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

Darwin and Evolution

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

The struggle for survival…• 1838 October

Darwin read a book by the famous economist, Revd.

• Thomas Malthus, titled "Essay on the Principle of Population." – the economic theory that as human populations grow

and resources become scarce the weak die off in a struggle for existence.

– What Malthus saw in economics, Darwin saw in nature.

To publish or not to publish?• 1842

Darwin 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

• 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.“

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. 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.

Warm UP: 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.

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

Darwin was not the first naturalist to think of

evolution…

Jean-Baptiste Lamarck• Change through use and disuse

– When environments changed, organisms had to change their behavior to survive. If they began to use an organ more than they had in the past, it would increase in its lifetime. Meanwhile organs that organisms stopped using would shrink.

• If a giraffe stretched its neck for leaves, for example, a "nervous fluid" would flow into its neck and make it longer. Its offspring would inherit the longer neck, and continued stretching would make it longer still over several generations.

Natural Selection

• overproduction- producing

many more offspring than will

survive

• competition- "fighting" for available resources (food, shelter, mates). Those that are not successful will die, those that are will reproduce.

Natural Selection

Natural Selection

• variation- differences among individuals in the same species or group.

• Differential survival and reproduction - Over generations the character of a population changes as the frequency (how often it is available) of a trait increases or decreases

Natural Selection

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.

• The central ideas of evolution – that life has a history—it has changed over

time– that different species share common

ancestors.– are represented in “family trees,” and affects

biological classification.

The central ideas of evolution • Fitness

– describes the ability to both survive and reproduce, – is equal to the average contribution to the gene pool

of the next generation that is made by an average individual of the specified genotype or phenotype.

Coevolution• The term coevolution is used to describe

cases where two (or more) species reciprocally affect each other’s evolution.

• Coevolution is likely to happen when different species have close ecological interactions with one another. These ecological relationships include:– Predator/prey and parasite/host – Competitive species – Mutualistic species

Example:

Convergent evolution• A kind of evolution wherein organisms

evolve structures that have similar (analogous) structures or functions in spite of their evolutionary ancestors being very dissimilar or unrelated.

Example:

Divergent evolution

• The process of tracing back two or more species to their common ancestor that indicate how they have diversified and diverged.

Example:

Adaptive radiation• The diversification of several new species

from a recent ancestral source, each adapted to utilize or occupy a vacant niche

Example:

WHAT TO DO:• Complete the packet using your notes from today’s

information.

• Using the data table from Friday. Calculate the total number of each color of “worm” collected. (I placed 23 of each color outside). Create a bar graph of how many of each were “captured”.

• Figure the percent of color “captured”.• Which color had the highest percent of capture? Which

one the least? Why?• How does this activity relate to natural selection and

evolution? Which color would begin to increase it’s population size? Why?

WARM UP:

• What are the four types of evolution?

• What are the central ideas of evolution?

Evidence of Evolution: Fossils

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

Evidence for Evolution: Anatomy

Analogous Structures• have the same

function, but not the same structure.

• The bird wing and insect wing are analogous structures.

Homologous structures-structures that share similar bone arrangements and/or function in organisms that share ancestors

Examples:

Evidence for Evolution: Anatomy

Evidence for Evolution: Anatomy

• Vestigial structure: a body structure in a present-day organism that no longer serves it’s original purpose, but was probably useful to an ancestor

Evidence of Evolution: Biochemistry

• Every organism has a specific DNA sequence

• The more closely related organisms are the more similar their sequence is.

• For example a human’s DNA sequence is more similar to a chimp’s than to a frog’s so we are more closely related to chimps than frogs.

Evidence for Evolution:

Embryology

Phylogeny vs. Ontogeny

• Phylogeny: the connections between all groups of organisms as understood by ancestor/descendant relationships

• Ontogeny: a purely biological unfolding of events involved in an organism changing gradually from a simple to a more complex level

Two major hypothesis on how evolution takes place

• Gradualism: the slow and constant change of an organism

• Punctuated equilibrium: species evolved rapidly, then stayed the same for longer periods of time

Two major hypothesis on how evolution takes place

Activity: Examining the Fossil Record

• Follow the directions in the packet.

• Answer the analysis questions.

Natural Selection

Evolution

New SpeciesWarm Up!Explain the diagram above… what does it mean?

Vocab

• Gene pool: all the alleles of the population’s together are referred to as a gene pool

• Allelic frequency: The percentage of any specific allele in a population’s gene pool

Natural Selection Acts on Variations within the gene pool

• The allelic frequencies in a population’s gene pool will change over generations due to the natural selection of variations.

• Three different types of Natural selection that act on variation:– Stabilizing– Directional– Disruptive

Stabilizing selection

• Natural selection that favors average individuals in the population

Directional selection

• Occurs when natural selection favors one of the extreme variations of a trait

Disruptive selection

• Individuals with either extreme of a trait’s variation are selected for.

What is a species anyway?

• A species is often defined as a group of individuals that actually or potentially interbreed in nature.

Defining Speciation• Speciation is a

lineage-splitting event that produces two or more separate species.

Speciation Example

• The scene: a population of wild fruit flies minding its own business on several bunches of rotting bananas, cheerfully laying their eggs in the mushy fruit...

Disaster strikes:• A hurricane washes the bananas and the

immature fruit flies they contain out to sea. The banana bunch eventually washes up on an island off the coast of the mainland. and produce healthy offspring with the mainland flies. These flies begin to live a happy life on the island.

The populations diverge:• Ecological conditions are slightly different

on the island, and the island population evolves under different selective pressures and experiences different random events than the mainland population does.

So we meet again:• When another storm reintroduces the island

flies to the mainland, they will not readily mate with the mainland flies since they’ve evolved different courtship behaviors. The few that do mate with the mainland flies, produce inviable eggs because of other genetic differences between the two populations.

Modes of Speciation

• Geographical Isolation (allopatry) • Reduction of Gene Flow• Genetic Drift

– Bottlenecking– Founder effect

• Reproductive Isolation

Geographic Isolation• Scientists think that geographic isolation is a common

way for the process of speciation to begin: rivers change course, mountains rise, continents drift, organisms migrate, and what was once a continuous population is divided into two or more smaller populations.

• It doesn’t even need to be a physical barrier -it might just be unfavorable habitat between the two populations that keeps them from mating with one another.

Reduction of Gene Flow• speciation might also happen in a population

with no specific extrinsic barrier to gene flow. • a population extends over a broad geographic

range, and mating throughout the population is not random

• Individuals in the far west would have zero chance of mating with individuals in the far eastern end of the range.

Genetic Drift• In each generation, some individuals may, just

by chance, leave behind a few more descendents than other individuals. The genes of the next generation will be the genes of the “lucky” individuals, not necessarily the healthier or “better” individuals.

• However, this reduces the genetic variation of a species.

Bottlenecks• Population bottlenecks occur when a population’s size is reduced

for at least one generation. Because genetic drift acts more quickly to reduce genetic variation in small populations, undergoing a bottleneck can reduce a population’s genetic variation by a lot, even if the bottleneck doesn’t last for very many generations.

Founder effect• A founder effect occurs when a new

colony is started by a few members of the original population. This small population size means that the colony may have:– reduced genetic variation from the original

population. – a non-random sample of the genes in the

original population.

Reproductive Isolation

• Population increase in size to a point where their genetic material begins to differ and they can no longer reproduce.

• One group of frogs mates during the fall, and another similar species mates in the spring. Fall and spring species shall never mate… or will they?

Genetic Material Differs Mating times differ

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.