Darwin and Evolution

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Evolutionary theory originated from the work of Charles Darwin in the 19th century. Darwin's groundbreaking book, "On the Origin of Species," published in 1859, introduced the concept of natural selection as the mechanism behind evolution.

Darwin observed variation in species and proposed that individuals with advantageous traits for their environment were more likely to survive and reproduce, passing on these beneficial traits to their offspring. This process, known as natural selection, gradually leads to the adaptation of species to their environments over successive generations.

Guiding Question: How did the giraffe get its long neck?

History of Evolutionary Thought

- Darwin made observations on his voyage around the world, on the HMS Beagle
- He visited the Galapagos island and observed extraordinary animals (tortoises, finches, iguanas)
- He noted some animals were found on islands that were not found on the mainland (biogeography)
- His observations lead to the Theory of Evolution by Natural Selection
- Note: evolution was not a new idea, but it was Darwin that proposed the mechanism for how it worked

Darwin's Theory of Evolution by Natural Selection

- Finches on the islands had different sized beaks
- The beaks were specialized for the type of food the birds ate
- Darwin proposed that each finch had descended from a single mainland species of finch
- This idea came to be known as COMMON DESCENT

- Another scientist, Alfred Wallace, made similar observations about islands in another region

finches finch photo

Darwin's illustration of the finches. Large beaks were adapated for cracking seeds. Smaller beaks were adapted for smaller seeds or insects.

Evolution by Natural Selection

Use VIDA to remember the process

V = variations exist in populations
I = Inheritance of traits
D = Differential survival and reproduction
A = Adapation, individuals with favorable traits survive and reproduce

Descent with Modification

Each generation will have more of the favorable traits than previous generation

A modern species can be traced to a common ancestor

Data Analysis

finch data

See Video: Galapagos Finch Evolution by HHMI

What do you see? * the average size of the beak increased after the drought

What does it mean? * the population changed

How could you explain the data? * finches with larger beaks surved and reproduced

Giraffe Evolution

- the ancestors of giraffes resble the okapi
- fossil record shows a change in the vertebrae shape (but not the number)
- individuals with longer necks survived and reproduced (natural selection)

Taxonomy - science of classifying organisms

Binomial nomenclature - a two name system, genus + species

Giraffes have several subspecies, found in different regions of Africa

Biogeography - the study of the distribution of species

Cladograms - show how the giraffes are related

Giraffes are descended from a common ancestor

The Definition of Evolution

Evolution is the change in allele frequencies, or a change in the gene pool, of a population.

*These changes may not be visible, they occur at the DNA level

Important Points

Selection Strength

How does the environment push for the survival or elimination of a polymorphism?

Stickleback Fish

(Video: Meet the Three Spine Stickleback)

The armored plating on ocean fish is a disadvantage in freshwater. 

The plates make it easy for aquatic invertebrates (dragonflies) to grab young fish.

In the ocean, the plates help the fish survive large predators.

Rock Pocket Mouse

(Video: Natural Selection and the Rock Pocket Mouse )

Light colored mice are more likely to inhabit areas where there is light colored sand
Dark colored mice are more likely to inhabit areas where there are dark rocks.

Predatory birds hunt by sight, mice that don't blend in are easy targets.

Both mice have white bellies, because that doesn't impact their survival.

What about Giraffes? How did they get their long necks?

What selective pressure may account for the long necks (and legs) of giraffes?

Giraffes with long necks survived and passed their genes to offspring. Overtime, the population had individuals with long necks.

How does natural selection explain the many subspecies of giraffes?

The subspecies may be the result of differing selective pressure, but are most likely the result of genetic drift.

Divergent Evolution - many species arise from a common ancestor (finches)

Convergent Evolution - unrelated species share features that are adaptations for a particular environment (sharks and dolphins)

Phylogenetic Trees - show relationshiips

camel phylogeny

Anoles and Natural Selection

Lizards in a Hurricane

Lizards in the Cold