Darwin and Natural Selection

Before Darwin…

- People believed that species were stagnant and that Earth was only 10,000 yrs. old and also unchanging

-1700’s Georges Buffon used fossils to say the Earth was much older than a couple thousand years

-1800’s Jean Baptiste Lamarck founded the theory of evolution (he was wrong)

Charles Darwin

Designed theory of natural selection (not the theory of evolution) based on observations of nature

Expanded upon Lamarck’s evolution and disproved conventional wisdom of the time

Darwin’s 2 main points

1. Descent with modification: all species are derived from a common ancestor, but over time they have changed and adapted

2. Natural Selection: individuals with characteristics more suited to the environment reproduce more, passing on their trait

Natural Selection- 4 key concepts

Variation: Organisms (within populations) exhibit individual variation in appearance and behavior.  These variations may involve body size, hair color, facial markings, voice properties, or number of offspring.  On the other hand, some traits show little to no variation among individuals—for example, number of eyes in vertebrates. 

Inheritance.  Some traits are consistently passed on from parent to offspring.  Such traits are heritable, whereas other traits are strongly influenced by environmental conditions and show weak heritability.

High rate of population growth. Most populations have more offspring each year than local resources can support; leading to a struggle for resources. Each generation experiences substantial mortality.

Differential survival and reproduction. Individuals possessing traits well suited for the struggle for local resources will contribute more offspring to the next generation. 

How many moths?

Natural Selection- 4 key concepts

Bacteria evolve through natural selection too!

Coevolution

Coevolution Definition Coevolution is a change in the genetic

composition of one species (or group) in response to a genetic change in another.

The two species must interact with each other within the same ecological system or community

As they interact, the two species must put pressures on each other

The Two Species Must Interact With Each Other There are several ways different species interact

Two plant species may be vying for soil, sunlight or water

Two animal species may be vying for the same food source, territory or one might be the predator to the other

An animal species may be feeding on a particular plant species

A parasite species may favor a particular plant or animal species

As They Interact, the Two Species Must Put Pressures on Each Other What is the difference between biotic and

abiotic evolution?Biotic pressures include predation or competition

for resources (possibility of coevolution)Abiotic pressures are non-living environmental

features such as snow, extreme temperature changes and chemical pollution (possible simple adaptation)

Simple Adaptation The snowshoe hare

changes its coat twice per year to be less conspicuous to predators such as the bobcat

The bobcat hasn’t adapted any particular change in vision to overcome this adaptation in the hare

Coevolution Some populations of the

newt have developed tetrodotoxin in their skin for use as a defense

The garter snake preys on the newt in each community they are found together

Some communities have no toxin while others have what seems to be overkill

WHY?

Microevolution Evolution on a small scale A change in gene frequency in one

specific population

If you could zoom in on one branch of the tree of life, you could continue zooming in until you saw the relationships between specific populations.

But how do you know when you’ve reached the population scale?

Population: A group of organisms that interbreed with each other.This could mean a group of animals on an

island, a pair of animals that will mate, or anything in between.

Artificial Selection a process in which humans purposefully

select organisms for reproduction to either keep or lose traits.

Mutation a change in a DNA sequence, usually

occurring because of errors in replication or repair.

Mutation is the ultimate source of all genetic variation.

Gene flow the movement of genes between

populations. This may happen through the immigration and emigration of organisms

Natural selection

A process in which some individuals have genetically-based traits that improve survival or reproduction and thus have more offspring surviving to reproductive age than other individuals.

Genetic drift

random changes in the gene frequencies of a population from generation to generation. This happens as a result of sampling error—some genotypes just happen to reproduce more than other genotypes.

This process causes gene frequencies in a population to drift around over time.

What is a species? A population or group of populations that

can breed with each other and produce fertile offspring

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Fossils

How are fossils made?

Fossil making in action

http://www.flmnh.ufl.edu/fhc/layer2.htm

Fossils can come from either body parts or traces like nests, footprints, burrows, etc.

4 Types of Fossils 1.Mold fossils--

2.Cast fossils-- 3.Trace fossils-- 4.True form fossils-

Mold fossils A mold of the organism is made in a

substrate (some sort of lasting material)

Cast Fossils

When a mold fossil is filled in

Trace Fossils

Fossils made by signs that the animal existed instead of its actual body parts

True form fossils

Fossils made of the

actual animal or

animal part

How are fossils made? Trapped in amber (hardened sap) Coalification- carbon is the only element left Replacement- hard parts dissolve, replaced by

minerals like iron, calcite, silica Petrification- minerals form rock like fossil Molds Recrystalization

How do we know how old a fossil is?

How deep is it buried Relative dating Radioisotope dating

Carbon 14Uranium 235

Stratigraphy

Dating fossils based on where they lie in sediment

Relative Dating

Radioisotope dating

An estimate of a rock's age can be determined by examining the ratios of the remaining radioactive element and its daughters.

For example, when lava cools, it has no lead content but it does contain some radioactive Uranium (U-235).

Radioisotope dating

Over time, the unstable radioactive Uranium decays into its daughter, Lead-207, at a constant, known rate (its half-life).

By comparing the relative proportion of Uranium-235 and Lead-207, the age of the igneous rock can be determined. Carbon-14 (which decays to Nitrogen-14) is also used to date fossils.

Example

The half life of Carbon-14 is about 6000 years.

If a fossil contained 50% of the original carbon-14, how old is the fossil?

If a fossil contained 75% of the original carbon-14, how old is the fossil?