Unit 3

In Unit 3 we look at how life developed on Earth and how organizms change over time due to genetics.

Scientists look at fossils and other clues to figure out how extinct organisms looks, moved, and behaved. Read more here.

How do we know that dinosaurs looked like.

Fossils give us clues about the organisms that lived in the past.

There are 5 main types:

Petrified Fossils (which are what we often think of when we discuss fossils) occur when minerals replace all or part of an organism.

Molds and Casts occur when the hard part of an organism disolves leaning a hollow in the ground that is the shape of the organism. Water and minerals move into these holes filling the space.

Carbon Films occur when most of an organism beaks down and only the carbon remains.

Trace Fossils are marks such as footprints or burrows that shows the activities of the organism.

Preserved remains (such as frozen wooly mammoths or organisms in amber) are the actual organisms, preserved in a way that keeps them even when they normally would have decomposed.

Natural Selection is the process by which organisms acculumate beneficial traits over time to help them better survive in their environment.

This is also known as survival of the fittest which means that organisms best fit or best able to survive and have offspring will pass on their positive traits to their offspring and organisms that are less fit are less likely to pass on their negative traits.

Natural selection over many, many generations can result in new and different species.

Over a shorter period of time natural slection selects for existing traits that change an oranism to help it fit into its environment.

This is called microevolution and we see it happen all the time. Above shows a series of pictures that represents this process.

Evidence for Evolution

There are five main things scientists look at to support evolution:

* The fossil record which suggests progression in the development of organisms over time

* Comparative anatomy and homologous structures which suggest common ancestors among seemingly unrelated organisms

* Vestigial structures (which are things like the hip bones in whales) that serve no purpose in organisms and suggest they evolved from an organisms that used those structures

* DNA, the fact that all organisms not only share the same DNA bases, but share most of their DNA as well suggests a common ancestor between them

Macroevolution

When we look at the fossil record we see evolution of macroevolution, or large scale evolutionary changes that can lead to a new species. The picture below represents the evolution of the many of the organisms we see today. Where the tree branches it represents a common ancestor. After shows where that species diverged or changes as new traits evolved.

Microevolution

There is also something called microevolution, these are changes within a species over a short period of time.

As organisms with certain traits survive better, such as the greener frogs in the picture above, this trait becomes more common in the population.

Microevolution is similar to the selective breeding we do with organisms. Two examples are dogs being breed from wolves and all the varieties of brassica or mustard (such as broccoli, brussel sprouts, kale, and more) we breed from wild mustard.

In each case we selectivelly breed organisms that had traits we liked to create an organism that is still the same species, but looks different from the parent variety.

The different proteins your cells produce help make up your cells and tissues and also help your body's biochemical reactions. However, sometimes your DNA changes, altering what proteins are made. The things that make you different from those around you are due to mutations.

There are different types of mutations, some of which are silent or don't have a change, others which cause you body to make different or incorrect proteins.

Mutations can be seen as good, bad, or neutral depending on how they impact an organisms survival.

An example of a mutation is albinoism. This mutation impacts your body's ability to make an enzyme (a type of protein) that is needed to produce melanin (what gives you skin, hair, and eyes color).

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