Biology - Evolution

Half Life

amount of time it takes for a particular isotope to decay to half its original amount

Early Earth conditions

The Earth was formed about 4.6 billion years ago.

• The surface was extremely hot, with volcanoes, lava, and no oxygen in the atmosphere.

• There were toxic gases, frequent storms, and no life at first.

• Over time, Earth cooled, water formed oceans, and simple life began to appear.

Geologic time

A timeline of Earth’s history that covers billions of years.

• Divided into eras, periods, and epochs.

• Helps scientists understand when major events (like extinctions and evolution of species) happened.

Extinction

happens when the last individual of a species dies, and it can no longer reproduce or survive.

Earliest life

believed to be simple, single-celled organisms like bacteria.

• Appeared about 3.5 to 4 billion years ago.

Precambrian time

The longest part of Earth's history, lasting from the formation of Earth (about 4.6 billion years ago) to around 541 million years ago.

• Most of Earth's early development happened during this time.

• The earliest life appeared in this time.

Relative dating

A method to determine the age of rocks or fossils by comparing them to other layers.

• Does not give exact age, just shows which layers are older or younger.

• Based on the Law of Superposition (lower layers are older).

Radiometric dating

A method to find the exact age of rocks or fossils using the decay of radioactive elements.

• Uses the concept of half-life to measure how long a substance has been breaking down.

Charles Darwin

A British naturalist who developed the theory of evolution by natural selection.

• Traveled on the HMS Beagle and studied species, especially on the Galápagos Islands.

Origin of Species

A book written by Charles Darwin in 1859.

•  Full title: On the Origin of Species by Means of Natural Selection.

• Introduced the idea that species change over time and new species form through natural selection.

Natural Selection

 the process by which organisms with variations most suited to their local environment survive and leave more offspring

Artificial Selection

breeding of organisms (by people) to produce offspring with desired traits.

• Traits purposely selected

• Process is controlled with a specific intent in mind

Evolution

gradual change in a species through adaptations over time

Adaptation

any variation that aids in an organism's chance for survival

Antibiotic Resistance

Antibiotic resistance happens when bacteria change and become able to survive antibiotics that used to kill them.

• This means the medicine no longer works to treat infections caused by those bacteria.

Homologous Structures

structural features with a common evolutionary origin

Analogous Structures

structures with different evolutionary origin but similar structure and function

Vestigial Structures

left over structures in present day organisms that had a use for that organism’s ancestors

Allelic Frequency

the percentage that a specific allele makes up in a population

Genetic Equilibrium

when the allelic frequencies in a gene pool remain constant

Gene pool

the total of all the alleles in a population of organisms

Stabilizing Selection

takes place when individuals near the center of the curve have higher fitness  than individuals at either end

Disruptive Selection

occurs when individuals at the outer ends of the curve have higher fitness than individuals near the middle of the curve

Speciation

the formation of new species

Directional Selection

occurs when individuals at one end of the curve have higher fitness than individuals in the middle or at the other end

Geographic Isolation

occurs when two populations are separated by geographic barriers such as rivers, mountains, or bodies of water

Behavioral Isolation

when two species do not mate because they have different behaviors, such as mating calls, courtship dances, or other rituals.

• Even if they live in the same area, they don’t recognize each other as mates.

Temporal Isolation

happens when two or more species reproduce at different times

Reproductive Isolation

Two populations in a species become increasingly distinct and can no longer interbreed

 How many half lives would it take for a radioactive isotope to be reduced to ⅛ of its original amount?

It takes 3 half-lives.

After 1: ½, after 2: ¼, after 3: ⅛.

Describe three major insights that Darwin had in his voyage aboard the HMS Beagle that contributed to the Theory of Evolution by Natural Selection.

• Species vary globally – animals in different parts of the world are different but similar.

• Species vary locally – different environments have different versions of similar animals.

• Fossils resemble living species – extinct animals looked like animals still alive today.

Briefly describe the ideas of three contemporaries of Darwin who influenced his thinking.

• Charles Lyell (geologist): Believed Earth changed slowly over long periods. This helped Darwin realize life might change slowly too.

• Thomas Malthus (economist): Noted that populations grow faster than resources, causing competition. This helped Darwin think about "struggle for survival."

• Jean-Baptiste Lamarck (biologist): Suggested species could change over time and pass on traits, even though his mechanism (use and disuse) was incorrect.

Differentiate between species change over time as proposed by Lamarck and as described by Darwin.

• Lamarck: Traits gained during life can be passed on (e.g., giraffes stretch necks).

• Darwin: Natural selection chooses traits that help survival; changes happen over generations.

What is the difference between natural selection and artificial selection?

• Natural selection: Nature selects traits best for survival.

• Artificial selection: Humans choose traits to breed (e.g., dogs, crops).

Can individual organisms evolve? Why or why not? What can evolve?

• No, individuals cannot evolve.

• Evolution happens in a population, not a single organism.

• Evolution is a change in the gene pool (allele frequencies) over time.

• Individuals may adapt, but only populations evolve across generations.

What are some of the general types of evidence for evolution?

• Fossils – Show how organisms changed over time.

• Comparative anatomy – Similar body structures (like arms) show common ancestry.

• DNA and genetics – Similar DNA shows relatedness between species.

• Embryology – Early embryos of animals look very similar.

• Direct observation – We can see evolution happening today, like bacteria becoming antibiotic-resistant.

Give an example of evolution that can be observed in a short amount of time.

• Antibiotic resistance in bacteria – Some bacteria survive medicine, reproduce, and pass on resistance.

• Peppered moths – Changed color during the Industrial Revolution to better match their environment (from light to dark).

Compare and contrast homologous, analogous, and vestigial structures.

• Homologous structures: Same origin, different function (e.g., human arm, whale flipper, bat wing – same bones, different uses).

• Analogous structures: Different origin, same function (e.g., bird wing vs. insect wing – both for flying, but built differently).

• Vestigial structures: Useless or reduced parts that had a function in ancestors (e.g., human appendix, leg bones in whales).

What are three ways that natural selection can proceed with polygenic traits? How do they differ from each other?

• Directional selection: One extreme trait is favored (e.g., longer beaks in birds help get food).

• Stabilizing selection: The average trait is favored, extremes are selected against (e.g., medium-sized babies are more likely to survive than very small or large ones).

• Disruptive selection: Both extremes are favored, average is not (e.g., birds with very small or large beaks survive better than those with medium ones).

Give two examples of speciation, the formation of a new species. List what “isolation” term applies to each example.

• Darwin’s finches (Galápagos Islands) – Geographic isolation: separated by islands, evolved into different species.

• Different frog species with different mating calls – Behavioral isolation: don't recognize each other as mates.

• (Other possible isolation types: temporal isolation – mating at different times, reproductive isolation – incompatible reproductive parts.)

What is genetic equilibrium? What is not happening in a species that is in genetic equilibrium? Explain briefly.

• Genetic equilibrium is when the allele frequencies in a population do not change over time.

• Means no evolution is occurring.

• To stay in equilibrium, there must be:

  • No mutation

  • No natural selection

  • No gene flow (immigration/emigration)

  • Large population size

  • Random mating

Describe the evolutionary relationship between humans and chimpanzees

• Humans and chimpanzees share a recent common ancestor.

• Our DNA is about 98–99% similar.

• They are not descended from each other, but from a shared ancestor that lived around 6–7 million years ago.

• Over time, each species evolved in different ways.