Evidence of Evolution

• Fossils• Vestigial Structures• Embryonic Development• DNA sequences

Fossils • Preserved remains or imprint of ancient organisms

• Form mostly when sand/silt settle from water over dead organism sedimentary rock

• Fossil record is incomplete:– Most living things leave no trace;– Fossils vulnerable to weather &

erosion;– Soft parts do not fossilize well.

• Provide much of what we know about life’s history.

• Fossils are dated by a chemical method called radioisotope dating.

Fossil Formation

We can only date igneous rock using radioactive isotopes;Sedimentary rock is dated using layers of igneous rock above and

below it.

Radioactive Isotopes Are Used to Date Fossils / Geological Layers of the Earth

Geology - Law of Superposition(add to notes)

Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top (provided that there is no overturning).

Newest layer

Oldest layer

Plate Tectonics

affects biogeography (how species

are distributed in geographical

areas)

What drives plate tectonics?

Analogy: hard-boiled egg

Fossil Record & Human Evolution

“Lucy” (Australopithecus afarensis ) -- discovered 1974, Ethiopia; ~3.4 m.y.a.; 40% complete

Hip structure shows bipedal upright walk, brain capacity comparable to that of ape

Lucy replica Reconstruction

Some fossils are famous!

An artist’s interpretation shows how a 4.4-million-year-old female Ardipithecus

may have looked

“Ardi” (Ardipithecus ramidus ) ~4.4 m.y.a. – Eastern Africa – fossils found 1990’s - 2004

Evolved a few million years after humanity’s evolutionary family diverged from a lineage that led to chimpanzees, but it is not clear exactly how this species is related to other early hominids.

Fossils of this ancient hominid display a mixture of traits suitable for two-legged walking and tree climbing

Some fossils are famous!

“Living Fossils”

Species that are relatively unchanged from their distant ancestors:

Coelacantha living fossil fish

Horseshoe craba living fossil

arthropod

Embryonic Development

Ex:

Vertebrate embryos share a tail and gill slits at early stages of development, revealing the presence of genes that are no longer expressed in the adult.

Human Embryonic Development

Vestigial StructuresInherited, No Longer Functional

Atavistic Traits are thought to be caused by the expression of genes that had been silenced during evolution.

(Atavus = grandfather/ancestor expression of an ancestral trait)

X-ray image of an atavistic tail found in a

six-year old girl(from Palomar.edu)

Homologous StructuresSimilar Structure from Common Ancestry

Lizard Human Cow Bird Bat Whale

Analogous StructuresSimilar Function, NOT Common Ancestry