evolution by natural selection. evolution §evolution - change in the gene pool of a population over...
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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 Skull at Museum of Man in CA