EVOLUTION

By the end of the lesson (s), I can:

DEFINE the biological process of evolution.

SUMMARIZE the history of scientific ideas

about evolution.

DESCRIBE Darwin’s contributions to scientific

thinking about evolution.

ANALYZE the reasoning in Darwin’s theory of

evolution by natural selection.

RELATE the concepts of adaptation and fitness

to the theory of natural selection.

The Idea of Evolution On Darwin’s travels to the Galapagos Islands he noted

groups of animals.

Noted that tortoises on the same island resembled each other closely, while those from neighboring islands were different

Noticing similarities and differences among many animals as he traveled, he became convinced that organisms had changed over time and he wanted to know why.

The development of new types of organisms from preexisting ones over time is called EVOLUTION.

Modern scientists define evolution as a heritable change in the characteristics within a population from one generation to the next.

Ideas of Charles Darwin

In the 18th century most scientists thought that

all species were permanent and unchanging.

Also they thought that the Earth was only 1000s, not

billions, of years old.

Scientist began presenting evidence that the species

on the Earth have changed over time and more

evidence that the Earth is much older than people

thought.

In the 1800s European scientists began studying the rock layers called strata.

They found that strata were formed as ne layers of rock are deposited over time.

They inferred that in general lower strata were formed first and therefore are older.

Also found that different lock layers hold fossils of different kinds of organisms.

Georges Curvier spent years reconstructing the appearance of unique organisms from fossil records.

He gave evidence that some organisms in the past differed greatly from any living species and that some had become extinct. Meaning that the species is not living anymore after a certain point in time.

He continued to find many sudden changes in the kinds of organisms he found in the strata.

He explained his observations as the idea of catastrophism. The idea that sudden geologic catastrophes caused the extinction of large groups

of organisms at a certain point in time.

This is no longer accepted by scientist but Cuvier contributed to scientific acceptance that geologic change and extinction had occurred.

Charles Lyell shared Cuvier’s ideas but he

thought that the geologic processes that have

changed the Earth’s surface in the past

continued to work the same ways.

Lyell’s idea is uniformitarianism

Darwin read some of Lyell’s work during travels and

was excited to find how well Lyell’s ideas worked with

his own observations and ideas.

Lamarck’s Ideas on Evolution

Jean Baptiste Lamarck also supported the idea

that populations of organisms changed over

time.

His idea of inheritance of acquired characteristics,

while not supported states that individuals could

acquire traits during their lifetime as a result of

experience or behavior; then pass on those traits to

their offspring.

Darwin’s Ideas Descent with modification Describes the process of evolution. He carefully

reviewed evidence that points to the notion that every species, living or extinct, must have descended by reproduction from preexisting species and that species must be able to change over time.

Darwin was not the first person to present this idea but rather was the first to argue that al species had descended from only one or a few original kinds of life

Darwin saw the animals of the Galapagos Islands as evidence of descent with modification.

He noted that the islands are home to 13 similar species of finches. Each bird has a beak that has adapted for a certain kind of food.

Natural Selection

Darwin proposed the theory of natural

selection as the mechanism for descent with

modification.

Darwin carefully thought about the forces that could

cause changes in organisms over time.

Has for major components:

Overproduction

The production of more offspring than can survive to

maturity.

Each female deer has one or more offspring per year

for many years in a lifetime.

This increases the population in a short time. But

each new deer needs food and is also vulnerable to

predators and disease. Therefore not all deer live for

very long.

This thinking was drawn from Thomas Malthus’ work. He

pointed out that human populations can increase more

quickly and that populations are often limited by

conditions such as war, disease, or lack of food.

Darwin realized that environment limits the population

of all organisms by causing death or by limiting births.

Genetic Variation Within a population individuals have different traits.

Some deer have thicker fur or longer legs than

others.

Variations can be inherited and occasionally new

traits appear in a population.

Struggle to survive

Individuals must compete with each other in

what Darwin Calls struggle for existence.

Deer that have thick fur may survive I the cold better

than those without thick fur.

A trait that makes individuals successful in its

environment is called an adaptation.

Differential Reproduction Darwin concluded that organisms with the best adaptations are

most likely to survive and reproduce.

Through inheritance those adaptations will become more frequent in populations.

Darwin used the phrase SURVIVAL OF THE FITTEST to describe natural selection.

Fitness in evolutionary terms is the measure of an individual’s hereditary contribution to the next generation. A FIT individual is one that has offspring that also survive long

enough to reproduce in a given environment.

The term adaptation in evolutionary terms is used to describe changes in traits in populations over time.

Acclimatization is a short-term process in which physiological changes take place in a single being in its own lifetime.

An animal adjusting to a new climate by growing thicker fur.