Introduction to Evolution: Darwin

Evolution Controversy: 1800’s Beliefs at the time: Earth is just a few thousand years old Earth is populated by forms of life have been here, unchanged,

since the beginning Many scientists engaged in study Lyell stated that geologic processes have shaped the planet

and are ongoing “the present is key to the past” Lamarck proposed “acquired traits”, did believe in evolution,

did not believe in extinction Cuvier studied fossils, firmly established extinction occurs,

did not believe in evolution

Charles Darwin His theory of evolution as expressed in The Origin of Species (1859): Earth is more than a few thousand years old Earth is populated by forms of life that change over time. Some life forms become extinct In more than 150 years, there is no evidence that disproves his theory

Mechanism of Evolution

Natural Selection

Evolution Evolution: A change in the gene pool of a population Gene pool: The total group of genes in a population.

Mechanism of Evolution Principles of Natural Selection 1. Within any population, there is genetic diversity.

Mechanism of Evolution Principles of Natural Selection 2. All populations live in an environment in which they compete for resources. 3. In their environment, some individuals have a better ability to survive and reproduce than other

individuals. 4. Those individuals that survive and reproduce pass on their more

successful traits to the next generation. The less successful individuals do

not pass on their traits because they don’t survive.

The environment selects the most fit organisms (“survival of thefittest”)

This is called natural selection.

Natural Selection If the environment changes, the individuals that can survive and

reproduce may change. Example: English peppered moth

Current Evolutionary Events There are contemporary examples of evolution as well

Antibiotic-resistant strains of bacteria Herbicide-resistant varieties of plants Pesticide-resistant varieties of insects

Artificial Selection Artificial selection: The process

by which species are modified by humans.

Plants and animals are chosen with the desired goal of producing offspring with specific traits.

Traits are “successful” if they are chosen by humans to be passed on to the next generation

Examples include all domesticated animals (horses, dogs, cats, etc.)

Another example: wild mustard

Artificial selectionTerminalbud

Lateralbuds

Brussels sproutsCabbage

Flowercluster Leaves

Cauliflower

Flowerandstems

Broccoli Wild mustard Kohlrabi

Stem

Kale

Speciation Over long periods of time, natural selection can give rise to new

species. Adaptive radiation occurs when many new species arise from a

single common ancestor Example: Galápagos finches

Beak variation in Galápagos finches

(a) Cactus eater. The long,sharp beak of the cactusground finch (Geospizascandens) helps it tearand eat cactus flowersand pulp.

(c) Seed eater. The large groundfinch (Geospiza magnirostris)has a large beak adapted forcracking seeds that fall fromplants to the ground.

(b) Insect eater. The green warbler finch (Certhidea olivacea) uses itsnarrow, pointed beak to grasp insects.

Evidence for Evolution

I. Fossils Found in sedimentary rock, remains or traces of organisms from the past.

These organisms may or may not still exist. Paleontology is the study of fossils.

Dragonfly fossil from

Brazil, more than

100 million years old

Fossils

Dinosaur bones

23,000 year-old mammothtusk in Siberian ice

150 my dinosaur track in Colorado

Ammonites, 375 my Insects

in amber

Petrified tree in Arizona, 190 my

Leaf fossil, 40 my

Darwin’s theory explains the succession of forms in the fossil record.

Transitional fossils have been found that link ancient organisms to modern species

This is an extinct whale with a hind leg limb

Fossils

Remarkable CreaturesBy Tracy Chevalier

Mary Anning 1799-1847

Lyme Regis The south coast of England, on the Dorset-Devon

border. For centuries it was a fishing village and port. The cliffs by Lyme Regis expose a layer of Jurassic

limestone rich with fossils, which has attracted fossil enthusiasts for over 200 years.

Mary Anning In 1812, at age 12, she discovered the first complete

specimen of an ichthyosaur, a marine reptile about 200 million years old (illustration below).

Also discovered first complete plesiosaur and first British pterodactyl

Human Cat Whale Bat

II. Homologous Structures Related species share

characteristics resulting from a common ancestry.

Same structure, different functions are anatomical signs of evolution (forelimbs of bats, humans & whales)

Species

Human

Rhesus monkey

Mouse

Chicken

Frog

Lamprey14%

54%

69%

87%

95%

100%

Percent of Amino Acids That AreIdentical to the Amino Acids in aHuman Hemoglobin Polypeptide

Organisms share the same molecules

The same genetic code written in DNA, RNA and proteins.

Molecular evidence for shared ancestry.

III. Molecular Homologies

IV. Eukaryote StructureAll eukaryotes have similar internal structure & organization

Endosymbioic Theory proposes that eukaryotes originated when largeprokaryotes ingested and assimilated smaller prokaryotes.

Evidence

All eukaryotes have mitochondria for energy transformationThe mitochondrial DNA originates solely from the motherAutotrophs have chloroplasts for photosynthesisBoth mitochondria and chloroplasts grow and divide on their ownBoth resemble modern bacteria.

Porphyridium: DNA in the plastids of this red seaweed is closer in sequence to that of a bacterium than it is to the DNA in the nucleus of that seaweed

Endosymbiotic Theory

Human embryo

V. Similarities Between Embryos

Chick Embryo Human Embryo

Comparing early stages of different animal embryos shows many similarities that are not visible in adult organisms.

“Ontogeny recapitulates phylogeny”

Pharyngealpouches

Post-analtail

VI. Vestigial Structures

Have no apparent function in extant (living) organismThey resemble structures held by their extinct ancestorsDemonstrated in fossil record (pelvis & leg bones of snakes).

The blind mole rat (Spalax typhlus) has tiny eyes completely covered by a layer of skin.

Python with vestigial appendage (hind limb bud).

VII. Biogeography The geographic distribution of a species. Species that live closer to one another tend to be

more closely related than those that do not. Example: Australia has a diverse population of

native marsupial mammals but almost no placental mammals.