Evolution

Biology 20

Six-Kingdom Systems of Classification

Monera

Monera

Phylogeny

Evidence of Evolution

• Evolution: all changes that have occurred in living things since the beginning of life.

Life on Earth Compressed -1 Year January 1st – Solar System and Earth Form March 3rd – First Evolution of Life – Bacteria October 21st – Eukaryotes Appear November 18th – First Complex Multi-cellular

Animals November 28th - Plants and Arthropods Invade the

Land December 2nd - Vertebrates – Early Amphibians

Invade Land December 13th – Mammals and Dinosaurs Appear December 26th – Dinosaurs Go Extinct Dec 31st 4:40pm – First Human Ancestors Appear Dec 31st 11:48pm – First Modern Humans Appear Dec 31st 11:59pm – Start of Recorded History –

Agriculture Dec 31st 11:59:59 – Modern History of the

understanding of the Earth – Geology and Palaeontology Founded

We can divide the history of life on Earth into 4 main stages:

-Precambrian: From the formation of the Earth to 550 million years ago. - - the origin of life, bacteria. - No oxygen in the atmosphere.- Oxygen appears in atmosphere (2 billion yrs ago) to present level 21%. - Eukaryotes appear. No hard parts: bone, teeth, shells, so few fossils.

-Paleozoic Era. 550 to 250 million years ago. Fossils appear, complex multicellular organisms, invasion of the land by plants and animals.

-Mesozoic Era. 250 to 65 million years ago. Appearance of mammals and flowering plants, but the land is dominated by dinosaurs (reptiles).

-Cenozoic Era. 65 million years ago until present. Land dominated by mammals and flowering plants.

Geological Ages

Some Major Mileposts of Life

Fossil Evidence

• Fossils are remains, traces or other direct evidence of past life forms

• Most fossils form from the burial of plants and animals in the sediment

• Most fossils are embedded in sedimentary rock

1. Body Fossils are the actual body or body parts of an organism that has been preserved. These fossils may or may not be altered (fossils that have gone through a chemical change or physical change). The two main types of body fossils are (A) unaltered remains and (B) altered remains…

Body Fossils

A. Unaltered remains of fossils means that the remains have gone through little or no chemical or physical change.

(gastropod)

(saber-toothed cat skull)

(This mammoth died in ice 39,000 years ago)

Body FossilsB. Altered remains- Recrystallization: means that there is a chemical change of the atoms that make up the hard parts of the organism. In this ammonite, the hard parts have been changed to Calcite, a mineral.

Trace Fossils2. Trace Fossils are not the actual body or body parts of life that has been preserved. These fossils show how an organism lived, how it moved, what its feet looked like, how it raised its offspring (its children), what it ate and what its shape was.

(gastropod cast)

This worm tube trace fossil is hollow (the hole goes all the way through it).

(Dinosaur tracks)Do you see the people?

Coprolite:

Fossil Record

• Paleontologists study the fossil record based on the boundaries between the strata, this helps determine the relative age of fossils

• Fossil links combined with modern comparative anatomy allows us to deduce vertebrate descent:– Fish amphibians reptiles

birds and mammals

Evolution of the Modern HorseOne of the few animals for which we have a fairly complete evolutionary record is the horse, as all the main stages of horse evolution have been preserved in fossil form. Over 60 million years the horse evolved from a dog-sized rainforest-dwelling creature, into an animal adapted to plains-dwelling and standing up to 2 metres high.

In the process it traded-in its multi-toed feet, adapted for walking across the forest floor, for single-toed hooves, suited for running over open country.

Geological Time Scale

• Geological history of Earth is divided into eras and periods

• Fossil record provided relative dating of rock layers; top layer of rocks are younger than lower layers of rock

• Absolute dating methods uses radioactive isotopes– Isotopes each have particular

half-life or time it takes for half of the isotopes to decay and become non-radioactive

– Carbon 14 is used to date organic matter; half decays to nitrogen 14 each 5730 year; limited to about last 50,000 years.

Mass Extinctions

• Extinction is death of all members of a species in wild; mass extinctions are extinctions of many species in a short time.

• Five mass extinctions in the fossil record

• Following extinctions, remaining groups expand to fill habitats vacated by extinct species

• Proposed that most mass extinctions are caused by asteroid impact– Impact of the asteroid would create climate

similar to a nuclear winter with worldwide cooling (ice age)

– Cretaceous-Tertiary(64-1.8 million years ago) border has a higher level of iridium, rare in the Earth’s crust but common in meteorites

– Huge meteorite crater of correct age ground in Caribbean Ocean and Yucatan peninsula; suspected sight of impact of meteor that results in dinosaur extinction

• Marine animals fossil record indicates mass extinction occurs every 26 millions year; corresponds to movements of solar system within the Milky Way galaxy.

• Craters

Biogeographical Evidence• Biogeography is the study of

distribution of plants and animals throughout the world

• Current distribution of organisms reflects the evolutionary history, organisms evolve in one location and spread out into other regions; for example, no rabbits are found in South America – they originated elsewhere and did not reach South America

• Physical factors, including locations of continents, limit population ranges

• Continental drift states that continents have slowly moved over time– Explains close puzzle-piece fit of east

coast of South America with west coast of Africa, and other continent edges

– Explains distribution of seed ferns throughout southern continents

– Explains distribution of early reptiles across many continents from time when land was joined

– Explains divided distribution of mammals that evolved after continents parted.

Movement of the Continents

Anatomical Evidence• Many organisms share a unity of plan, for

example, the vertebrate forelimbs contain same sets of bones used for different functions in bat wings, whale fins, etc

• Simplest explanation in having a common ancestor whose basic forelimb plan was modified in succeeding groups as each continued along it own evolutionary pathway.

• Homologous structures are similar in structure derived through descent from a common ancestor

• Analogous structures have similar functions but differ in anatomy and did not derive from the same ancestral structure; for instance, an insect wing and a bird wing

Homologous and Analogous Structures

Embryological Development

• All vertebrates have a tail, notochord and pharyngeal pouches during development

• In humans– The notochord develops into the vertebral

column– The tail becomes the sacral vertebrae

(tailbone)– The pharyngeal pouches become the

Eustachian tubes, middle ear and thyroid gland

• Simplest explanation is that the notochord and pouches are primitive fish features and fish are ancestral to other vertebrates

Comparative Embryology

Biochemical Evidence

• Almost all living organisms use the same basic biochemical: DNA, ATP, many identical enzymes, DNA triplet codes and 20 amino acids

• Similarity of biochemistry is explained by descent from a common ancestor

• DNA base sequences differences is DNA between a number of organisms shows less difference the more closely related they are; for example, 2.5% difference between humans and chimpanzees but 42% difference between humans and lemurs.

Contributors to the Theory of Evolution

• Linneaus– Developed the classification system

(binomial nomenclature)– Linneaus did not believe in

evolution, but his classification system helped to organize many organisms to show similar ancestry

• Buffon– Anticipated many of Darwin’s ideas– Extreme conflict with the church

Other Contributors to the Theory of Evolution

• Cuvier– Founder of paleontology– Also did not believe in

evolution, but did lay the ground work for Darwin’s theory

• Lyell– Geologist– Proposed the Earth is always

changing and is very old

Another contributor

• Larmark– Recorded the first theory of

evolution– Two major disputable points:

•Nature has an innate tendency to evolve in the direction of increasing complexity, determined by the interaction with environment

•Acquired characteristics will be passed onto offspring(not genetically acquired)

Modern Evolutionists

• Charles Darwin– Studied medicine and theology– At 22 became a naturalist on the

HMS Beagle which sailed through the Galapagos Islands

– Proposed the Theory of Natural Selection

• Alfred Wallace– Proposed the same idea as Darwim

Theory of Natural Selection

• Natural selection is a theory that proposes that individuals whose genetic variation best adapt them to their environments will be most likely to survive and pass on those traits.

Darwin’s Discovery of the Theory of Natural Selection

(Fact 1) There is a potentially exponential increases in population Overpopulation

+(Fact 2) Population sizes are relatively

stable (observation)+

(Fact 3) Resources are limited=

(Inference 1) There is a struggle for existence

+

Darwin’s Discovery of the Theory of Natural Selection

(Fact 4) Individuals are unique (observation) Variation

+(Fact 5) Many characteristics are inherited

=(Inference 2) There is a differential

survival, that is natural selection Survival of the Fittest

+(Fact 6) The Earth is very old

=(Inference 3) Through many generations

species evolve Origin of species by inheritance of successful variation

Key Points of Natural Selection• Individual differences are essential for

evolution• The struggle in nature that is of greatest

consequence to evolution is not that between different species; rather, it is the competition within a population of a single species to obtain food, attract a mate, escape predators, etc.

• Only the difference that are inherited are relevant to evolution

• Evolution generally takes a great deal of time and is ongoing.

Sources of Variation

• Mutation create the variation necessary for Natural Selection– Mutations are random changes in the

DNA sequence in a chromosome– Caused by environmental factors

(chemical, radiation or viruses) or in errors when the cell makes copies of the DNA

– Only the mutation to the chromosomes in the sex cells are passed to the next generation.

– Mutations can be harmful, neutral or beneficial. (most are harmful or neutral)

Sexual Reproduction and Variability

• Asexual Reproduction = no variation

• Sexual Reproduction = variation– In sexual reproduction there are two

parents and the offspring inherit a copy of each gene from each parent

– The chromosomes are assorted randomly. So each sex cell has a different combination of chromosomes.

– Sexually reproducing species choose different mates.

Speciation

• Species – a group of organisms that look alike and can interbreed under natural conditions to produce fertile offspring.

• Speciation – the creation of a new species

• Allopatric Speciation – speciation by geographic then reproductive isolation.

Geographical Isolation

– Species become geographically isolated by some physical barrier. A mutation occurs in one group that does not occur in the other.

– Natural selection takes place and the populations evolve independently.

– In time, the changes that occur between the species are so pronounced that if the were reunited they can no longer mate.