Evidence of Evolution

• Evolution is a process that causes changes in a population's genetic material over time
• Evolution can result in new species, altered genes, and new traits.

Evidence of Evolution

• The Fossil Record
• The Geographic Distribution of Living Things
• Homologous Body Structures
• Similarities in Early Development

The Fossil Record

• Layers show change

Geographic Distribution of Living Things

• Similar environments have similar types of organisms

Homologous Structures

• Have different mature forms or functions in different organisms
• Develop from the same embryonic tissue.

Analogous structure

• Structures have the same function but different origin

Vestigial organs

• Organs serve no useful function in an organism
• Examples include the appendix, miniature legs, or arms.

Early Development

• Development has similarities across comparative embryology, such as in fish, reptiles, birds and humans.

Jean-Baptiste de Lamarck (1744 - 1829)

• French naturalist
• Sought a naturalistic explanation for the diversity of modern organisms
• Proposed the Theory of Inheritance of Acquired Characters in 1809.

Postulates of Lamarckism

• New needs arise from changes in the environment, like light, temperature, etc
• Organisms exert special efforts to fulfill these new needs, like changes in habits or behavior.
• Use and disuse of organs is related to new habits. Greater use of certain organs occurs to meet new needs. Disuse of other organs happens when they are no use in new conditions.
• Lamarck believed favorable acquired characters are inheritable and are transmitted to offspring
• Offspring are born more fit to face new environmental conditions
• Lamarck believed new characters are acquired and transmitted every generation
• New characters accumulate each generation, and result in a new species after many generations

Lamarckism in Giraffes

• A deer-like quadrupedal was the ancestor to the modern giraffe
• Ground vegetation disappeared and trees became the only source of food
• Giraffes developed long necks and long fore-limbs since short-necked giraffes could not reach upper branches and did not survive to pass on their genes.

Lamarckism in Snakes

• Lizard-like reptiles with fully developed pentadactyl limbs were the ancestors of snakes
• Limbs fell into disuse and bodies were stretched to suit their creeping mode of local motion, evolving them into limbless snakes

Lamarckism in Horses

• Ancestors of modern horses (Equus caballus) used to live in areas with soft ground and were short-legged with more functional digits
• Gradually took to living in areas with dry ground
• The change was accompanied by the increase in leg length and decrease in functional digits for fast running over hard ground.

Criticism of Lamarckism

• August Weismann proposed the Theory of Continuity of Germplasm in 1892.
• A multicellular organism is formed of two types of cells: germ cells which have genes for inheritable characters, and somatic cells which have genes for particular organs during one's lifetime only

August Weismann Criticism Details

• Environment affects only somatic cells, and the link between generations is through germ cells
• Somatic cells are not transmitted to the next generation.
• Acquired characters are lost with the death of an organism and have no role in evolution.
• Pavlov trained mice to come for food on hearing a bell, but it was not inherited and replication was necessary each generation
• Kellogg and Bell fed larva of silk moths on reduced quantity of mulberry leaves, and found decreased larva size in next two generations even when these fed normally
• Castle and Philips transplanted the ovary of a black guinea pig into the body of a white guinea pig before sexual maturity and mated the female; observation shows the environment doesn't influence germ plasm.

Significance of Lamarckism

• It was the first comprehensive theory of biological evolution
• It nicely explains the existence of vestigial organs in animals due to their continuous disuse
• It explains the development of strong jaw muscles and claws in carnivores due to their continued extra use
• It stimulated other biologists to look for the mechanism of organic mechanism.

Darwinism (Theory of Natural Selection)

• Proposed by Charles Darwin (1809-1882 A.D.)
• He went on a voyage on H.M.S Beagle and explored S. America, the Galapagos islands and other islands
• Was highly influenced by essays 'On the Tendency of varieties on Depart Indefinitely from the original type" by Alfred Russell Wallace and 'Principle of geology” by Charles Lyell.

Postulates of Darwinism

• Geometric increase
• Limited food and space
• Struggle for existence
• Variations
• Natural selection or survival of the fittest
• Inheritance of useful variations
• Speciation

Darwinism on Giraffes

• Natural selection says the giraffes with short necks had less food to eat because the food resources changed to leaves only on the upper branches
• Short necks could not reach upper branches and did not survive to pass on their genes
• Long neck giraffes survived and reproduced because they were able to reach the food

Dawin's Finches

• Finches are an example of adaptive radiation

Evidence in Favour of Darwinism

• Close parallelism between natural selection and artificial selection
• Cases of resemblance such as mimicry and protective coloration
• Replacement of earlier giant dinosaurs by smaller carnivorous reptiles due to scarcity of food, space and global cooling
• The pedigree of horses and other animals supports Darwinism.
• The correlation between the position of nectaries in flowers and the length of the proboscis of pollinating insects, which can only be developed gradually.

Evidences Against Darwinism

• Inheritance of vestigial organs.
• Inheritance of over-specialized organs.
• He didn't explain the cause of variations and the mode of transmission of variations
• It doesn't include the transitional stages which have no fossil record
• Darwin didn't differentiate between somatic and germinal variations
• It doesn't explain the evolution of terrestrial animals from aquatic animals