Evolution

The unifying theme of biology is

1. A) taxonomy. 2. B) genetics. 3. C) ecology. 4. D) evolution. 5. E) None of the choices are correct.

Figure 13.00b

Figure 13.00c

Figure 13.00d

Evolution

Evolution means change over time

Outline

• Overview of evolution & natural history• Darwin’s voyage• Evidence for evolution• Natural selection• Population Genetics• Hardy-Weinberg Equilibrium• Microevolution

The Earth today is not what it once was

• The earth is thought to be 4.5 billion years old

• Life is thought to have appeared ~3.8 billion years ago

• The early atmosphere had methane, carbon monoxide, and

• Essentially no oxygen

Molecules common to all living things formed on a hot earth which lacked oxygen in its atmosphere

Stanley Miller took early earth ingredients and treated with “lightning” Results- Amino acids; nucleic acids

The past contains species very diffent from familiar species of today

• Species of the past are radically different from what exists on earth today

• Converse is true- things that exist today are not seen in the past

• The Burgess Shale shows the rapid increase in diversity from the Cambrian explosion, ~530 M.y.a.

Yet there are connections between species of past and present

• Species of today have physical similarities

• This archaeopteryx fossil shows feathers

People did not always know the earth was ancient

• Anglican archbishop James Ussher, 1581-1656

• October 23, 4004BC: Earth was created

Extinction was once only a theory

• Mary Anning, fossil hunter, found a plesiosaur in 1821• Other marine fossils were found several miles from

shore• This and other evidence caused speculation about the

age of the earth

The Geologist Charles Lyell proposed that the earth was much, much older

• Posited the idea that continents have moved over time

• This is continental drift, caused by plate tectonics

• Continents move very slowly

• Earth must be very old• Darwin carried Lyell’s

book, Principles of Geology (1833), with him on the Beagle

About 250mya, all continents were joined

• Contients had drifted together

• Continents subequently drifted apart

Continents can collide to form mountains

• This raises aquatic sediments from ocean bottoms

Charles Darwin became curious about how species came about

• February 12, 1809- April 19, 1882

• Flunked out of med school• Didn’t much like Divinity

school, either• Became a naturalist aboard

the HMS Beagle• Darwin lived in a time when

science, industry, and society were beginning to progress more rapidly

The Voyage of the Beagle

Darwin’s critical observations were comparisons between island species and

mainland species

Marine Iguana and South American Iguana

Flightless cormorants live only on the Galapagos

A Variety of Finches are found in the Galapagos

Finches each have adaptations for different small island environments

They have many other traits in common

Darwin’s inference: The finches have a single common ancestor

Likewise, the marine iguanas must have come from the mainland

Evolution- the change in species over time

• New species are formed from older ancestors

• Some become extinct, others evolve into different species

But what was the mechanism?

• How did a species change over time?

• Lamarch proposed a mechanism:

-By repeated strain, a giraffe acquires a long neck

-The long neck is inherited by the offspring

Natural Selection

The mechanism by which life evolves

Darwin’s Mechanism: Natural selection

• Those best suited for their environment are selected for survival

• Genes are inherited by the next generation

• Better-adapted species pass on genes suited for the environment

• Next generation is better suited for environment than previous generation

The parts of Darwin’s theory

• 1. Overproduction• 2. Variation of individuals• 3. Differential reproductive success

1. Overproduction

• Living things tend to produce more offspring than are able to survive

2. Individual Variation

• Individuals in a species are different from each other

• Some are better adapted to their environment than others

• Where does the variation ultimately come from?

Mutations are the source of all genetic variaton

• Mutations- Changes in DNA of an organism

• Mutations can be caused by mutagens

• UV radiation, toxins, etc.• Also come from errors in

DNA replication• Also from errors in

crossing over• And meiosis, etc.

3. Differential Reproductive Success

• Those that are better adapted to their environment are more likely to survive

• Those that survive will pass their genes to their offspring

• Populations evolve, not individuals

As a result, populations

change • Population is better

adapted for survival in its environment

In this way, the population changes- microevolution

When populations of a species become isolated, they evolve independently, causing speciation

• The isthmus of Panama only formed ~3mya

• Its formation isolated shrimp species into Caribbean and Pacific populations

• Now they are separate species

Given more time, microevolution results

in macroevolution

• Many speciation events over many millions of years leads to great changes

• Fossils from Pakistan and India have elucidated the evolution of the whale

By this principle, all life evolved from a common ancestor

More recently, humans and apes evolved from a common ancestor

Primarily because of this, many people didn’t like Darwin’s theory

• One consequence of the theory is that all living things have a common ancestor

• Humans did not descend from chimpanzees- but they do share a common ancestor

Consequences of Natural Selection

• Some insects can tolerate pesticide

• Survivors pass resistance genes to the next generation

• Do these genes exist before the crops are sprayed?

• What other examples are there of this?

What can be said about these insects?

Consequences of Natural Selection

• Some insects can tolerate pesticide

• Survivors pass resistance genes to the next generation

• Do these genes exist before the crops are sprayed?

• What other examples are there of this?

Evidence for evolution

• Fossil evidence• Biogeography• Comparative anatomy • Comparative embryology• Molecular biology

Which of the following is a orrectly written scientific name?

• A) Australopithecus afarensis • B) homo sapiens • C) musca domesticus • D) Acer pennsylvanicus

Layers of sediment fall upon dead organisms, ultimately forming fossils,

creating the fossil record

Looking down layers is looking back in time

• The principle of superposition

• The layers of the grand canyon go back over 600 million years

Fossil Evidence shows variant species in different layers

Which of these creatures would be least likely to be successfully fossilized?

• A) Turtle • B) Rose flower • C) Rhinoceros • D) Clam

Biogeography

• Marsupials are not better adapted to Australia

• Invasive placental mammals are driving many marsupials to extinction

Comparative anatomy

• Similar structures exist in dissimilar animals, serving dissimilar functions

• Homologous structures suggest a common ancestry

Vestigial Structures suggest terrestrial ancestry in whales

Comparative embryology

Evidence from Molecular Biology

• Similar animals have similar DNA sequences

• Less similarity of species= less similarity of DNA

Other ways a population can evolve without natural selection

Genetic DriftThe bottleneck effect

The founder effect

Genetic Drift- the change in allele frequencies in a population or species over time by chance

Figure 13.23

Population bottlenecks magnify the effects of luck

Consequences of a bottleneck

• Cheetahs have very low genetic variation

• How can a bottleneck reduce diversity in a population?

A population retains the genes of its founder(s)

Special kinds of selection

• Sexual selection• Artificial selection

Sexual Selection• Competition within sexes

is a major source of differential reproductive success

• Males compete, or females select

• Sexual selection leads to sexual dimorphism

• “The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me feel sick”- Charles Darwin

Pair bonding is greater in species which are less dimorphic

• What about humans?• Are humans a

tournament species, or are a pair-bonding species?

• How can you tell?

Artificial selection shows the pliancy of species morphology

Human Evolution

Humans have several adaptations which distinguish us from relatives

• Pelvis for bipedal walking

• Opposable thumbs, but not toes

• Larger braincase

• Humans did NOT evolve from chimps- but the share a common ancestor

Scarcity of fossils makes tracing human history difficult

• Hominin fossils are numbered in the dozens

Humans have their roots in Africa

• Primates evolved in• While evidence of

Hominin ancestors can be found in Asia, true modern humans are believed to have come from Africa ~200-100kya, with migrations beginning ~60kya

Homo neanderthalis is thought to be an extinct subspecies

• Found primarily in Europe• Arrived in Europe ~350kya,

extinct by ~30kya• Adapted for cold• Wiped out by H. sapiens?• Did they crossbreed with

modern H. sapiens?• mtDNA evidence suggests

they did not

Which of the following refers to the ability of early hominids to

walk on two feet?• A) Bipedalism • B) Digitigrade • C) Plantigrade • D) Tetrapedal