Darwin and Evolution

“There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

-Charles Darwin, On The Origin of Species, 1859

Do NOW!

What happens when specific traits are passed down through many generations?

Charles Darwin• Born February 12, 1809

• Died on April 19, 1882

• Darwin’s father decided his son should study for the clergy at Cambridge - a very respectable profession in the early 1800's.

• Beetle collecting during his time at Cambridge taught Darwin many vital scientific skills, which included: how to identify species, the proper manner of cataloguing specimens, methods of comparative anatomy, and how to work efficiently in the field.

Darwin's Importance

• 1831-1836 sailed on H.M.S. Beagle - Originally the ship's geologist, eventually also naturalist (studied living things & environments)

Darwin's Importance

What to do with his collections?

• Between 1836-1837, Darwin observed, catalouged, and wrote papers about the specimens that he collected while on his trip. This time period is what lead him to the idea of a “transmutation of species”.

• Transmutation of species was a term used by Jean Baptiste Lamarck in 1809 for his theory that described the altering of one species into another.

Transmutation of Species• 1837 around July

Darwin began his "B" Notebook in which he put down his thoughts on the subject of transmutation. In this notebook Darwin examined four general questions --

- what was the evidence for species transmutation? - how did species adapt to a changing environment? - how were new species formed? - how one could account for the similarities between different species?

One of the highlights of the B Notebook was his analogy of a branching tree to represent common descent of all species.

The struggle for survival…

• 1838 OctoberDarwin read a book by the famous economist, Revd. Thomas Malthus, titled "Essay on the Principle of Population." In this book Malthus put forward the economic theory that as human populations grow and resources become scarce the weak die off in a struggle for existence. Darwin theorized that the same kind of relationship may exist in the wild. In other words, what Malthus saw in economics, Darwin saw in nature.

To publish or not to publish?

• 1842Darwin made an outline of reasons not to published his transmutation ideas -

[1] Fellow naturalists would never accept his ideas. [2] animal breeders would find a huge treatise too boring to read. [3] the trouble making atheists would use it for their evil agendas. [4] the church would scorn him. [5] he did not want to be labeled an atheist. [6] he would betray his friends and family to whom he owed so much.

• 1854 DecemberAt last Darwin figured out how populations split off into separate species. Using the industrial revolution as a metaphor, he saw that populations of animals, like industry, expand and specialize to fit into niches with competition acting as the driving force. He saw nature as the ultimate "factory." However, Darwin preferred not to make much of this metaphor because it seemed to depend more on economic principles rather than pure science.

• 1858 June 18Darwin received a paper from Alfred Russel Wallace, who was still at the Malay Archipelago. The paper was titled: "On the Tendency of Varieties to Depart Indefinitely from the Original Type." Darwin was shocked! Wallace had come up with a theory of natural selection that was very similar to his own. The paper contained concepts like "the struggle for existence," and "the transmutation of species."

• 1859 November 2While at Ilkley Spa Darwin received an early copy of his book, "On the Origin of Species by means of Natural Selection."

The title for "Origins" went through a few changes while it was being written:

-- An Abstract of an Essay on the Origin of Species and Varieties through Natural Selection. -- On the Origin of Species and Varieties by means of Natural Selection. -- On the Origin of Species by means of Natural Selection.

1860 JanuaryThe repercussions of Origin of Species were mixed.

Thomas Huxley and Joseph Hooker thought very highly of it and soon became stronger allies with Darwin. Huxley soon became a ruthless defender of evolution, even going so far as to suggest that mankind was a transmuted ape!

Richard Owen was outraged by the Origin. He saw the ideas expressed in the book as being dangerous to society. He also thought the book left too many unanswered questions, and worst of all it leaned natural science away from its respectable position as an investigator of god's creation. Most readers, however, simply did not understand how natural selection worked. They could not see who or what was doing the selecting. Many assumed god was the selector.

Darwin wondered: Why were these animals different? Why would they have these obviously different characteristics if they were similar organisms?

Differences in Similar Organisms Darwin observed similar organisms on

mainland South America and the Galapagos Islands

Examples:

Cormorants: on the mainland, these could fly, but the species that lived on the islands was flightless

Tortoises: each island had a species of giant tortoise, but the shape of their shells varied on each island;

Darwin could identify which island the tortoises came from just by looking at their shells.

Iguanas: on mainland they had small claws to climb trees and ate cactus & flowers while island iguanas could swim, had long claws to grip rocks and ate seaweed

Adaptations

• These differences are called adaptations

• In order to survive in different places, the original organism had to change

• This change was not a choice, but through genetic diversity

Cormorants: no predators, everything they needed was close to the ground, therefore, they lost the ability to fly

Loss of flight is an adaptation.

Darwin's FinchesFinches on different islands have different

beaks. Why????Beak type depends on the food available. Finches that are adapted to eat the available food on their island will survive long enough to reproduce. This will pass the trait for the beak that is best suited for survival in that area.

Different Beaks

Natural Selectionthe idea that animals that are better adapted for a particular environment will survive, reproduce and pass on these desirable attributes to the next generation

Natural Selection• overproduction- producing many

more offspring than will survive; crabs & fish lay thousands of eggs, but only a few will become adults. What happens to the rest???

• competition- "fighting" for available resources (food, shelter, mates). Those that are not successful will die, those that are will reproduce. Do you see a pattern here? Why do organisms want to survive???

Natural Selection

variation- differences among individuals in the same species or group. Good variations help an organism survive better and are kept through reproduction. Bad variations that are not helpful are lost, because those organisms do not survive to reproduce and pass on the traits.

• Differential survival and reproduction - Individuals with the most successful adaptations to their environment are most likely to survive and reproduce. Over generations the character of a population changes as the frequency (how often it is available) of a trait increases or decreases.

Can you Spot the moths?

Adaptations work by mutations. If a mutation in an individual helps it to survive, it will survive and reproduce, passing the gene for the mutation on to its offspring.

Species have three “choices”: Go extinct in that area. Move to another area (emigrate). Adapt to survive the stress.

Darwin wondered: So what is evolution anyway? What evidence suggests this process?

Evolution• Many generations of

natural selection lead to permanent changes in a species. This is called evolution and occurs gradually over time.

• Different organisms have different rates of evolution, depending on their life spans.

Evolution

All organisms evolve- insects, mammals, bacteria, plants and fungi.

• The central ideas of evolution are that life has a history—it has changed over time—and that different species share common ancestors.

• evolutionary change and evolutionary relationships are represented in “family trees,” and affects biological classification.

Evolution is a theory- which is an idea supported by a large amount of evidence.Darwin's observations are the beginning of this evidenceMany others have added to his work

Natural Selection

Evolution

New Species

Modes of Speciation

• Ecological opportunity

• Geographical Isolation (allopatry)

• Founder Effect

• Genetic Drift

• Speciation by Hybridization

• Intense Competition

• Adaptive Radiation

• Cospeciation

geographic isolationwhen a group of organisms is separated from the rest of its species long enough, it gains new adaptations for survival

*** some characteristics will be similar, but usually new adaptations will will make it different enough to be considered a new species

continental drift-

when an entire area is isolated, preventing migration or movement of animals; specific & unique features develop as a result

*** After Pangea, organisms that started out similar and adapted to survive on these "new continents", forming very specific species on each

Example: Australia has kangaroos, echidnas & goannas

• DNA sequence, genotype, & phenotype • In the example to the right, these driftworms have a

single gene, the Color gene. The DNA sequence for this gene is 9 base pairs long.

• There are five phenotypes for this gene -- pink, blue, navy, green and yellow. Each phenotype has a different genotype. The genotypes are different from one another because their DNA sequences are different. These different genotypes are referred to as alleles.

Genetic Drift

The role of chance • In real life, some individuals have more offspring than

others--purely by chance. The survival and reproductions of organisms is subject to unpredictable accidents. It doesn't matter how good your driftworm genes are if you get squished by a shoe before producing offspring.

• An ant gets stepped on. • A rabbit gets swept up by a tornado. • An elephant drinks up a protozoa living in a puddle. • A plane crashes killing a Nobel Laureate.

• None of the above events has anything to do with the dead organism's genotype or phenotype--these events occurred purely by chance.

Fixation of an allele • In a population model with genetic drift, alleles

will eventually become "fixed". When an allele is fixed, all members of the population have that allele. In the graphic below, note that the dark blue allele fixed after 4 generations.

Speciation is integral to the evolutionary process:• Natural selection shapes most evolutionary

adaptive change nearly simultaneously in genetically independent lineages as speciation is triggered by extinction in “turnover” events.

• When physical environmental events that go “too far too fast” start triggering regional, species-level extinction, then evolutionary change — predominantly via speciation — occurs.

• In times of environmental normalcy, speciation and species-wide evolutionary change are comparatively rare.

Key points:

How do we know all of this???

Sloths- Darwin found fossil sloths in South America, but they were MUCH larger than the living specimens he saw in the jungles

Sharks- aside from being smaller, sharks haven't changed much in the last 100 million years...we know this from fossil evidence:)

Fossil records of past creatures & plants...we can examine them and compare them to organisms living today to look for similarities

Homologous structures-structures that serve a similar purpose in organisms that share ancestors

Examples:

Natural Selection

Ernst Mayr• A species consists of a group of populations which replace

each other geographically or ecologically and of which the neighboring ones intergrade or hybridize wherever they are in contact or which are potentially capable of doing so (with one or more of the populations) in those cases where contact is prevented by geographical or ecological barriers (MAYR 1940, p. 256).

Evolution Now?

Theodosius Dobzhansky • He is also known for his study

of the fruit fly Drosophilia, which showed a large degree of genetic variation within a population.

• "The clear-cut mutants of Drosophila, with which so much of the classical research in genetics were done, are almost without exception inferior to wild-type flies in viability, fertility, longevity."—*Theodosius Dobzhansky, Heredity and the Nature of Man (1964), p. 126.

In 1953 published a small volume, Evolution and Geography, that climaxed a series of writings published over more than a decade, all of which addressed the principles for explaining the past distributions of land animals, especially mammals of the Cenozoic Era, representing the last 65 million years of Earth history.

George Gaylord Simpson

Leigh M. Van Valen proposed the Red Queen hypothesis (1973) as an explanatory tangent to the Law of Extinction. The Red Queen hypothesis captures the idea that there is a constant 'arms race' between co-evolving species. Its name is a reference to the Red Queen's race in Lewis Carroll's Alice Through the Looking Glass, in which the chess board moves such that Alice must continue running just to stay in the same place.