Lecture #33 DARWIN & NATURAL SELECTION Ms. Day Honors Biology

Darwin made two major points in his book called Origins of Species: 1. Many current species are descendants of ancestral species 2. Natural selection is a the way in which EVOLUTION occurs (current “Theory of Evolution”)

Resistance to the Idea of Evolution The Origin of Species = Darwin’s book Shook the deepest roots of Western culture Challenged a worldview that had been prevalent for centuries Earth ONLY ~6000 yrs old It was unchanging!!!!

Lamarck’s Theory of Evolution (1809) Lamarck hypothesized species evolve through use and disuse and inheritance of acquired traits The mechanisms he proposed are unsupported by evidence

Lamarck’s Theory of Evolution Idea called Law of Use and Disuse If a body part were used, it got stronger If body part NOT used, it deteriorated

inheritance of acquired traits Will his kids be born with big muscles because he has them?

WILL THE OFFSPRING BE NICELY PRUNED?

Charles Darwin LOVED nature Sails on HMS Beagle at 22 and voyaged around world Noted flora and fauna on islands off of South America Contributions of Lyell, Hutton and Malthus lead him to his mechanism for evolution species change through natural selection http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

The Voyage of the Beagle Collected specimens of South American plants and animals Observed adaptations of plants and animals that inhabited many diverse environments Main focus of geographic distribution of species = Galápagos Islands near the equator west of South America

The Galapagos Islands Small group of islands 1000 km west of South America Very different climates Animals on islands unique

Darwin returned 5 years later in 1836 NORTH AMERICA SOUTH AFRICA EUROPE AUSTRALIA PACIFIC OCEAN ATLANTIC England Cape of Good Hope Cape Horn Tierra del Fuego Galápagos Islands Darwin in 1840, after his return HMS Beagle in port Equator Tasmania New Zealand Andes Darwin returned 5 years later in 1836

Darwin’s Focus on Adaptation Adaptation= a change in structure or habits, often hereditary, to improve survival and reproduction in environment Adaptation to environment and the origin of new species  are closely related processes EXAMPLE Finches on the islands resembled a mainland finch Finches had different types of beaks adapted to their type of food gathering

LE 22-6 Cactus eater. The long, sharp beak of the cactus ground finch (Geospiza scandens) helps it tear and eat cactus flowers and pulp. Seed eater. The large ground finch (Geospiza magnirostris) has a large beak adapted for cracking seeds that fall from plants to the ground. Insect eater. The green warbler finch (Certhidea olivacea) used its narrow, pointed beak to grasp insects.

Darwin’s Overall Observations Left unchecked, the # of organisms of each species will increase In nature, populations tend to remain stable in size Environmental resources are limited

More of Darwin’s Observations Individuals of a population vary in characteristics with no 2 individuals being exactly alike. Much of this variation between individuals is inheritable.

Darwin’s Overall Conclusions Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals Only a fraction of offspring survive each generation Survival of the Fittest

Darwin’s Conclusion Individuals who inherit characteristics (adaptations) that are most fit (suitable/favorable) for their environment are likely to leave more offspring than less fit individuals Called FITNESS High survival = more offspring = more fit

Darwin’s Conclusion Natural Selection gradual, nonrandom process by which traits become more/less common in a population Acts on PHENOTYPES (adaptations), which influences GENOTYPES only organisms best adapted to environment tend to survive and transmit genetic traits to future generations while those less adapted tend to be eliminated Key mechanism to evolution

http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html Video #4: How Does Evolution Really Work?

Darwin’s Descent with Modification refers to idea that all organisms are related through descent from common ancestor that lived in the remote past the history of life is like a tree

Darwin’s 1st Idea: Evolution What is evolution? All accumulated changes across successive generations in inherited characteristics of populations A change over time in the genetic combination in a population  give rise to diversity Darwins definition = Descent with modification Darwin’s 2nd Idea: Natural Selection If an environment changes over time, natural selection may result in adaptation to these new conditions  new species can also evolve

Evidence for Evolution http://www. sumanasinc Homology a similarities in characteristic traits resulting from common ancestry Anatomical Homologies anatomical resemblances that represent variations on a structural theme present in a common ancestor Called HOMOLOGOUS STRUCTURES Same development, different function

LE 22-14 Human Cat Whale Bat

3. Vestigial organs remains of structures once important in organism’s ancestors Example: tailbones in humans, appendix, wings on ostrich, wisdom teeth in humans

4. Comparative Embryology

Similar genes (DNA), RNA or amino acid sequences 5. Molecular Homologies Similar genes (DNA), RNA or amino acid sequences Example genes shared among organisms inherited from a common ancestor Ex #1: Homeobox is a DNA sequence in genes that regular development in plants, animals and fungi http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.html

Human Rhesus monkey Mouse Chicken Ex #2: Amino Acid/ Frog LE 22-16 % of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide Species Human 100% Rhesus monkey 95% Mouse 87% Chicken 69% Ex #2: Amino Acid/ Protein sequence Frog 54% Lamprey 14%

6. Biogeography the geographic distribution of species Sugar Glider Marsupial Flying Squirrel Eutherian (placental) Some similar mammals that have adapted to similar environments have evolved independently from different ancestors

Paleontologists have discovered fossils of many transitional forms 7. Fossil Records Paleontologists have discovered fossils of many transitional forms Shows variety on organism across time

Key Concepts What is the raw material necessary for the mechanism of Natural Selection? Heritable variations What is the smallest unit of evolution? Populations (NOT individuals) Darwin incorporated Lyell’s gradualism into biological evolution combined with Malthus’ observations regarding populations

What is a “theory” is science? summarizes a hypothesis(es) that have been supported with repeated testing If enough evidence accumulates to support a hypothesis, it moves to the next step—known as a theory—in the scientific method and becomes accepted as a valid explanation of a phenomenon a theory is an explanation or model based on observation theories can be proven or rejected, just like hypotheses.

What is a “theory” is science? Scientific definition of theory is different from everyday meaning non-scientific context of “theory” implies that something is unproven or speculative Scientific definition refers to a comprehensive explanation of some aspect of nature that is supported by a vast (A LOT) body of evidence (data).

Is Evolution JUST a THEORY??? Is it SCIENCE based? http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html Video #1: Isn’t Evolution Just a Theory?

Some Cool Evolution Videos… Poison Newts http://www.pbs.org/wgbh/evolution/library/01/3/l_013_07.html Camouflage “Leaves” http://www.pbs.org/wgbh/evolution/library/01/1/l_011_03.html Evolution of the Eye http://www.pbs.org/wgbh/evolution/library/01/1/l_011_01.html Why Does Evolution Matter Now? (Video #6) http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html