Evolution and Natural Selection

Why are we so different, yet so alike?

This class will be discussing the HOW we evolved, not the WHY

• How we evolved→ realm of science

• What is our purpose in life→ realm of religion / philosophy

Evolution does not disprove the existence of a deity / deities

Evolution is the mechanism for the variety of living organisms on Earth.

Yet, this mechanism does not refute religious/spiritual beliefs on the purpose of life.

Origin of our Universe – The Big Bang

• Proposed in 1927 by George Lemaitre

Concept: The universe started between 10-20 billion years ago from an initial explosion.

• All of the universe’s material was contained in the singularity,

• After this explosion, the material in the singularity has expanded outwards, and has since been expanding

Source: Earth: Portrait of a Planet, 2nd Edition

Origin of our Universe – The Big Bang

• Seconds after the explosion, the first atoms started to form (hydrogen and helium)

• Clouds of hydrogen and helium formed, eventually collapsing on itself making starts and galaxies • Think of each atom as a mini planet… therefore each atom’s gravitational pull

caused them to “collide” and eventually form a large mass.

Origin of our Solar System – Nebular hypothesis

• The first to form was our Sun, approximately 4.65 billion years ago • A nebular cloud of gas and dust, which was formed due to gravity pulling and

the material collapsing on itself

• This “ball” became hot enough for it to self-ignite (fusion), giving birth to a star…the Sun!

Horse Head Nebula Location: In the constellation Orion Source: Nasa

Map of the Constellation Orion with the stars labelled

Origin of our Solar System – Nebular hypothesis

• Disks of “dust” revolved at different distances around the Sun • “Dust disks” formed into the planets

• The distance you are from the sun → determines the type of planet you are!

Origin of Life on Earth

• Before “life” could have evolved, the Earth needed to have all the conditions for life to feasibly take place: • Develop an atmosphere

• Earth to cool down

• Water vapour to condense (chemical reactions need liquid water)

• Formation of continents (synthesis of molecules also requires a solid surface to bring substances and water together)

Origin of Life on Earth

All living things are composed of complex molecules

• Complex molecules need to synthesize from simple molecules

• Newly complex molecules need to bond to form cells

• These cells need to replicate into other cells

For this to happen, you need:

• Source of energy (the sun, check!)

• Liquid water (condensed water, check!)

• Lots….and lots….and lots….and lots of time

1st living thing on Earth

Single cell bacteria

• From there, it just evolved, and evolved, and evolved, and evolved!

1st living thing on Earth

• This single cell bacterial had all the “necessities” to be called “living” 1. Made of at least one cell

2. Uses energy to function

3. Respond to its environment

4. Grow/repair

5. Reproduce

DNA → Living things’ “Instruction Manuel”

• All living things need to encode their information in a way that can: 1. Used by the organism to grow and repair itself

2. Passed down to the offspring

• This is done by DNA

Source: ASHG

DNA → Living things’ “Instruction Manuel”

• It is found in the nucleus of cells

• It is a two stranded helix with four base pairs 1. Adenine

2. Guanine

3. Cytosine

4. Thymine

DNA

Computer rendition of DNA strand

DNA

DNA → Living things’ “Instruction Manuel”

• The arrangement of base pairs form genes

• A gene is a segment of DNA that has specific information to make molecules which make organisms

DNA Analogy: Instruction Books

DNA Analogy: Instruction Books

DNA → Language which instructions are written in

Bases → Letters in the language

Combination of bases → Words

Gene → A combination of words creating sentence of instructions

Chromosome → Chapters in your instruction book

Genome → The complete book

Copying cells → Mitosis

• For DNA to be passed on, it must be copied

• Simple organisms (bacteria) practice asexual reproduction; meaning it reproduces by itself

• Mitosis is a form of cell division where the parent cell is identical to the daughter cell • This is the way the cells in our body grow and repair

Mitosis The parent cell copies itself, forming two identical daughter cells

Parent Cell

Daughter Cell #1 Daughter Cell #2

Copying cells → Mitosis

• Downfall for reproducing by asexual reproduction → little genetic diversity

Creating Genetic Diversity → Meiosis

• More complex organisms (humans) practice sexual reproduction; meaning it requires genetic information from two individuals to reproduce

• This creates new genetic variations in the species

Creating Genetic Diversity → Meiosis

• For sexual reproduction to take place, special cells called gametes need to be formed • Sperm in males

• Ova in females

• These cells have half of the genetic information of the parent cell

• When the sperm and ova meet, they will combine to have a full set of genetic information that is distinct from the parents

Meiosis The parent cell copies itself, forming four genetically different daughter cells with half the genetic information of an organism

Parent Cell

D. C. #1 D. C. #2 D. C. #3 D. C. #4

Meiosis → Mechanism to Mutation

• Species evolve due to the occurrence of mutation in the genetic code • This provides the “raw material” for new species to evolve

• Mutation: a permanent change in the DNA sequence of an organism

Mutation → Leads to speciation….but!

• Just because you have a mutation in your sequence doesn’t mean you will be a new species overnight • You have lots and lots and lots and lots of genes in your body that code for

lots and lots of traits

• Mutations can cause slight changes in a particular gene • Leading to variations

• Mutations can cause a gene to not work

• Mutations can cause a gene to completely change

And this needs to take place over a long, long, long time!

Sickle Cell Anemia: Mutation causing slight change in a gene

Albinism: Mutation causing a gene not to work

Connie Chiu; Fashion Model Albino Kangaroo

Albinism Melanism

Mutation’s fine, but you need to “Select” it

• A mutation in the population will only stay in the population if it is selected for it

• The mutation needs to give the organism an “edge”, so that it can survive in its habitat more than organisms that don’t have the mutation

Mutation’s fine, but you need to “Select” it

• It’s only when you have selected the mutation, does it stay in the population

• It’s rounds of mutation and selections that lead to new species forming

• Which, of course, takes lots and lots and lots of time!

Natural Selection is the logical result of four features of living systems: 1. Variation: Individuals in a population

vary from one another 2. Inheritance: Parents pass on their traits

to their offspring genetically 3. Selection: Some variants reproduce

more than others 4. Time: Successful variations accumulate

over many generations

Peppered Moth Story → “Modern Day” Natural Selection

The man who proposed The Theory of Natural Selection → Mr Charles Darwin

Evidence that Evolution has taken place? Fossils! • Fossils are remnants of species that existed

• We can figure out how old fossils are by how old the rock they are in is

• Mostly all fossils are in sedimentary rock (rock formed by sediment, like sand and dirt, layering on top of each other)

Evidence that Evolution has taken place? Fossils! • Key in the fossil record is the law of superposition

• In any undisturbed rock sequence, the youngest rock layer is on top and the oldest rock layer is on the bottom

• That means we can figure out how old fossils are based on the layer of rock they are in (This give us the relative date)

• We can figure out for “absolute” certainty how old a fossil is by carbon dating

HAVE A WONDERFUL SUMMER!!

Don’t forget, you have your lab exam next class!

Don’t also forget, your science exam is June 8th!

Study hard!