Biological Evolution: “Change in the genetic composition of

a population during successive generations (due partly to natural selection) and resulting in the development of new species” (Webster’s).

The ancestors of the horse, for example, have undergone considerable change in physical size and proportions over the last 60 million years.

The adult size, shape, bones, internal organs and many other physical and behavioral features have changed.

The original Eohippus was thus a different “type of animal” (species) than the present day horse (Equus)

Such changes in body parts are the result of changes in genes. When nature “selects” the “fittest” for survival and reproduction, it is also selecting the fittest combination of genes to survive and reproduce. These come “packaged” in a creature’s body.

Biological Evolution happens through transmission of genetic characteristics from one generation to the next

Individuals who are the most genetically “fit”, survive to reproduce (called natural selection or “survival of the fittest”) and pass on their fit characteristics

“Natural selection” is a metaphor which Darwin compared to “artificial selection” (the breeding of plants & animals).

Artificial selection = humans “select” which individual plant or animal will reproduce.

Natural selection = nature does this “selecting”.

Varieties of bananas produced by artificial selection

Note how all these dramatically different vegetables were created by artificial selection from an original ancestor.

How does Natural Selection work?

Four main Principles of Natural Selection• 1. Variation

tendency for individuals in a species to differ slightly from their parents and from each other (genetic recombination/mutations).

• 2. Overproduction While having many offspring raises the chance that some will survive, not all will

survive due to competition for resources.

• 3. Adaptation Certain variation allows an individual to survive better than other individuals it

competes against. More successful individuals are “naturally selected” to live longer and produce more offspring that share those adaptations for their environment.

• 4. Descent with Modification Over time, natural selection will result in species with adaptations that help it

survive and reproduce. More individuals will have the trait in subsequent generations, as long as the environmental conditions remain the same.

Important Note:Adaptations do not give an

individual or species what they “need” to survive.

The “best” or most “fit” features are “naturally selected”

An adaptation is a structure, behavior or physiological process

Help an organism to survive and

reproduce in particular environment

Adaptations are inherited from their parents

It also refers to the ability of living things to adjust to different conditions within their environments. 

Structural adaptation involves some part of an organism's body.Teeth Body coverings

ShellsQuillsScales  

CamouflageMimicry

Camouflage allows an animal to blend into its environment. 

Makes it hard for enemies to single out individuals  

Mimicry allows one animal to look, sound, or act like another animal to fool predators into thinking it is poisonous or dangerous.  

Vascular-stems Root systems Thorns Leave type

Broad:absorb more sunlight

Small needle-like: reduce water loss

Waxy: reduce water loss, protect from fire

Poisonous/toxins

Behavior adaptations include activities or behaviors that help an animal survive. 

1. Innate 2. Learned 3. Survival 4. Seasonal

INNATE

Inherited through the genes

Examples Flying for bees, birds Swimming for fish Walking for humans Speaking for humans

LEARNED

Learned from experience or from observing other animals

Examples Type of language spoken

for humans Riding a bicycle

1. Finding food Predator-Prey adaptations

Predator-animals that eat other animalsPrey-animal being eaten

2. Marking Territory Way that animals inform other animals that an area is

occupied3. Defensive Action

Protect resources, themselves, food, mates, offspring4. Courtship

Behaviors used to find a mate5. Parenting

Depend on parents for survival

Some animals use these methods of defense to protect themselves: Camouflage

Snake Mimicry

Mexican Milk Snake Bright colors

Skunk and Poison Arrow Frog

“Hair” projectionsHedgehog quillsDeer Antlers

Help organisms adapt to the environment

1.Migration2.Hibernation3.Estivation4.Biological Clock

Behaviors controlled by the brainReflexesBlinkingPainSwallowingTolerance to a certain poisonLogical thinking

Warm-blooded All have some type

of “hair” Some are very

specialized, such as white polar bear fur

Care for young

Leg Length Roseate Spoonbill

(top right) Foot Webbing

Laughing Gull (top left)

Beak Shape Long Billed Curlew

(bottom)

cold- blooded Scales Some undergo

hibernation and estivation

Lay eggs on land Leg structure and

position

Cold-blooded Lay eggs in water Partially of fully

webbed feet Have lungs or can

absorb oxygen through their skin

Depends on reproductive successOperates on a population, NOT on an

individualDynamic between genetic change and

the changing environmentEnvironment exerts selective pressure:

environmental conditions that select for certain individuals and select against others

Natural Selection can take time or can happen quickly

Fossils• Allow us to visually see organisms change over

time Geography

• Being able to see the distribution of organisms around the world

Embryology• Similar features of embryos in very different

organisms suggest evolution from a distant common ancestor

Anatomy• Homologous structures – features that are similar in

structure but appear in different species offers strong evidence for common descent.

Vestigial structures• Underdeveloped or unused features are remnants of

organs or structures that had a function in an early ancestor. Snakes have tiny pelvic bones that are homologous to lizards but are not needed. Ostrich has wings that have little or no use now.