CHAPTER 15 NOTES EVOLUTION

EVOLUTION –

change over time

CHARLES DARWIN

Contributed more to our understanding of evolution than anyone

Journeyed around the world on the HMS Beagle and made observations and collected evidence Collected fossils (preserved remains of ancient organisms) The islands that influenced Darwin the most were the Galapagos Islands (a group of islands with very different climates)

Darwin on HMS

Beagle – A 5 year trip

Darwin’s Observations

Darwin was intrigued by the fact that so many plants and animals seemed remarkably well suited to whatever environment they inhabited.

He was also puzzled by where different species lived – and did not live.

He soon realized that living animals represented just part of the puzzle posed by the natural world.

The Galapagos Archipelago

Marine Iguana Land Iguana

Darwin learned that the giant tortoises varied in predictable ways from one island to another.

The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

Darwin later admitted in his notes that he “did not for some time pay sufficient attention to this statement.”

One tortoise from an island with sparse vegetation has a long neck and shell that is curved to reach.

Another tortoise has a dome-shaped shell and a shorter neck because vegetation on this island is more abundant and easier to reach.

Another tortoise has a shell that is intermediate between these two forms.

Darwin Gathers More Evidence

English animal breeders were selectively breeding birds to get large, colorful feathers for ladies hats.

This was a type of “

artificial selection

” because the breeders were controlling which traits were crossed.

Darwin wondered if some force in nature also selected which organisms would survive.

Results of Artificial Selection

Other Scientists that influenced Darwin:

1. Hutton & Lyell studied geological change to show that the Earth changes over long periods of time

2. Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone (war, famine and disease help keep this growth in check)

3. Lamarck was the first scientist to recognize that living things change over time

Lamarck’s ideas:

1. Organisms constantly strive to improve themselves (tendency toward perfection) 2. Most-used body structures develop, but unused ones waste away (use and disuse)

3. Once a structure is modified by use or disuse, the modification is inherited by the organism’s offspring (

inheritance of acquired characteristics

long necks.

) A giraffe’s neck gets long because he reaches. His offspring inherit the

ALL OF THESE WERE PROVEN WRONG, but Lamarck paved the way for the work of later biologists.

Darwin’s Grand Idea

Darwin spent over 20 years gathering facts that might have some bearing on how species originated.

Putting all of his amassed data together, Darwin developed his grand idea.

Darwin didn’t go public with his ideas because the dominant philosophy of his day placed the most value on gathering facts, not on hypothesizing.

Darwin’s Dilemma

On June 18, 1858, Darwin received a letter from a fellow scientist,

Alfred Russell Wallace

.

In the letter was an abstract of a theory of evolution that Wallace was about to publish.

He was asking Darwin for a peer review of his theory before submitting it for publication.

Alfred Russell Wallace (1823 1913)

Darwin & Wallace

Wallace’s theory was exactly the same as Darwin’s!

Darwin was ready to concede, but mutual friends encouraged Darwin & Wallace to allow their theory to be jointly presented.

Thus, on July 1, 1858, their theory was jointly presented to the

Linnaean Society of London.

Charles Robert Darwin in 1859

Darwin Gets Credit

Darwin is given primary credit for the theory of evolution by natural selection because: (1) he had collected more evidence than Wallace and (2) he had written, but not published, a general outline and an essay on evolution at an earlier date (1844).

Although controversial, many prominent scientists supported Darwin & Wallace.

Darwin’s Book

The following year, 1859, Darwin published his full theory with evidence.

The title was:

On The Origin of Species by Means of Natural Selection

. All 1,250 copies of the first printing were sold on the first day!

“Survival of the Fittest”

In 1866, the English philosopher

Herbert Spencer

, in an attempt to explain what Darwin meant by the struggle of organisms in nature, coined the phrase “

survival of the fittest

”. The phrase is often attributed to Darwin but it does not appear in any of his writings.

Definitions:  Variation – differences between individual members of a population (ex. Color of fur, shape of teeth)  Adaptation – an inherited characteristic that increases an organism’s chance of survival

Darwin’s Theory of Natural Selection:

1. There is variation within a population.

2. Some variations are favorable.

3. Not all young produced in each generation can survive. (struggle for existence)

4. Individuals that survive and reproduce are those with favorable variations (survival of the fittest)

5. All species have common ancestors. (Descent with modification)

EVIDENCE OF EVOLUTION

According to evolutionary theory, all life originated from a common ancestor. Common descent – the theory that all species were derived from common ancestors

WAYS TO DETERMINE HOW RELATED ORGANISMS ARE:

1. Fossils

The fossil record reveals changes in populations over time and supports the theory of evolution.

Scientists can calculate a fossil’s age by using radioactive dating or relative dating (we will discuss this later)

The fossil record is incomplete, but it still shows us relationships between species and how their structures have changed over time.

Fossils are mostly found in sedimentary rock.

2. Homologous Structures

Homologous structures – structures that have different mature forms, but develop from the same tissues Ex. Arms, wings, and flippers are all constructed from the same basic bones

Homologous Structures

Flying Swimming Running Grasping

3. Vestigial structures – structures reduced in size and often unused Ex. Leg/hip bones in pythons and whales or appendix in humans

4.

Embryology & Biochemistry

Embryology – compare how embryos of different species look during certain stages of development

Biochemistry – compares the biochemicals that make up our body (amino acid)

Comparison of Organisms Two orders of mammals Birds vs. mammals Amphibians vs. birds Fish vs. land vertebrates Insects vs. vertebrates Algae vs. animals Percent Substitutions of Amino Acids in Cytochrome c Residues 5 and 10 8-12 14-18 18-22 27-34 57

The Fact of Evolution

Darwinism is not “just a theory” as many believe. Darwin’s conclusion that species change over time is a

scientific, proven fact

.

The mechanism suggested by Darwin for that change,

natural selection

, is a

theory

.