Principles of Evolution

5-23-16

Chapter 18 section 1

Announcements:

• Quiz 5 (last quiz!!!) is on Wednesday

– Topics: biotechnology (chapter 17.1) and principles of evolution (chapter 18.1)

Learning Goals for Today:

• Discuss the theory of evolution

• List some of the evidence that Darwin used to formulate the theory of evolution

• List some of the data used to support the theory of evolution

• Predict how a population may change over time

Evolution: what is it?

• Book definition of evolution:

– the change over time in the characteristics of a population

• A population consists of all the individuals of one species in one location

– Micro- : An increase in the frequency of the gene for dark wings in beetles from one generation to the next

– Macro- : The extinction of all dinosaurs

Pre-Darwin and Wallace:

• All organisms were created simultaneously (by a creator)

• They did not change

Greek philosophers:

• Plato (427–347 B.C.) each object on Earth is just a temporary reflection of its divinely inspired “ideal form”

• Aristotle (384–322 B.C.) increasing complexity of organisms indicates their perfection in the “Ladder of Nature”

Humans

Mammals

Birds

Reptiles and amphibians

Whales and porpoises

Fish

Squids and octopuses

Lobsters, crabs, etc.

Snails, clams, etc.

Insects, spiders, etc.

Jellyfishes, sponges, etc.

Higher plants

Lower plants

Inanimate matter

What got people thinking that organisms could change

• 18th century: world exploration revealed more species than anticipated

• Naturalists including Georges-Louis Leclerc noticed that each geographical location had its own group of species, even when environments were similar

• Some species in the same location were similar but different in some aspects

• Having different sets of species in the same location was inconsistent with the idea of fixed and unchanging forms

How could this change (evolution) happen?

• Jean Baptiste Lamarck (1744–1829) proposed inheritance of acquired characteristics – Due to use or disuse of different parts

• “use it or lose it”

– These modifications are passed to offspring

Theory unsupported for genetic inheritance

Is supported for cultural/behavioral characteristics

Dude,

step off!!

According to Lamarck

• Mid 1800s – Explanations for the concept of evolution

• Both did expeditions in the tropics

• Charles Darwin (1831 to 1836, S. America, Australia, and Africa)

• Alfred Wallace (Brazil, 1848 to 1852; Malay Archipelago, 1854 to 1862)

Modern Perspectives

Published 28 years after the expedition in The Beagle began

Voyage of the H.M.S. Beagle and Darwin

Voyages of Wallace and Darwin

Australia America Darwin (and Wallace) noticed:

Similar organisms on different continents

Found in similar environments

Appear to have similar roles

Darwin’s Finches, Residents of the Galápagos Islands

Beak size corresponds with food preference

Idea: changes in food supply leads to selection for or against specific beak shapes

For example, seed-eating finches had stronger, thicker beaks for breaking seeds, and insect-eating finches had spear-like beaks for stabbing their prey.

Darwin noticed that different, yet related, animal species often occupied different habitats within a local area.

Armadillo Glyptodon

Darwin notices fossil organisms that resembled modern organisms

Darwin noticed that species were changing

• Darwin wanted to explain the biological diversity he observed in a scientific way

• As he traveled, Darwin noticed three distinctive patterns of biological diversity: (1) Species vary globally, (2) species vary locally, and (3) species vary over time.

Idea of natural selection

• Exploration of new lands revealed a staggering diversity of life – Discovered vast numbers of new species

– Early explorers often took naturalists along to catalogue the plant and animal life they found

• Darwin: naturalist on the Beagle

• Wallace was a naturalist too but he worked independently

– Idea of “survival of the fittest” explains changes in populations

Natural selection

• Successful reproduction of individuals with favorable traits that survive environmental change because of those traits

• Leads to evolutionary change

• Fit = has more babies that survive

How Does Natural Selection Work?

• Darwin (and Wallace) proposed that life’s diverse forms arose through the process of descent with modification (evolution)

– Individuals in each generation differ slightly from the members of the preceding generation

– Over long time periods, small differences accumulate to produce major transformations

LaMarckian and Darwinian views

Four postulates of evolution –Variation in phenotype

• Postulate 1: Individual members of a population differ from one another

Fig. 14-6

• Postulate 2: phenotypic differences can be passed on from parents to offspring – must be heritable

Phenotypes must be heritable

More offspring are produced than are able to survive

• Postulate 3: In each generation, some individuals in a population survive and reproduce successfully but others do not

• Postulate 4: Individuals with advantageous traits (phenotypes) survive and leave the most offspring, process known as natural selection

Survival of the fittest because of natural selection

What is natural selection?

• Unequal survival and reproduction of organisms with different phenotypes, caused by environmental forces

Natural selection modifies populations over time

• Natural selection acts on individuals within a population; however, it is the population that changes over time

– Over generations, the population changes, as the percentage of individuals inheriting favorable traits increases

Adaptation

• A heritable trait that helps the survival and reproduction of an organism in its present environment

– The webbed feet of platypuses are an adaptation for swimming

– The snow leopards’ thick fur is an adaptation for living in the cold

– The cheetahs’ fast speed is an adaptation for catching prey

How does natural selection happen: step by step?

• A population with genetic/phenotypic variation

1. A change occurs in the environment

2. Well-adapted individuals leave more offspring than do poorly-adapted individuals

3. Genetic frequencies within the population change

How Natural Selection Works

How Natural Selection Does Not Work

• Adaptation has nothing to do with effort

• Natural selection does not give organisms what

they “need”

• An advantage must be heritable in order for it

to be passed on to offspring

Worksheet on natural selection

Support for the Process of Evolution

• Fossils provide evidence of evolutionary change over time

• Comparative anatomy gives evidence of descent with modification

• Embryological similarity suggests common ancestry

• Modern biochemical and genetic analyses reveal relatedness among diverse organisms

Modern whales

0

40

45

50

Basilosaurus

Dorudon

Rhodocetus

Ambulocetus

Pakicetus

Mill

ion

s o

f ye

ars

ag

oFossils Provide Evidence for Whale

Evolution from Land Mammals

Fig. 14-7

The Evidence for Natural Selection

• Fossil record

• Transitional fossilsCaudipteryx – 125 mya

Reptiles birds

Archaeopteryx – 145 mya

The Evidence for Natural Selection

• Fossil record

• Transitional fossils

Tiktaalik – 375 mya

Water land animals

Lobed-finned fish

salamander

The Evidence for Natural Selection

• Fossil record

• Transitional fossils

Modern toothed whales

Rodhocetus swam withan up-and-down motion. 47 mya

Ambulocetus probably walked on land. 49 mya

Pakicetus attocki lived on land. 55 mya

Land back to sea

Divergent evolution

• Sometimes, evolution gives rise to groups of organisms that become tremendously different from each other

• When two species evolve in diverse directions from a common point, it is called divergent evolution

Comparative anatomy (homologous structures) is a result of divergent evolution and provides

support for common ancestry

Pterodactyl

Bird

Bat

Dolphin

Seal

Dog

Sheep Shrew

humerus

ulna

metacarpals

phalanges

radius

carpals

Human

GRASPINGRUNNINGSWIMMINGFLYING

Bones in the appendages share the same overall construction

Vestigial Structures: evidence of loss of once important structures (divergent evolution),

“evolutionary baggage”

These vestigial bones are similar in

structure to those of the salamander

but serve no function; all three animals

inherited the bones from a common

ancestor

The bones of a salamander’s hindlimb

function in support and locomotion

(c) Boa constrictor

(b) Baleen whale

(a) Salamander

Shrunken to the point that they no longer constitute a survival-reducing burden.

The Evidence for Natural Selection

• Comparative anatomy

• Vestigial structures – relics of the past

The Evidence for Natural Selection

• Pseudogenes• “Dead” genes

• Products of divergent evolution

• Example: Ascorbic acid (vitamin C) synthesis

Convergent Evolution gives rise to analogous structures

• Similar traits (“analogous structures”) evolve separately, but in similar environments

• Similar selection pressures

• Example: Placental mammals vs marsupials

Wolf

Thylacine

Flying squirrel

Flying phalanger

Niche Burrower

Mole

Lesser anteater Ring-tailed lemur Ocelot

Spotted cuscus

Numbat

Marsupial mole

Anteater Climber Glider

Marsupial

mouse

Australian

Marsupials

Placental

Mammals

Nocturnal

Insectivore

Grasshopper

mouse

Stalking

Predator

Chasing

Predator

Tasmanian

quoll

Convergent Evolution

North America

Asia & Australia

CactusEuphorbia

Analogous Structures: similar function but unrelated, product of convergent evolution

Fig. 14-10

All vertebrate embryos look similar –homologous traits in embryos provide

evidence of a common ancestor

At one point all possess gill slits and a tailWhich is the lemur, pig, human?

Lemur pig human

Homologous biochemical and cellular features - Evidence for common ancestry

• Shared features of all cells

– DNA as a genetic blueprint

– RNA, ribosomes, and approximately the same genetic code for translation

– same set of 20 amino acids to build proteins

– ATP to transfer energy

humanmouse

humanmouse

humanmouse

humanmouse

humanmouse

humanmouse

humanmouse

humanmouse

Cytochrome c gene is highly conserved between species

Natural Selection - conclusions

• Natural selection is not random

• Traits are produced by chance

mutations

• The traits that persist in a

population are those that

work best in the organism’s

environment