Evolution

7.1 What is the Theory of Evolution?

• SCIENTIFIC THEORY: a well-tested scientific explanation that no evidence contradicts

• Theories explain the basic ideas of science. If scientists find new evidence that contradicts the theory, the theory is changed.

• EVOLUTION: a change in populations over time

IDEAS OF DARWIN’S TIME:

•James Hutton– proposes that Earth is shaped by geological forces that took place over extremely long periods of time ---estimates earth to be millions of years old.

•Scientist now believe Earth is 4.6 billion years old!

LAMARCK• JEAN-BAPTISTE LAMARCK – thought that acquiredcharacteristics could be inherited by offspring.

Lamarck thought that you

would gain or lose features if

you used or didn't use them,

and you could pass these new

traits onto your offspring.

PROVEN TO BE WRONG!

Charles Lyell

• processes occurring now have shaped Earth’s geological features over long periods of time.

CHARLES DARWIN: •British scientist whose studies of fossils and different

species established the theory of evolution by natural selection.

•HMS BEAGLE: this ship's voyage allowed Darwin to visit many different places in the world, and study all of those locations' native species.

•DARWIN’S IDEA - “Descent with Modification:”

Present organisms are changed forms of past organisms. Traits are inherited from parents.

7.2 Natural Selection: A mechanism for evolution

•NATURAL SELECTION: organisms with the best traits are selected by nature to survive and reproduce. These genes and traits are then passed on to the next generation.

• EVOLUTION: change in species over time.

• FITNESS: the ability of an organism to survive and reproduce.

•The process of evolution involves changes in populations over extremely long periods of time. Evolution has occurred on Earth over many millions of years.

Four conditions for natural selection to happen1. Overproduction - organisms produce more offspring than can

survive.

2. Genetic Variation - Individual organisms in a population have slight differences.

3. Struggle for Survival - Individuals compete for resources.

4. Differential Fitness - Survivors pass on genes for the best adaptations to their offspring.

ADAPTATIONS:

• Over long periods of time, Natural Selection causes populationsof organisms to be better suited to their environment

• The characteristics of an organism that help it survive and reproduce in its environment are called adaptations.

• Example 1: White fur camoflauges polar bears

• Example 2: Harmless snakes mimic the patterns of venomous snakes

• Example 3: Spots on moth wings resemble eyes of a larger animal

7.3 Types of Natural Selection

• Three Types of Natural Selection:

• Directional Selection – one extreme trait becomes the most selected trait. (e.g. cheetah speed)

• Disruptive Selection – two extreme forms of a trait become the most selected. (e.g. white/black coloration)

• Stabilizing Selection – the average form of a trait becomes the most selected. (e.g. human height)

Example of Natural Selection:• Beetles living on brown tree bark are either brown or green.

• Predator (bird) can more easily see green beetles and will catch them more often than brown.

• Brown beetles live longer and produce more offspring, to whom they pass the gene for brown.

7.4 Evidence of Evolution• Fossils, embryology, comparative anatomy, as well as

biochemical evidence provide evidence for evolution.

• FOSSIL EVIDENCE of EVOLUTION

• FOSSIL : the remains or traces of organisms that lived in the past

• FOSSIL RECORD: the history of life on Earth, based on fossils that have been discovered

Fossil Evidence of Evolution• The fossil record shows how organisms

have changed over time and shows that the Earth is about 4.5 billion years old.

• The fossil record shows that some species have lived then disappeared during the Earth’s history.

• EXTINCT: a species no longer living on Earth

• EX: pelagornithid

• Extinctions occur when there are major changes in the environment and the species is not adapted to survive.

• The fossil record helps scientists to discover relationships between different groups of organisms and determine common ancestors.

Ex: frilled shark (still present – “living fossil”)

Ex: Tiktaalik fossil, 375 million years old, 10 fossils found, a transitional species?

BIOCHEMICAL EVIDENCE•Biochemicals - any chemical made by living organisms.

•e.g. DNA, amino acids, proteins

•All living things use DNA to provide instructions for the building of amino acids into proteins.

•DNA amino acids proteins

•Scientists can analyze proteins in different organisms to determine how similar their DNA is.

•The more similar the amino acid sequence in a protein, the more similar the DNA is between two organisms. •Scientists can determine relationships between organisms by comparing DNA similarity.

•Therefore, DNA is evidence of evolution.

ANATOMICAL EVIDENCE OF EVOLUTION

•COMPARATIVE ANATOMY - a field of biology that involves comparing the body structures of different organisms.

•Homologous Structures - body parts that are similar in structure, but have different functions.

•Analogous Structures - body parts that are different in structure, but have the same function.

•Vestigial Structures - body parts in an organism that have reduced function, or are entirely useless.

•e.g. pelvic leg bones in a whale.

Embryology

• The early stages of vertebrates (animals with backbones) are very similar and give clues to ancestral relationships.

•Gill slits and tails are present in the early stages of human development.

Biochemical Evidence• Closely related organisms have more similar DNA and

amino acids sequences.

7.5 Disproving Spontaneous Generation

• Spontaneous Generation - the idea that living organisms could be produced from nonliving objects.

• Spontaneous Generation was believed to be fact as recently as 200 years ago, but several scientists began to challenge the idea.

• Francesco Redi (1668), John Needham (1745), LazzaroSpallanzani (1745), and Louis Pasteur (1859), all performed famous experiments testing spontaneous generation.

Redi

• Francesco Redi - disproved spontaneous generation with an experiment involving flies, rotting meat, and maggots.

• In the closed jar, flies could not reach meat to lay eggs, so no maggots formed.

•What was Redi's independent variable?

John Needham• John Needham's error - experiment

supported spontaneous generation, but had a major flaw.

• Boiling kills microbes, but he left his jar uncovered. The microorganisms invaded the broth, and turned it cloudy.

Lazzaro Spallanzani• Disagreed with Needham, and corrected Needham's error with his

version of Needham's experiment.

• What did Spallanzani do to correct Needham's flaw?

Louis Pasteur• His famous experiment in 1859 fully disproved

spontaneous generation, by using swan-necked flasks.

• Louis Pasteur ended the debate with his famous swan-neck flask experiment, which allowed air to contact the broth. Microorganisms present in the dust were not able to navigate the bends in the neck of the flask, and the broth remained clear for days.

• With spontaneous generation disproven, a new question was being debated… “So how does life start?”

7.6 How do new species evolve?

•SPECIES: a group of organisms that can successfully produce fertile offspring.

•SPECIATION - the formation of new species

•Speciation begins with isolation.

• GEOGRAPHIC ISOLATION: the separation of a population into two groups, caused by a change in the environment.

EX: A barrier, such as a canyon or river, may

form and divide a population in two.

• Allopatric speciation - when one species evolves into different species because of geographic isolation.

•REPRODUCTIVE ISOLATION - a group of individuals occupy the same area, but are unable to interbreed.

•e.g. different species of frogs occupy the same forest, but each species breeds at different times of the year.

•Sympatric speciation - when two populations of the same species, in the same area, evolve into new species; usually because of reproductive isolation.

7.7 Speciation Occurs at Different Rates• Gradualism - the idea that

speciation occurs at a regular, gradual rate.

• Catastrophism - sudden geological catastrophes cause mass extinctions of species.

• Punctuated Equilibrium - sudden, rapid rates of speciation; followed by long periods of little change.