Evidence for Evolution

Fossils

Evidence for evolution

• Fossils

• Show: Evolution Primer: How do we know evolution happens?

Evidence for evolution

• DNA• All life uses the same 4 DNA bases: thymine,

adenine, guanine, cytosine• Biochemical pathways trace evolutionary

relationships just as fossils do

Evidence for evolution• Sense of smell• All mammals have many genes for smell—about 3

% of all their genes• In humans, that’s about 1,000 genes.– BUT 300 genes in humans are useless-DO NOT work– WHY?

• Whales, dolphins also have odor genes useful in air, but not water– BUT: NONE of the genes in whales and dolphins works.

Whale’s blowhole is used for breathing, not smelling.

Evidence for evolution

• Homology: characteristics that organisms share from a common ancestor

• Good example: limbs of tetrapods

Evidence for evolution

• Biogeography: the geographic distribution of species tells stories that geology and evolution can shed light on

• e.g.: Dinosaurs that can’t swim, but are found on several continents says those continents were once connected

The finches on the Galapagos are thought to have evolved from a single species of ancestral finch, probably the generic sort of seed-eating finch shown in the center. When a population of finches was reproductively isolated on one of the islands, it adapted over time to feed on a new food source. After time, it was sufficiently different from its ancestor to be considered a new species.

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Evidence for evolution• Artificial selection– Humans can mimic the selection process, bend

evolution to our will (sometimes!!) and produce useful plants and animals.

– Check out corn (teosinte)

Adaptations

• Traits that are successful in their environment• An adaptation to one environment may be

NEUTRAL or UNFAVORABLE in another environment

• May be simple—heavier coat in colder climate—or complex—the mammalian eye

Again:

• Adaptations are specific to the environment.– A zebra’s coat pattern is camouflage in the African

savannah. It would not be advantageous in a North American grassland.

– Running speed is advantageous for a cheetah on the savannah. But cats in the rainforest (e.g., jaguar) are not fast. Strength and stealth are more important than speed there.

Adaptation examples: mimicry

• How could such mimicry evolve?• What is the advantage to the

orchid?• Is there a cost or benefit to the

wasp?

• Some orchids (a kind of flower) mimic wasps. They look enough like a female wasp to fool males into ``mating’’ with them and thus transfer their pollen

Adaptation examples: more mimicry

• • Katydids have evolved a body form that looks like a leaf.

• Why? What is the advantage to the katydid?

Adaptation examples: still more mimicry

• • Non-poisonous king

snakes mimic poisonous coral snakes

• Many examples of mimicry in nature

Speciation

• One species evolves into another OR splits into two.

• How can this happen?– Geographic isolationallopatric speciation

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Biodivrsity patterns: hotspots

Birds in South America

History of life

• As previous picture shows:– Complex creatures and structures have evolved– But simple life forms still common and dominate

in many habitats ``Earth still belongs to the bacteria’’

– Speciation generates diversity; extinction reduces it

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Extinction

• The disappearance of a species from Earth• Local disappearance is called extirpation

• 99% of ALL species that have ever existed are extinct

Extinction• Two kinds:1. Background: the regular, consistent,

extinction of species over millions and hundreds of millions of years

- Result of environmental change, species interactions

2. Mass: the relatively sudden extinction of a great number of species in a short period of time (few million years, or less)

This graph shows extinction rates. You can see that five times in the last 600 million years, the rate has spiked up. Those are MASS EXTINCTIONS. The last one is when the dinosaurs died. Between mass extinctions, there is a more steady extinction rate, called BACKGROUND EXTINCTION.

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Date of extinctionmya=million years ago

% species lost Species affected

65 myaCretaceous

85 Dinosaurs, plants (except ferns and seed bearing plants), marine vertebrates and invertebrates. Most mammals, birds, turtles, crocodiles, lizards, snakes, and amphibians were unaffected.

213 Triassic 44 Marine vertebrates and invertebrates.248

248 Permian 75-95 Marine vertebrates and invertebrates.380

380 Devonian 70 Marine invertebrates

450-440Ordovician

50 Marine invertebrates

6th mass extinction?

• We are in the midst of a 6th mass extinction.• First one caused by human activity.