EvolutionWhat We Now Know

CreationismThe traditional Judeo-Christian version of creationism was strongly reinforced by James Ussher , a 17th century Anglican archbishop of Armagh in Northern Ireland.  By counting the generations of the Bible and adding them to modern history, he fixed the date of creation at October 23, 4004 B.C. 

Evolution

The Creation of Adam is a section ofMichelangelo’s fresco on the ceiling of the Sistine Chapel painted in 1511.

Evolution is the process in which significant changes in the inheritable traits (genetic makeup) of a species occur over time.

What evidence supports this change of thinking?

1. Fossil Evidence

- Shows a record of the diversification of species

- It also shows the record of the extinction of many others.

Mass ExtinctionsWhy are mass extinctions important?

They stimulate new biodiversity!

No competition.

geographic distribution of living species gave scientists clues to the patterns of evolution

1. Fossil Evidence

- Shows a record of the diversification of species

What exactly is a fossil:

- Any preserved remains or traces of an organism or its activity.

- In 1669 Nicholas Steno detailed an impressive analysis of fossils showing that they were the remains of living organisms

- fossils form in sedimentary rocks

How does a fossil form? Organisms must die and then be rapidly buried to prevent scavengers or

rapid decomposition (if there are only soft parts).

There are two types of fossils:

Body Fossils which are actual remains:

Includes actual bones, shark’s tooth, petrified wood, frozen mammoth, insects in amber.

Trace Fossils which include: Mold or Cast formed by replacement

Or footprints, worm trails, coproliths, or stomach stones

Ages of Rocks Relative Age – age of rocks and the relative age of fossils can be

determined by the chronology of the rock layers. Oldest on bottom, youngest on top.

Absolute Age – determined by radioactive decay (radioactive dating using half lives)

C14 has a half life of 5730 y

K 40 has a half life of 1.3 b.y.

Charles LyellProposed that the earth’s surface has changed

and continues to change through similar gradual processes.

1851 visited Joggins

Index FossilsUsed to determine ages of rock layers

Examples of index fossils:Short lived, easy to identify

2. Structures – Homologous and

AnalogousHomologous- structures that share a common

origin but may serve different functions in modern species

Long bone

Two short bones

Example of Homology:

the tetrapod limb

The wing of a dragonfly and the wing of a butterfly are homologous — they were both inherited from an ancient flying insect.

Not all homologies are obvious if they have been adapted for different roles. For example, the chomping front teeth of a beaver look quite different than the tusks of an elephant. Each is a modification of the basic incisor tooth structure

Homologies show that Divergent Evolution takes place

Divergent Evolution: A common ancestor evolves into new species, which continue to evolve and become less and less alike over time due to differences in the demands driven by the environment.

Brown Bears and Polar Bears illustrate divergent evolution.

Scientists think that a long time ago a group of Brown Bears became geographically separated from the rest. This isolated group acquired new characteristics, such as the ability to eat meat, blubber to keep warm in snowy weather, and a white coat for camouflage. They slowly evolved into Polar Bears

Analogous – structures similar in function but not in origin

So what about ANALOGY?? Consider the following example....

Both are extinct animals and both of them have saberteeth...but are they homologous??(Consider that Australia had separated from the Supercontinent a loooooong time ago)

Thylacosmilus, a marsupial mammal

Smilodon, the saber-toothed cat, which is a placental mammal

They are Analogous!

analogysimilarity due to convergent evolution not common ancestry

CONVERGENT Evolution: When two separate groups of animals evolve to have similar structures

How do analogies evolve?Often, two species face a similar problem or challenge. Evolution may then shape both of them in similar ways — resulting in analogous structures.....like the saber teeth.

Another good example of Analogous structures......

While sugar gliders (marsupials) superficially resemble the placental flying squirrels of North America, the ability to glide through the air evolved independently in these unrelated mammals.

So there you have it.....HOMOLOGY vs. ANALOGY

Embryonic Development – Embryos of different organisms can have homologous features

Human embryos have a tail

Vestigial Features- Structures which serve no useful function in a living organism

Digits (dogs)

Hipbones (whales)

Now the evidence continues

Lamarck – each species gradually became more complex and that new simple species were created by spontaneous generation (He did not believe that a single species could give rise to additional species (no common ancestor)).

- He believed in the inheritance of acquired traits (changes in an individual resulting from interaction with the environment) Giraffe’s with longer necks (acquired trait inherited by the offspring)

- -now know that acquired traits cannot be inherited

- -he does deserve credit for his recognition of the role of the environment in driving evolutionary change

“Use and Disuse” – CHARACTERISTICS that were in constant use developed (were ACQUIRED) and those that were not used were LOST.

Wallace Vs. DarwinDarwin always put the emphasis on selection acting

on individuals whereas Wallace (the letter writer) apparently thought selection acted on groups or species. That selection acts on the individual, due to competition between individuals of the same species, is one of the key points in Darwin’s theory.

Another apparent difference is that Darwin emphasised competition within populations as the driving force for evolution wheres Wallace put more emphasis on the species meeting the demands of a change in their environment.

Darwin…..Set sail in 1831 on the HMS Beagle

Voyage lasted 5 years

He recorded and collected specimens in South America

Reached the Galapagos Islands and noted that the flora and fauna although similar to South America, also had unique traits

Darwin came to the conclusion that perhaps a single ancestral species transported from a single nearby island might give rise to a number of similar but distinct new species

Adaptive Radiation is an example of Divergent evolution (remember the bears) but happens more quickly

Consider Darwin’s finches...each evolved a new beak to fill a wide range of ecological niches...or ADAPT.

How did one species of finch become so many species?http://www.youtube.com/watch?v=l25MBq8T77w&feature=related

Darwin’s finches had differences in their beaks.

Beaks are associated with eating different foods.

Darwin’s conclusions:

Small populations of original South American finches land on islands. The variations in the beaks allowed individuals to gather food successfully in different environments.

Over generations, the population of finches changed both anatomically and behaviorially.

New Species emerged.

The most recognized symbol of the Galapagos is the tortoise. When Charles Darwin visited the Galapagos Islands, the vice-governor of the Islands told him that he could identify what island the tortoise was from simply by looking at him.

Artificial Selection Vs. Natural Selection

Darwin believed that there must be a mechanism of inheritance that would provide the key to the evolutionary process.

He studied the structures, functions and behavior of species.

He also looked for evidence of changes in populations of organisms that were reproducing.

Humans have been improving domesticated plants and animals species for thousand of years.

Offspring are selected with desirable traits as breeding stock of the next generation

Selective breeding techniques have led to these genetically superior beef cattle that have incredible muscles and strength known as “Belgian Blue”. Modern breeds of Belgian Blue cattle are the creation of genetic engineering, with the specific goal of expanding the muscular content of the animals as much as possible.

http://www.youtube.com/watch?v=Nmkj5gq1cQU&feature=related

Useful Selective Breeding

Artificial selection has been used in modern farming to get:

- The best beef cattle – taste and texture

- The best milking cows – yield and disease resistance

- Wheat – better yields and disease resistance

- Flowers – bigger and more colourful

- Chickens – egg size and number

Natural SelectionThomas Malthus – postulated that in nature, plants

and animals produce far more offspring than are able to survive.

Darwin realized that if far more offspring are born than can survive and reproduce, there must be intense competition among the individuals to survive. “Survival of the Fittest”.

The mechanism causing evolution was natural selection. All species exhibit inheritable variations that are selected through the struggle by individuals for survival within their populations.

Individuals with more favourable traits produce more offspring that survive than others and pass along those favourable traits. Over many generations this process results in change in the inheritable traits of the population.

On November 24, 1859

Darwin published “On the

Origin of Species”

(prompted by a letter

from Alfred Russel Wallace who

had come up with the

same idea).

A Summary of Darwin’s Ideas (Steps of Natural Selection)

1. Many more offspring are born each season than can possibly survive to maturity. As a result, there is a struggle for existence- competition.

2.Individual variation exists in natural populations.

3. Individuals with advantageous variations survive and pass on their variation to the next generation.

4. Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the average characteristics of the population (adaptations).

Over long periods of time, and given a steady input of new variations into a population, these processes lead to the emergence of new species.

http://www.overman.info/evolutionrocks.html