Ch. 14 Principles of Evolution

What is a species?

• There really isn’t a good definition for species, so we need to come up with a working one.

• A species is a group of organisms whose offspring can interbreed.

Evolution of Evolutionary Thought

• Original thought was that all organisms were created simultaneously by God and that they remain fixed and unchanging from the moment of creation.

• This idea was expressed by many ancient Greek philosophers.

Evolution of Evolutionary Thought

• Plato (427-347 B.C.)– Proposed that each object on Earth was

merely a temporary reflection of its divinely inspired “ideal form”

• Aristotle (384-322 BC)– Categorized all organisms into a linear

hierarchy that he called the “ladder of Nature”

Evolution of Evolutionary Thought

• The ideas of Plato and Aristotle provided the basis for unchanging organism.

• This view reigned unchallenged for nearly 2000 years.

Evolution of Evolutionary Thought

• Until the 1700’s, Creationism was the accepted theory.– 1) Each species was created individually by

God.– 2) Earth was the center of the universe.– 3) Man stood as the pinnacle of creation.

Georges Louis LeClerc, “Buffon” (1707 – 1788)

• Suggested that the original Creatoin resulted in a relatively small number of founding species, and that some modern species had evolved through natural processes.

William Smith (1769 – 1839)

• Surveyor, noticed that certain fossils were always found in the same layers of rock.

• He also noticed that fossils and rock layers were in a consistent organization: Younger fossils/rocks near the surface, older fossils/rocks deeper.

Georges Cuvier (1769 – 1832)• Cuvier proposed the theory of

Catastrophism. • Hypothesized that a vast supply of species

was created initially. Successive catastrophes (Ex. Great Flood) produced layers of rock and destroyed many species, fossilizing some of their remains.

• Modern organisms were ones that survived

James Hutton (1726 -1797) & Charles Lyell (1797-1875)

• Developed uniformitarianism• Contemplated the forces of wind, water,

earthquakes, and volcanism.• Said the layers of sediment normally drit to

the bottoms of rivers and lakes• Slow, natural processes alone produced

layers of rock thousands of feet thick.• Therefore, the Earth must be old.

Jean Baptiste Lamarck (1744 – 1829)

• 1st to propose a mechanism for evolution “Inheritance of Acquired Characteristics”– The bodies of living organisms are modified

through the use or disuse of different parts.– Modifications are then inherited by offspring.

• Why modification?– Stated that all organisms have an inherant

drive for perfection.

Lamarck Example

• Ancestral giraffes tried to gain access to additional food by stretching upward to feed on leaves.

• This resulted in their necks becoming slightly longer. Their offspring would inherit these longer necks, then stretch their own necks farther, etc., etc., until we get our modern giraffes.

Lamarck

• Lamarck’s mechanism does not work. • We know that acquired characteristics are

not passed to offspring. (Ex. Scars)• Lifting weights doesn’t make your children

have larger muscles, dying your hair doesn’t give your children the new hair color.

Alfred Wallace (1823-1913)

• Came to the same conclusion as Darwin.• Presented/Described the same

mechanism for evolution in similar papers that were presented to the Linnaean Society in London in 1858.

Charles Darwin (1809-1882)

• Developed the Theory of Evolution and proposed a mechanism for how it worked.

• Darwin published his book On the Origin of Species by Means of Natural Selection in 1859.

• Life’s varitey arose through descent with modification

Natural Selection

• Observation 1: A natural population, has the potential to grow rapidly because organisms produce far more offspring than are required to replace themselves.

• Observation 2: The number of individuals in a population tends to remain relatively constant.

Natural Selection

• Conclusion 1: More organisms must be born than survive. Organisms compete to survive and reproduce.

• Observation 3: Individuals differ from one another in many respects, including ability to obtain resources, withstand environmental extremes, and escape predators.

Natural Selection

• Conclusion 2: These differences help determine which individuals survive and reproduce. This process, by which those individuals whose traits are most advantageous leave a larger number of offspring, is known as natural selection.

Natural Selection• Observation 4: At least some of the

variation in traits that affect survival and reproduction is due to differences that may be passed from parent to offspring.

• Conclusion 3: Individuals that are best suited to their environment leave more offspring, the traits are passed to a larger proportion of the individuals in the next generations.

Evidence For Evolution

• Fossils• Comparative Anatomy• Comparative Embryology• Molecular Biology

Fossils– Transitional forms of animals show forms of

evolutionary change.– We can see changes that have occurred over

time.– Can connect modern species with past

organisms.

Comparative Anatomy

• Comparing similarities between the structures of organisms.

• 3 types of structures– Homologous Structures– Analogous Structures– Vestigial Structures

Homologous Structures

• Structures that are internally similar, but differ in their function.

• Example: Human arm, Dog forarm, Dolphin fin, Bat Wing

• Homologous structures show divergent evolution. Organisms shared a common ancestor, hence the similarities in the structures.

Analagous Structures

• These are structures that perform the same function and look the same, but internally are different.

• Ex. Whale fin, Penguin Wing, Shark Fin• These structures show Convergent

Evolution. Selective pressures from the environment have brought about similarities in the structures.

Vestigial Structures

• These are structures that are present in an organism but no longer have a use. These structures are also normally found in related organisms and are useful.

• Ex. Pelvic bones in whales and certain snakes (have no legs, therefore they do not need pelvic bones). Molar teeth in Vampire Bats.

Comparative Embryology

• The study of looking at how embryos of different species develop and looking at the similarities between them.

• Ex. Gill slits develop in human embryos as well as many other embryos.

• Comparative embryology helps to show that two organisms shared a common ancestor.

Molecular Biology

• Looking at the nucleotide sequence of DNA or the amino acid sequences of protein.

• The more alike the sequences are, the more closely related the two organisms. The less alike they are, the less closely related the two organisms are.

Molecluar BiologyHorse Donkey Chicken Penguin Snake

Horse 0 1 11 13 21

Donkey 0 10 12 20

Chicken 0 3 18

Penguin 0 17

Snake 0