Simple forms of life eventually develop into more complex

forms3. Traits gained in life by experience or behavior could be passed

on to offspring

(Ex. Bodybuilder parents Bodybuilder baby)

Jean Baptiste Lamarck (1744-1829)

Darwin was 22 years old when he sailed from Great Britain on the H.M.S. Beagle.

He spent the voyage collecting thousands of specimens of the fauna and flora, observing various adaptations of organisms. He was particularly struck by the uniqueness of the fauna of the Galapagos Islands.

Eventually he released the book “On the origin of Species by Natural Selection”. ◦ (He was not the first or only person to believe that life

changes over time, but he was the first to come up with the correct method by which evolution occurs.)

About Darwin

(1) Descent with Modification Basically, the process of evolution Living species descended with changes

(modifications) from prior species Species must be able to change over time Ex. Darwin’s Finches

(will discuss later)

Charles Darwin’s Ideas

(2) Natural Selection “Survival of the fittest” The process by which organisms best suited

to the environment survive, reproduce, and pass their genes to the next generation.

Fitness -(1) Survive Longer, (2) Reproduce More (3) Pass on traits to next generation

Occurs in populations, not in individuals◦ Note: It is not essential to survive longer. The

longer life simply gives more time to produce more offspring. Ex. Evolution would favor someone who was 20 and had 4 kids rather than someone who is 80 with 1 kid.

Charles Darwin’s Ideas

How does evolution occur through natural selection?

1. Organisms produce more offspring than can survive.

2. Genetic Variation - Individual organisms in a population have slight variations or adaptations.

3. Individuals struggle to survive, those with adaptations best suited to the environment are more likely to survive.

4. Survivors pass on genes for the adaptations to their offspring.

5. Gradually, the population’s gene pool changes and the population evolves.

Example of Darwin’s Observations of Natural Selection - Darwin’s Finches

13 different species of finches on the Galapagos Islands

Each species has a beak that is best adapted for a certain kind of food that is found on the different islands

Another Example of Natural Selection Beetles living on brown tree bark are either

brown or green. Predator (bird) can more easily see green

beetles and will catch them more often than brown.

Brown beetles live longer and produce more offspring, to whom they pass the gene for brown.

Natural selection is an “editing” process, not a creating one

If the environment changes and there is not a suitable phenotype to survive in the new environment then the species will go extinct.

There is no amount of “trying” that can help you evolve.

Nature simply “selects” the greatest physical traits to survive in different environments and those are passed on.

Note

The next few slides are all species observed by Darwin on the Galapagos Islands that led to him create his theories of descent with modification and natural selection.

Blue Footed Booby

Video

Marine iguana

Video

Swallowtail Gull

Finch

Hawkfish

Lamarck vs Darwin’s Ideas About Evolution

Eventually get a new species

Eventually get a new species

Lamarck “Acquire” new traits

though use or disuse “Acquired” traits are

passed on to offspring Evironment creates a

need for certain “acquired” traits

Darwin Inheritable traits

already exist Organisms with “new”

and “different” trait can pass it on to offspring

Certain traits are “selected” by nature because the organism is better able to survive

1) Directional Selection Selection that favors one extreme

phenotype (physical type) This causes this particular extreme

phenotype to become much more common (the look of the population is pushed in 1 direction)

Ex. Peppered Moths

3 Types of Natural Selection

Directional Selection

2) Disruptive Selection Selection that favors both extreme

phenotypes (physical type) This causes extreme phenotypes to become

much more common (the look of the population shows extreme differences)

Ex. Darwin’s Finches

3 Types of Natural Selection

Disruptive Selection

3) Stabilizing Selection Selection against the extreme phenotypes

(physical type) This causes average phenotype to become

much more common (the look of the population is very similar and average)

Ex. Human weight at birth

3 Types of Natural Selection

Stabilizing Selection

Artificial selection – Natural selection that “isn’t natural”◦ Several species have evolved in certain ways due

to the influence of humans.◦ Ex. Dog breeding, Crops

**Not on Note Handout (Add to the side)

Causes of evolution? 1) MUTATIONS!!

Meiosis (and sexual reproduction) gives us variation in a population that creates a range of phenotypes that can be acted upon by natural selection.

Mutations can give rise to completely new characteristics.

MUTATION: a change in a gene◦ Remember that a gene is enough DNA to control 1 trait

On the rare occasion when mutations produce favorable traits, a population’s gene pool (all of the genes in a population) is changed because of the introduction of this new, favored trait. The population will then evolve through natural selection to show a greater percentage of the new, beneficial trait.

 

Causes of evolution - 2 types of Mutations Two Types of Mutations:(1) Changes in genes in somatic (body) cells:

can affect the organism itself, but cannot be passed to sexually produced offspring.

(2) Changes in genes in gametes (egg and sperm): do not affect the parent organism itself, can be passed to sexually produced offspring

Mutations Cont. Mutations may result in a trait that improves an

organism’s chances for survival, so that organism would be more likely to reproduce. Then the favorable mutation would be passed on to offspring.

This results in evolution. Mutations occur very rarely (and are almost always

bad), so populations evolve slowly. NOTE: EVEN THOUGH EVOLUTION GENERALLY

OCCURS SLOWLY…IT SOMETIMES CAN OCCUR RAPIDLY IF THE NEW MUTATED TRAIT IS STRONGLY FAVORED OVER ALLOTHER PHENOTYPES PRESENT IN THE POPULATION

2) Genetic Drift – changes in gene pool due to chance (has greater effect on smaller populations)

Examples◦ 1) Bottleneck effect – drastic decrease in

population size may leave only certain alleles available. These alleles will quickly be perpetuated.

◦ 2) Founder effect –When a few individuals colonize a new area (same reasoning as bottleneck)

Causes of Evolution

Bottleneck Effect

3) Gene flow Introduction or exit of alleles in a population

whenever individuals enter or leave.

Causes of Evolution

Notice that all 3 causes for evolution (mutations, genetic drift, and gene flow) all have 1 similarity – they change the GENE POOL of the population.

Note on causes of Evolution

1) Molecular Biology All living things use DNA and RNA. The genetic code amongst all living things is

universally the same. (In other words, the fact that the RNA codon AUG gives the amino acid MET in humans is seen in every other living thing as well)

This fact more than any other (at least to me) indicates that all living things originated from a common ancestor.

Evidence for Evolution

Molecular Biology – Continued The closer 2 different species DNA is to one

another, then the closer those 2 are related. Which 2 species are closer related?

Species A: AACTGGCTTA Species B: AACTAACCCG Species C: TACTGGCTTA

Evidence for Evolution

The remains or traces of organisms that have once lived on Earth.

Fossil Record: the history of life on Earth, based on fossils that have been discovered

The fossil record shows how organisms have changed over time and shows that the Earth is about 3.5 billion years old.

Evidence for Evolution -Fossils

Extinctions occur when there are major changes in the environment and species do not have the adaptations to survive.

The fossil record helps scientists to discover relationships between different groups of organisms and determine common ancestors.

Evidence for Evolution - Fossils

The Earth is divided into layers called strata.

Generally speaking, the lower the strata = the older the layer of Earth (each new layer becomes stacked on the older layer below it)

This means if two fossils are found, the fossil found in the lowest layer would be the oldest

There are also techniques for determining the absolute (or relatively exact date) of a fossil’s age

Determining the age of fossils

Evidence for Evolution – Comparative Anatomy

Convergent evolution – process by which different species evolve similar traits

(SAME FUNCTION, DIFFERENT ANCESTOR)

Example: Birds, bats, and moths have wings, but they did not evolve from a recent common ancestor.

Caused by:◦ living in similar habits /

performing similar functions

Structures with closely related function but do not come from the same ancestral structure◦ Same function, different structure

Example: Birds, bats, and moths have wings, but they did not evolve from each other.

Analagous Structures (derived from Convergent evolution)

Divergent evolution- build up of differences between groups which can lead to the development of a new species

In other words, two different species that evolved from the same ancestor.

Caused by populations of the same species:1. moving to two different environments or..2. specializing in different areas of the same

environment

Evidence for Evolution – Comparative Anatomy

Structures in different species that originated from common ancestor

May have different function but similar structure

Homologous Structures (derived from divergent evolution)

Evidence for Evolution –

Vestigial structures – no longer have a use, but may have had a use in evolutionary

history.

Ex: human tail bone (coccyx) made of 4 fused vertebrae that resemble the bones in an animal’s tail.

Other examples: the appendix, and ear muscles!

When two or more species have evolved together, the situation is called coevolution.

Example:◦ Insects and Flowers

Flowers provide food for insects. Insects take pollen from one flower to the next so they can reproduce.

Coevolution

Behavioral evolution -a behavior that is selected for strongly enough that all organisms in a species exhibit this behavior because of the survival or reproductive advantages that behaviors gives

Examples: The dancing of the blue footed booby may have seemed

peculiar to you, but the execution of this courtship ritual determines whether or not they will reproduce.

Migration is another example of a behavioral adaptation that would be essential in the survival and ability to reproduce (if you don’t migrate, you die) of a species.

Behavioral Evolution

Sexual selection-form of natural selection in which individuals with certain characteristics are more likely than other individuals to obtain mates (leads to sexual dimorphism – differences in males and females)

Physical Examples:Feathers of a male peacockAntlers of a male deerHumans

Behavioral Examples: Darwin Beetles Darwin Beetle VideoBlue footed Booby Humans

Sexual selection