Darwin’s IdeaDescent with modification

Descendants spread into different habitats New habitats necessitated adaptation This accounts for diversity of life

Natural Selection Individuals inherit characteristics well-suited to

their environment Those individuals leave more offspring than others Those offspring are more likely to have well-suited

characteristics Problem: Blending theory of Inheritance

Fossil RecordMost fossils found in sedimentary rock

Due to aquatic preservation, fossils remain largely intact and fossilize in layers

Rock forms in layers, or strata Often sand or silt is deposited on top of existing layer,

compacting it into rock

Fossil Record is formed due to the layering Older rock is “lower” than younger rocks Charles Lyell- UniformitarianismHelps put the puzzle of life together Fossils help show what organisms have as similarities or

dissimilarities due to…..

Geographic Distribution

Another way to understand the similarities Is to see how they are spread out around the globe

Some animals in South American tropics share similarities with African desert animals rather than African tropical animals

Australia is home to more marsupial animals than anywhere else in the world, and had relatively few placental animals.

Echidna

Duckbilled Platypus

Mammals-Marsupials

Structural Similarities

Skeletal structures are very similar in parts of different animals. Human, Feline, Whale, and Bat limbs are similar

Homologous structures structures that indicate common ancestry

Vestigial structures structures that have a major function in one

organism, but less in another

Blind Mole Rat

???Vestigial structure

Developmental Similarities

Developing embryos of different organisms appear similar during maturation.

Organisms start differentiating at different times, with more closely related organisms differentiating later in the process.

Distinctive differences occur later in the process

Molecular Biology In the era of DNA, why don’t we just use the

ultimate similarity of life and compare DNA sequences to see how closely organisms resemble one another? The closer the DNA sequences, the closer

related The less the sequences match, the further

relationship