1. Evolution Unit Summary Note

2. Theorists
Aristotle: Greek philosopher who arranged all life into a ladder (Scala Naturae)
Buffon: believed species change over time and some animals have common ancestors. (one canine gives rise to all canine species)
Lamarck: inheritance of acquired traits. A giraffe can gr a long neck by reaching, and then pass that long neck on to offspring.
Darwin and Wallace: Natural selection. Organisms with the traits best suited to the environment live to pass on genes.

3. Natural Selection
Overproduction: organisms make more babies/sperm/eggs/pollen than expected to survive
Variation: there are differences between organisms (within the same species, and between species)
Competition: organisms fight for limited resources (food, mates, shelter, territory, escaping predators)
Survival of the fittest: those with favourable traits live to pass on genes for those traits.

4. Why populations change over time
Mutations: Each time cells are copied there is a chance there will be a mistake in the DNA. Since DNA controls the traits of an organism, this means babies could be born with random different traits.
Sex: Each time the genetics of two different individuals is mixed together the offspring produced will have a different combination of traits than the parents.
Genetic drift: genes are sorted randomly during the production of sperm and eggs, this means there is a lot of random chance involved in which traits offspring will have. Over time a population can have a specific trait become common just due to random luck.
Migration: individuals leave populations and join new populations. They bring their genes with them, and when they breed in the new population they change its gene pool
Selecting agents/pressures: the environment around a population is always changing. Any factor that causes some to live and breed while others don’t affects the distribution of traits in the future population.

5. Why new species evolve (Speciation)
A common model for a new species evolving is when a group of animals moves away from the main population to a new environment and then over time changes from the original population. Main parts of this model are:
Geographic isolation: a group separated from the main population by some barrier (mountain range, ocean, etc) in a new environment with different selecting pressures in it.
Reproductive isolation: After millions of years in the new environment, the group that got separated is now so different it can’t breed with the original population anymore.
Speciation: the group is now considered a different species from the original population. A species is a collection of organisms that can breed with each other and produce viable offspring.

6. Evidence for Evolution
Fossils: old bones found, show that there were once organisms that are now extinct. Also, age and features of different fossils show progression of evolution (only direct evidence, rest is indirect) Fun fact: fossils found at deeper levels in the earth’s crust are older than those found higher up.
Embryos: all animals have embryos that go through similar stages of development. Show that all life on earth is related.
Vestigial structures: organs animals have that don’t have a use imply the animal evolved from something where the organ used to be useful.
Physiological and biochemical evidence: similarities in hormones and DNA between species show life on earth is related.

7. Evidence for Evolution continued
Anatomy: different species of organisms with similar structures show life on earth is related.
Homologous structures: have a similar structure but different use (EX: human arm and bat wing, similar bone structure, one grabs and climbs, the other flies) This shows the two animals had a common ancestor that went through divergent evolution.
Analogous structures: have different structures, but they are used for the same thing. (Ex: bat wing and bird wing, both for flying, one made of one and skin, other made of feathers) This shows animals will evolve to fill the same ecological niche (called convergent evolution)

8. Human interference
Artificial Selection: humans can breed animals together to try and get offspring with desirable traits. This mimics the mechanism of natural selection, but the selecting pressure/agent is what people’s choices.
Ex: different dog breeds are the result of artificial selection
Accidental selection: when trying to do one thing, humans sometimes accidentally affect a population of organisms, changing the distribution of traits.
Ex: a factory pollutes an area and changes the colour of local tree bark from white to black. White moths now stand out and are eaten, population of moths goes from half white half dark to mostly dark.

9. Hybrids
When two species are similar enough they can breed and have babies, BUT those babies are sterile because their genes don’t quite match properly, we call the babies hybrids
Most hybrids are created because of human interference. Some happen randomly in the wild but it is rare.
Examples humans create on purpose: tiger + lion = liger horse + donkey = mule grape species 1 + grape species 2 = seedless grape
Examples that have happened in nature: grizzly bear + polar bear = pizzly bear coyote + wolf = coywolf

10. Extinction When an entire species dies out it is considered extinct.
There have been major cataclysmic extinctions in the past where many species were wiped out, such as when the dinosaurs died or when ice ages occur.
(Why did dino’s die? We are not sure. May have been a giant asteroid, or a change in climate, or a rapid evolution in the plant life, or they were outcompeted by mammals and birds or wiped out by viruses.)
There are more and more organisms being driven extinct now because of us humans (killing them, destroying or polluting their habitat, killing their food sources, taking over their territories)