evolution by natural selection. evolution §evolution - change in the gene pool of a population over...

Evolution

By Natural Selection

EVOLUTIONEvolution - change in the gene

pool of a population over timeOrganisms change over time –

this is observable fact. How organisms have changed throughout earth’s history has resulted in a number of scientific and non-scientific theories.

What is a scientific theory?

Theory - a major hypothesis that has withstood the test of time• Based on observations and evidence

• The closest to a complete explanation that science can offer

• 40 second evolution• Homer Simpson Evolution

Theory of Natural SelectionBiology’s best explanation of how

populations change over time is called the Theory of Natural Selection.

It was proposed in 1859 by Charles Darwin and has stood, with minor corrections, for over 150 years.

It is one of the cornerstone theories of modern biology.

Charles Darwin in 1859, the year The Origin of Species was published

CHARLES DARWIN

Charles Darwin – an Englishman credited for first describing natural selection• HMS Beagle – a British survey ship on which Darwin was a naturalist. This ship sailed around the world in 1831.

Section 15-1

Figure 15–1 Darwin’s Voyage

Galapagos Islands – located 600 miles west of South America. The islands have very different climates and thus the organisms adapt according to the environment. Giant tortoise, marine iguanas, and finches vary from island to island due to different environments

Pinta IslandIntermediate shell

Pinta

Isabela IslandDome-shaped shell

Hood IslandSaddle-backed shellHoodFloreana

Santa Fe

Santa Cruz

James

Marchena

Fernandina

Isabela

Tower

Giant Tortoises of the Galápagos Islands

A Galápagos Islands tortoise

Artificial Selection – people chose particular species to breed (selective breeding) Artificial selection helped to explain that variations in species could make them better adapted.

Dog breeders, farmers, gardeners have been using artificial selection for years.

Golden Doodle

Cockapoo

Himilayan

Golden retriever and poodle

Cocker spaniel and poodle

Persian and Siamese

Tangelo = madarin orange and grapefruit

Broccoliflower = broccoli and cauliflower

Artificial selection: diverse vegetables derived from wild mustard

Natural Selection – when the biotic and abiotic conditions of the environment an organism lives in influences which individuals survive to reproduce.

Principles of Natural Selection

1. Genetic variation within the population

2. Overproduction of offspring3. Constant struggle to survive4. Those with the best adaptations

survive and pass their genes on to the next generation.

1. Genetic Variation Within the Population

2. Overproduction of Offspring

3. Constant Struggle to Survive

4. Those with the Best Adaptations Survive and Pass Their Genes on to the Next Generation

Explaining Evolution

The theory of Natural Selection is overwhelmingly supported by data gathered from the following areas of science:

Supporting Evidence

FossilsComparative anatomyEmbryologyBiochemistryGeneticsDirect observation

FOSSILS

Fossils - a trace of an organism that lived long ago

Fossil records- use radiometric dating or rock layers to date fossils

Fossil records are incomplete:• soft tissues• weather

Geographic distribution of species Similar organisms in different areas

Fossils of extinct organisms

COMPARATIVE ANATOMYComparative anatomy- The

study of structures of different organisms

Homologous structures - similar structures modified between different organisms

• The more similar the structures, the closer the relationship between two organisms

• Example: a bat’s wing, a horse’s leg and a human forearm

Homologous structures

Vestigial Organs - structures that have no function in present organisms, but may have been used in ancestors Example in animals

• pelvic bone in some snakes and whales

Examples of vestigial organs in humans • appendix• wisdom teeth• body hair• pointed canines

EMBRYOLOGY

Comparative embryology - the study of embryos (early stages of life) of different organisms The more similar the embryos, the more closely related two organism are

• ex. human and pig embryos appear very similar to each other

BIOCHEMISTRY & GENETICS

Chemicals (like proteins, DNA, mRNA etc) in different organisms show similarities.

More similar chemicals means more closely related

Example- Hemoglobin in chimpanzees is very similar to hemoglobin in humans

GENETICSHow are offspring genetically

different from their parents? In other words, how can evolution occur from one generation to the next? Meiosis – remember, individuals

can make lots of genetically different sex cells

Mutations – DNA can change! Sex – combines two individuals’

DNA together

DNA sequences of all living things have many similarities

Base sequences of DNA• DNA of humans and chimpanzees is 98% identical

• DNA of humans and other mammals is 80% identical

Hemoglobin sequences in vertebrates

DIRECT OBSERVATION

Direct observation - evolutionary changes are happening NOW• Example - bacteria becoming resistant to antibiotics

How Evolution Works

TYPES OF SELECTION

Some vocab…

Gene Pool - the entire collection of genes among a population

Population - All organisms within a breeding group (same species)

Gene Frequency - The number of times an allele appears in a gene pool

Sample Population

48% heterozygous

black

36% homozygous

brown

16% homozygous

black

Frequency of Alleles

allele for brown fur

allele for black fur

Figure 16–2: Relative Frequencies of Alleles

Changes in gene frequency mean that the population has evolved.

An entire population evolves, not an individual!

A specific gene may be “selected” for by the environment.

GENETIC DRIFTGenetic Drift - rapid changes in

gene frequency of a small, isolated population. Not the result of Nat.Sel. Example: in small populations, a recessive allele can become much more common

In the Amish population, certain genetic disorders are more common than in the general population.

Sample of Original Population

Founding Population A

Founding Population B

Descendants

Genetic Drift

Sample of Original Population

Founding Population A

Founding Population B

Descendants

Genetic Drift

OCEANIC ANGLER FISHSexual dimorphism

The deep sea angler shows a very strange sexual dimorphism. The male is very small and attaches itself to the

body of the female. The teeth and the jaw recedes and the blood circulation of the two animals become one. The male

spends the rest of his life attached to the female.

ADAPTATIONS

Adaptations - traits of a living organism that help it to survive in its environment

Adaptations first appear by chance!

TYPES OF ADAPTATIONSStructural – physical parts

• Ex. woodpecker’s tongue, anglerfish, anteater’s snout, hummingbird’s beak

Physiological – chemicals made by organism• Ex. poison venom of a snake, ink

of a squidBehavioral

Ex. migration of birds, mating dances

Buffalo Bill Dam on the Shoshoni River at Cody,

Wyoming and those dots are bighorns WALKING

ACROSS IT.

TYPES OF EVOLUTIONConvergent Evolution – when species

that are not closely related evolve similar traits (two species look like they are closely related and they are not)• Example: dolphins (mammals) and sharks

(fish)Divergent Evolution – one species

evolves into two or more species with different characteristics Example: lions and tigers evolved from a

common ancestor

Liger

SpeciationSpeciation –evolution of two different

species from one common ancestor.What keeps two species apart so that

they evolve differently? Isolating Mechanisms – keep groups

apart Geographic Isolation – geologic

changes occur that isolate individuals of a population

–Ex. Squirrels separated by Grand Canyon and Darwin’s finches separated by being on different islands

Squirrels in the Grand Canyon

NORTH AMERICA

Muskrat

Capybara SOUTH AMERICA

Coypu

Figure 15–14: Geographic Distribution

of Living Species

Beaver

Muskrat

Beaver andMuskrat

Coypu

Capybara

Coypu andCapybara

Genetic Isolation – genes don’t mix right

–Donkeys and horses make mules, but mules are sterile.

Temporal isolation – timings off–Different species of skunks that mate at different times of the year.

Behavioral isolation – behaviors don’t match

–Certain species of lightning bugs use different blinking patterns to attract mates.

A male bower bird builds a “bower” to attract mates.

• Blue footed boobies doing their mating dance

• Birds of Paradise doing their mating dance

• Many different mating scenarios

Tree of Life

FIRST ORGANISMSProkaryotes [bacteria] - first cells; have

genetic material (RNA or DNA); starting 3.5 bya

First prokaryotes were heterotrophs (eat food)

Some prokaryotes were Archaea, which include “extremophiles”

Later, some became autotrophs (make own food) Chemosynthesis - using energy from

chemicals to make food

Photosynthesis - using CO2 and light to make food• Cyanobacteria put oxygen into atmosphere.

• Oxygen drove some life forms to extinction, while other life forms evolved new ways to use oxygen (aerobic respiration).

• Oxygen formed ozone layer- shielded earth from harmful UV and allowed an explosion of life (2.7 bya)

A painting of early Earth showing volcanic activity and photosynthetic

prokaryotes in dense mats

Other big steps…Eukaryotes (cells with nuclei) about 2.2

byaPlants and animals begin in waterMulticellular organisms and sexual

reproduction in plants and animals (aquatic life) Increased genetic diversity

Plants and later animals colonize land around 450 mya.

First dinosaurs and then first mammals (245 mya)

Dinosaurs go extinct around 65 mya and this allows for evolution of larger mammals.

Extinctions are often followed by explosions of new life forms!

Remember your eras: Precambrium. Paleozoic, Mesozoic, and Cenozoic.

HUMAN EVOLUTIONDid man come from Monkey?

NO!Humans and monkeys evolved from

a common ancestor that lived approximately 65 million years ago and was a tree dweller (roughly the size of a cat). This was not a monkey like the monkeys today.

Modern GorillaModern Human

Comparing Human and Gorilla Skeletons

Modern Human Modern Gorilla

Skull atopS-shaped spine

Spinal cord exitsat bottom of skull

Arms shorter thanlegs; hands do not touch groundduring walking

Pelvis is bowl-shaped

Thigh bones angledinward, directlybelow body

Skull atopC-shaped spine

Spinal cord exitsnear back of skull

Arms longer thanlegs; hands touch ground during walking

Pelvis is longand narrow

Thigh bones angledaway from pelvis

Figure 32–16: Human and Gorilla Skeletons

HOMINIDSHominid family includes modern

humans and many distinctly different extinct species (we will look at one early hominid)

Bipedal – two-foot locomotion Freed hands to use tools

Opposable thumb – allowed hand to grasp objects and tools

Increased brain size Family that walks on all four

Australopithecus afarensis Homo erectus

Neanderthal Cro-Magnon Modern Homo sapiens

Large braincase

Large browridge

Large nose

Face protrudesforward

Large canineteeth

Weak browridge

Inflatedcheeks

Largenose

Strong chin

Even teeth

Round, highskull

Comparison of Skulls of Human Ancestors

Australopithecus afarensis

Fossils found only in N. AfricaVery small brain capacity~3.9-3.0 million years ago

(mya)“Lucy” (one of most famous)Bipedal apes that spent some

time in treesShort (Lucy is 1m)

Reconstructed parts in white

Reconstructed Skull at Museum of Man in CA