Chapter 22: Descent with Modification Your wonderful instructors: Zakk Drumm Ryan O’Kane Torpey White.

Chapter 22: Descent with ModificationYour wonderful instructors:Zakk DrummRyan O’KaneTorpey White

22.1- Pre Darwin Before the 1700s, most of Western Civilization believed

in the theories of Aristotle He claimed, through observation of nature, that all life

was perfectly suited for its place and nature and always had been- species were a fixed constant.

This fit in with creationism, leading to its wide acceptance in the European world.

Progress Carolus Linnaeus (1707-1778) was a Swedish physician

who created the classification system widely adopted in the biological field.

While meant to create order and better define creation, this theory ended up being used as evidence against creationism and for evolution.

Progress Continues Fossils: the remains or traces of organisms from the

past. Found in old rock strata, fossilized remains of species

that never existed were found by many in the field of Paleontology.

Paleontology: The study of fossils that was largely developed by Frenchman George Curvier (1769-1832)

Curvier was an idiot. Catastrophism: The principle that events in the past

occurred suddenly and were caused by mechanisms different from those operating in the present.

It was a catastrophe aaw yeah that Curvier failed to see the link between ancient species and similar ones around today, rejecting evolution while looking at its key piece of evidence.

Progress Finally, someone with a brain! James Hutton was a Scottish geologist who saw that the

Earth’s current features could be explained through looking at relatively constant geologic forces that occur gradually

Charles Lyell (1797-1875), the leading geologist of Darwin’s time, made these ideas into the theory called uniformitarianism.

Darwin got many of his ideas from Lyell and Hutton’s work.

Evolution 1.0 French biologist Jean-Babtiste de Lamarck (Call him

‘Tiste)(1744-1829) was the first to put forth an idea about the nature of evolution

This was the first, despite the fact that many already believed in ideas similar to evolution

While he was a visionary for seeing and putting forth an idea on evolution, is widely known for his idea’s utter failure.

‘Tiste’s theory Lamarck’s proposition was based off two false ideas. First- use and disuse. Suggests that tissues used become

reinforced while those which are not atrophy and decay. Second- Inheritance of acquired traits. This idea of

inheritance was revolutionarily, but was flawed in order to explain how the first part of his idea made sense.

He believed that evolution occurred because organisms have an innate drive to become more complex.

Was vilified for proposing evolution. Poor ‘Tiste.

22.2: Evolution 2.0 Charles Darwin (1809-1882) was born in England. His father wanted him to go to medical school, but he

got bored so he became a clergyman. Went to Cambridge, where he became John Henslow’s

protégé. Henslow was a botanist and, once Darwin graduated, scored him a sweet deal to talk to a captain for months on end, traveling around the world sea by boring sea.

The Beagle what a cute dog

On the Beagle, Darwin read Lyell’s Principles of Geology.

Earthquake Noticed fossils of sea creatures high in mountains This reinforced what Lyell taught, shook the notion that

the Earth was just thousands of years old. His interest in the geological distribution was furthered

when he came into contact with Galapagos species that differed from those on the mainland.

Darwin focused his ideas of evolution on adaptions that organisms possessed.

Adaptions: characteristics of organisms that enhance their survival and reproduction in specific environments.

Speculated that adaptions came as the result of natural selection.

That will be discussed later.

Competition In the 1840’s, Darwin summarized his ideas and theories and told

Lyell about them by the mid 50s. Lyell was skeptical, but encouraged Darwin to publish before

someone else did. Darwin probably did not want to, after noting what happened to

Lamarck. He continued to gather evidence and refine his ideas. In 1858, Wallace (1823-1913) sent Darwin his thoughts on

evolution, and published a paper on it. After he read Darwin’s book on evolution, which Darwin finished

shortly after, he thought Darwin should get credit. What a nice guy.

The Origin of Species The book Darwin published contained two main ideas. Firstly, Descent with Modification. Darwin used Linnaeus’s classification system to show

how similar animals also had similar adaptions. Put forth the time-tested idea of artificial selection to

compare to natural selection and adaptions. The similarities convinced many.

2nd main point: Natural Selection Its important to know- take notes! 1. Natural selection is a process in which individuals that have

certain heritable characteristics survive and reproduce at a higher rate than other individuals.

2. Over time, natural selection can increase the match between organisms and their environment.

3. If an environment changes, or if individuals move to an new environment, natural selection may result in an adaption to these new conditions over time- this may give rise a new species.

Important to note- traits must be heritable and individuals cannot evolve; only applies to populations.

22.3 There is much proof that supports the notion of

evolution. One easy example of this is how HIV can quickly

become drug resistant Shows both descent with modification and artificial

selection. Quick, Aiswarya, explain how!

The Fossil Record Looking at fossils , scientists were able to postulate

how the current state of the world came to being The fossil record showed how aquatic organisms slowly

developed into land animals Fossil record is, however, incomplete Not enough evidence to show how cetacean limb

structures evolved over time.

Homology Homology: Similarities resulting from common ancestry is

known as homology. Homologous Structures: underlying structures in the

physiology of different organisms that indicate common ancestry

Vestigial Structures: Key evidence for evolution in that they are structure not used by an organism, but were used by their evolutionary ancestors.

Evolutionary tree: a diagram that reflects evolutionary relationships among groups of organisms.

More evidence Convergent Evolution: the independent evolution of

similar features in different lineages. Analogous Structures: resemblance in features due

to convergent evolution.

Biogeography Biogeography: the geographic distribution of species. Continental Drift: the slow movement of Earth’s

continents over time. Pangaea: The one supercontinent which existed 250

million years

Torpey your stupid powerpoint doesn’t work, pull it out now.

Chapter 24: The Origin of Species

Overview Speciation – the process by which one species splits

into two or more Responsible for the diversity of life Can be caused by a single gene

Microevolution – changes over time in allele frequencies in a population

Macroevolution – the pattern of evolution over long time spans

The Definition of Species Primary definition: the biological species concept

A species is a group of populations whose members have the potential to interbreed in nature and produce viable, fertile offspring

Other definitions include: Morphological species concept – characterizes species by

structural features Ecological species concept – characterizes species by its niche Phylogenetic species concept – defines a species as the

smallest group of individuals that share a common ancestor

Reproductive Isolation Reproductive isolation – the existence of biological

factors that impede members of two species from producing viable, fertile offspring

Classified as either prezygotic or postzygotic barriers

Prezygotic Barriers Blocks fertilization from occurring Habitat isolation – species live in different habitats Temporal Isolation – species breed during different

hours/seasons Behavioral Isolation – different courtship rituals Mechanical Isolation – mating is attempted, but not

completed Gametic Isolation – the sperm can’t fertilize the egg

Postzygotic Barriers Takes place after fertilization Reduced hybrid viability – the hybrid does not develop

correctly or survive easily in the environment Reduced hybrid fertility – hybrids can be sterile Hybrid breakdown – first generation hybrid is viable

and fertile, but the next generation is not

Allopatric Speciation Gene flow is interrupted by geographic isolation Genetic drift, natural selection, and mutations in

subpopulations can lead to speciation

Sympatric Speciation Occurs in populations that live in the same area Can be brought about by

Polyploidy Habitat differentiation Sexual selection

Polyploidy Accidents in cell division Polyploidy – extra sets of chromosomes, two forms

Autopolyploid – more than two chromosome sets from a single species, reproductively isolated form parent species Triploids have reduced fertility, but tetraploids can produce

tetraploid offspring by self-pollination or mating with another tetraploid

Allopolyploid – sterile hybrid that reproduces asexually can become fertile Can only mate with other allopolyploids, not parent species

Habitat Differentiation and Sexual Selection Habitat differentiation - A subpopulation exploits a

habitat or resource not used by others North American apple maggot fly split from original

population and began eating apples, there is now temporal isolation between the two species

Sexual selection – preference in mates can lead to long term changes Pundamilia pundamilia females breed with blue-tinged

backs while Pundamilia nyererei breed with red-tinged backs

Hybrid Zones A region in which members of different species meet

and mate, producing hybrids Pattern of the hybrid zone dependent on fitness of

parent and hybrid species

Hybrid Zones over Time Reinforcement – the reinforcement of reproductive

barriers, occurs when hybrids are less fit than parents Fusion – reproductive barriers are weakened until the

parent species fuse into a single species, occurs when hybrids are more fit than parents

Stability – hybrids are formed, but reproductive barriers are neither strengthened nor weakened

Punctuated Equilibria Periods in the fossil records where sudden changes

occur Can occur if changes occur rapidly (geologically speaking)

in the species’ life Once speciation begins, it can be completed quickly

Other species change gradually over time

Essays! Describe the modern theory of evolution and discuss how it is supported by

evidence from two of the following areas. population genetics molecular biology comparative anatomy and embryology

Do the following with reference to the Hardy-Weinberg model. Indicate the conditions under which allelic frequencies (p and q) remain constant from

one generation to the next. Calculate, showing all work, the frequencies of the alleles and the frequencies of the

genotypes in a population of 100,000 rabbits, of which 25,000 are white and 75,000 are agouti. (In rabbits the white color is due to a recessive allele, w, and the agouti is due to a dominant all, W.)

If the homozygous dominant condition were to become lethal, what would happen to the allelic and genotypic frequencies in the rabbit population after two generations?

Essay Q with Darwin Darwin made 4 key observations about the nature of life. 1. Members of a population often vary greatly in their traits 2. Traits are inherited from parents to offspring 3. All species are capable of producing more offspring than their

environment can support. 4. Owing to lack of food or resources, those offspring don’t survive.

From these observations, try and make the same inferences about evolution that Darwin did. If unable, try and make 2 logical inferences just for fun.

See when done- Chapter 22 page 458.