one of the most respected evolutionary biologists has defined biological evolution as follows: ...

One of the most respected evolutionary biologists has defined biological evolution as follows:

"In the broadest sense, evolution is merely change, and so is all-pervasive; galaxies, languages, and political systems all evolve. Biological evolution ... is change in the properties of populations of organisms that transcend the lifetime of a single individual. The ontogeny of an individual is not considered evolution; individual organisms do not evolve. The changes in populations that are considered evolutionary are those that are inheritable via the genetic material from one generation to the next. Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest protoorganism to snails, bees, giraffes, and dandelions."

- Douglas J. Futuyma in Evolutionary Biology, Sinauer Associates 1986

Evolution and Populations It is important to note that

biological evolution refers to populations and not to individuals and that the changes must be passed on to the next generation.

In practice this means that evolution is a process that results in heritable changes in a population spread over many generations.

Competing TheoriesCompeting Theories

Lamarck’s Theory of Evolution

Proposed in 1809, Lamarck observed that characteristics of living things could change over time.

For example, if muscles are used, they grow stronger. These are called “acquired” characteristics.

Competing TheoriesCompeting Theories Lamarck’s Theory of Evolution

Lamark proposed that organisms can pass on these acquired characteristics to their offspring.

For example: Ancestors of giraffes had short necks. Lamark’s theory goes that since they had to stretch to get food, their necks became longer and they could pass this trait to their offspring.

Competing TheoriesCompeting Theories

Competing TheoriesCompeting Theories

Even though the giraffe's neck is extremely long, it has only seven neck vertebrae, the same number that people and most other mammals have.

Definition of Evolution:

The accumulation of changes in the heritable characteristics of a populationpopulation.

Evolution describes the changes in the various genes of a species over time.

These changes are the result of:MutationsNatural selectionChance

Voyage of the Beagle, 1831-1836

Succession of Types

Why should extinct armadillo-like species and armadillos be found on the same continent?

The changes imply ancestry!The changes imply ancestry!

“This wonderful relationship in the same continent between the dead and the living will, I do not doubt, throw more light on the appearance of organic beings on our earth, and their disappearance from it, than any other class of facts.”

--The Voyage of the Beagle, ch. 8

Basic Tenets of the Theory of Evolution:

1. Populations tend to produce more offspring than the environment can support.

• This leads to a struggle for existence in which some individuals survive and some die.

Carrying Capacity

2. Natural Selection2. Natural Selection Definition:

The over-production of offspring leads to competition and survival of the individuals best suited to that particular environment.

The better adapted individuals tend to survive and reproduce more than the less well-adapted individuals.

3. The variation in individuals in a population is controlled by their genes and is therefore inheritable.

The better adapted individuals pass on their characteristics to more offspring than the less well adapted.

The results of natural selection therefore accumulate. As one generation follows another, the characteristics

of the species gradually change.

How Does Variation How Does Variation Arise?Arise?In the DNA:In the DNA:

--Sexual ReproductionSexual Reproduction

--MutationsMutations

In the Environment:In the Environment:

--Genetic Drift Genetic Drift

Variation is non-directional (random)

Sexual Reproduction Role: Promotes variation in a species

through meiosis and fertilization which is essential to natural selection.

Mutations:Mutations:

Changes in the base pair sequence of DNA.

Most are neutral or harmful to the organism, but some have positive effects.

Note: In an organism that sexually reproduces, the mutation must occur in a gamete (sex cell) if it is to be passed on to offspring, and thus contribute to the evolution of that organism.

A mutation has caused the garden moss rose A mutation has caused the garden moss rose to produce a flower of a different color.to produce a flower of a different color.

The selection process is directional:

It is dictated by the environment (not random).

This leads to differential survival:The result is that the

individuals best adapted to a specific environment will survive to reproduce.

What are some things you think these organisms can do better than others?

Differential Survival:

If environments change (either gradually or suddenly), the “best adapted” may also change.

This process can lead to changes in the species

Genetic Drift: Sometimes the

frequency of a gene in a population is determined by by chancechance and not by whether it gives the individual an advantage in the environment.

This is known as genetic drift.

Populations: It is important to know at

this point that evolution doesn’t work on the level of individuals or species- it works on the level of populations.

Thus, individuals do not evolve, populations do.

Explain why evolution works on populations and not individuals.

Speciation When two groups of

a species are in different environments they cannot interbreed.

If the selection pressure is different, they will eventually become different species: aka speciation.

The eastern meadowlark (Sturnella magna) and the western meadowlark (Sturnella neglecta) have very similar body shapes and coloration.

Their ranges overlap in the middle of the country.

Considered different species: Songs are different Behavioral differences that prevent

interbreeding.

In the summer of 1995, at least 15 iguanas survived Hurricane Marilyn on a raft of uprooted trees. They rode the high seas for a month before colonizing the Caribbean island, Anguilla. These few individuals were perhaps the first of their species, Iguana iguana, to reach the island.

Speciation:

Artificial SpeciationArtificial Speciation

Allopatric speciation of squirrels in the Grand Canyon

Harris’s antelope Harris’s antelope squirrel (south rim)squirrel (south rim)

White-tailed White-tailed antelope squirrel antelope squirrel (north rim)(north rim)

Ex. Many of the finches in the Galapagos islands.

Why are finches different on different islands?

Islands have different kinds of seeds available which select for different types of beaks to eat them.

In time the birds become so genetically/physically different they cannot interbreed.

Environments constantly change and if a species cannot adapt, they may go extinct.

Ex. Dinosaurs Couldn’t adapt to

colder climate Their place was

taken by mammals (homeothermic-warm blooded)

Not all dinosaurs went extinct. Some also evolved to become warm-blooded birds.

There have been 5 major extinction events during the history of life on Earth.

The The Cretaceous-Cretaceous-Tertiary Extinction Tertiary Extinction (65.5 MYA) is (65.5 MYA) is probably the most well probably the most well known, as it killed off known, as it killed off all all non-aviannon-avian dinosaurs. dinosaurs. 7575% of all % of all species went extinct.species went extinct.

Some 99.9% of all species that have ever lived on Earth are now extinct.

There have been 5 major extinction events during the history of life on Earth.

This wasn’t even the largest though. That honor goes to This wasn’t even the largest though. That honor goes to the the Permian-Triassic ExtinctionPermian-Triassic Extinction (251 MYA) which caused (251 MYA) which caused the extinction of the extinction of 9696% of all marine species and % of all marine species and 7070% of % of all land species. all land species.