MicroevolutionChapter 16 and 17

Evolution

• The change in a species over time.

• The processes that have transformed life on earth from it’s earliest forms to the vast diversity that characterizes it today.

Early Ideas About Evolution

• Many of the early ideas regarding the existence of living organisms were strongly influenced by religion and philosophy.

• However, in the 1600s, scholars began a revolution that created the basis of empirical and scientific thought.

Early Ideas About Evolution1. Hippocrates

– Proposed that all things can be traced to preceding causes.

2. Aristotle– Believed that each kind of organism was distinct

from all the rest.– Classified organisms into two groups: plants and

animals

3. Georges de Buffon (1700s)

– proposed that species shared ancestors instead of arising separately.

– Suggested that Earth was much older than 6000 years

4. Jean Baptiste Lamarck (early 1800’s)

– Proposed that all organisms evolved toward perfection and complexity.

– theory of inheritance of acquired characteristics- changes in an environment caused an organism’s behavior to change, leading to greater use or disuse of a structure or organ.

• For example the giraffe: short neck giraffes needed to reach leaves higher in trees, so they stretched their neck to reach them.

• This stretched neck was passed on to offspring, who in turn, stretched their own necks and passed on that neck to their offspring.

5. James Hutton (late 1700s)– Proposed that the changes in landforms resulted from slow

changes over a long period of time (Theory of Gradualism).

6. Georges Cuvier (early 1800s)

proposed the Theory of Catastrophism - natural disasters have shaped landforms and caused species to become extinct.

7. Charles Lyell (1830s) Proposed the Theory of Uniformitarianism -geologic processes that shape Earth are uniform over time.

Struggle for SurvivalThomas Malthus

-proposed that resources such as food, water, and shelter were natural limits to population growth.

-Human population would grow uncontrollably without limits.

As a result, Darwin suggested that-A similar struggle takes place in nature.-Resources are limited, and organisms had more offspring than could survive.

Charles Darwin• “Father of Evolution”

• Influenced by Charles Lyell who published “Principles of Geology”.

• In 1831, Darwin, on the ship HMS Beagle, set sail from England to map the coast of South America.

• While on the Galapagos Island, he observed the following:1. Species found on one island differed from those

on nearby islands. (Variation)2. Some differences seemed well suited to the

animals’ environments and diets.3. Fossils provided evidence of species changing

over time.4. Fossils suggested that modern animals might be

related to fossil forms.5. Fossil shells of marine organisms were found

high up in the Andes mountains.

After his voyage

• When he returned in 1836, Darwin began discussing his ideas with other scientists.

According to Darwin’s ideas, evolution occurs from generation to generation due to two interacting factors:

1) Genetic Variation Differences occur among individuals of a given

species.

2)Natural Selection In each generation, many more offspring are

produced than will survive. Individuals with more favorable traits will be better suited for the environment. Over time, favorable traits will become more prevalent in a population.

Artificial Selection

Darwin noticed a lot of variation among domesticated plants and animals as a result of artificial selection.– process in which humans/breeders choose as

parents those individuals with traits that are desirable from a human perspective.

– the underlying cause of the phenotypic variation is usually related to differences in alleles that determine the trait.

– through the selection of certain traits, breeders can produce a great amount of diversity.

Main Principles of Natural Selection1. Variation

– Differences exist in every population.

2. Overproduction– many offspring raises the chance of survival but results

in competition between offspring for resources.

3. Adaptation– better adapted = better chances of survival.

4. Descent with Modification– Over time, natural selection will result in more

individuals being well suited for the environment if conditions remain favorable.

Natural Selection can occur in several ways:

1)Directional Selection-new allele introduced into a population

by mutation

2) Stabilizing Selection-reduces genetic diversity

3) Diversifying Selection-Likely occur in populations that

occupy heterogeneous environments-so some members are more likely to survive than others.

4) Balancing Selection-maintains genetic diversity

Evidence of evolution

Evidence of Evolutionary Change• Fossil record• Comparative Anatomy• Embryonic development• Studies of natural selection• Selective breeding• Molecular structure (DNA, Amino Acid

sequence)

Fossil Records provide evidence that living things have evolved

Fossils show the history of life on earth and how different groups of organisms have changed over time

Comparative Anatomy

scientific study of comparable body parts in order to identify

similarities and differences.

Homologous Body Structures

Structures that have different mature forms but develop from the same embryonic tissues

e.g. Wing of bat, human arm, leg of turtle

Turtle

Alligator

Bird

Homologous Body Structures

Analogous Structures• Similar features of organisms that evolve

independently.Examples: • Wings structure in various flying animals

– same function but differ in bone structure, wing coverings, shape, and sizes

• fins – Animals such as penguins and fish both have

fin-like structures

Vestigial Structures

• Bones or other structures present in organisms but are reduced in size and function.

Example:– Hind leg and hip bones in whales

Similarities in Embryology• the study of the development

of an embryo from fertilization to the fetus stage.

• In their early stages of development, chickens, turtles and rats look similar, providing evidence that they shared a common ancestry.

Embryological development

Chapter 17

Speciation –Development of new species

Species

• refers to a particular kind of organism.

Ernst Mayr• is used to define characteristics

particular to one kind of animal.• “Species are groups of interbreeding

natural populations that are reproductively isolated from other such groups.”

• Differences in phenotype do not disqualify some members

• Mayr’s definition does not apply to asexual creatures (as they do not have an extensive gene pool – each offspring being a clone of the parent), but it does help classify sexually reproducing organisms.

Extinction

• The irrevocable loss of one species.

• Example – the loss of the dodo bird

Mass Extinction

• Loss of several species at once due to a catastrophic event.

• The loss of dinosaurs could be considered mass extinction.