Evidence From Fossils Fossils are traces or

remains of dead organisms that have been preserved by natural processes.

Fossils can be formed when organisms are trapped in amber or in ice. Fossils can be formed by the gradual replacement of the organism’s remains by other substances. Fossils can be formed if the plant or animal creates an impression.

The Age of Fossils A fossils relative age can be

determined by observing the layers of sedimentary rock in which the artifact was found.

The age of the fossils found in the layers can be related to the ages of the layers..

This method in which we are able to determine if one fossil is younger or older than another is called relative dating.

The Age of Fossils

Determining when the fossil was actually formed is called absolute dating and depends upon radioactive isotopes.

Over time, radioactive isotopes decay into different elements. By measuring the amount of each element present in the sample, the length of time since the fossil was formed can be calculated.

For example, over time carbon-14 will decay into carbon-12. Carbon dating can be used to date the remains of living organisms that are less than 50,000 years old

Evidence From Comparative Anatomy Organisms may have body

structures which have no function but are similar to more fully developed structures in another organism – these are called vestigial structures.

Humans posses a vestigial structure called the appendix at the base of the small intestine. The appendix is similar to the cecum in rabbits which is used to digest plant materials.

Evidence From Comparative AnatomyThe fact that a similar organ in one species is still

useful is evidence that humans evolved from an ancestor that once had this larger, functional structure.

These vestigial structures support the idea that species have evolved over time as a result of natural selection.

Evidence From Comparative EmbryologyEmbryos of various

organisms are surprisingly similar.

At this first stage of their development, each of these embryos has a tail and slits in its neck.

These similarities indicate that long ago these animals shared a common ancestor.

Evidence From Comparative Biochemistry

Biochemistry is the chemistry of living things.

All organisms store genetic information that is passed on from one generation to the next in DNA molecules in a manner that is almost exactly the same.

Evidence From Comparative BiochemistryProteins are molecules

in living organisms used to build structures, to transport materials, to send signals, to provide defense and to control metabolic activities.

Proteins from different species can be compared. Those species with the fewest differences are more closely related.

Evidence From Comparative Biochemistry

During DNA hybridization, DNA from two different organisms can be compared to see how similar they are.

The more similarities the more closely related the species are.

Patterns of EvolutionMost often as species

evolve from a common ancestor they become increasingly different from each other – this is known as divergent evolution.

Animals that are not closely related but have developed similar adaptations exhibit convergent evolution.

Patterns of EvolutionParallel evolution is

when two distinct species which have evolved from a common ancestor continue to change in similar ways.

Both pterodactyls and birds developed the body structures necessary for flight separately from each other.

Patterns of EvolutionBecause the

environment always includes other living organisms, species frequently change because of, or along with, changes in species around them.

Evolving alongside another species is called coevolution.

Pace of EvolutionResearchers disagree

about the details of the process of evolution.

When evolution occurs through small, steady steps, we call the process gradualism.

When evolution occurs in sudden big jumps with long periods of little or no change, we call the process punctuated equilibrium.

Extinction Extinction is the

disappearance of a species from Earth.

Extinction occurs when a species is no longer able to produce more members of its own type because it can not adapt to the environment.

Human activities have had a significant impact on the rate of extinction.

Before a species becomes extinct they become endangered – examples include the African elephant and giant panda.

Taxonomy Taxonomy is the science

of naming and classifying organisms according to shared characteristics.

Organisms are grouped according to their evolutionary relationships – the smallest group is the species, similar species placed together in a larger group called genus.

Kingdom, Phylum, Class, Order, Family, Genus, Species.

Taxonomy The five main Kingdoms

include: Monera, Protists, Fungi, Plants and Animals.

The scientific name of a species consists of two parts – the first part is the genus, the second part is the species or specific name.

For example a red oak is Quercus rubra, a white oak is Quercus alba. This taxonomic naming system is called binomial nomenclature.

The Search for Human OriginsAbout 130 million

years ago, reptiles such as dinosaurs were the dominant large animals on Earth – in a relatively short period of time, they became extinct.

About 70 million years ago, faced with fewer reptile competitors, an enormous variety of mammals evolved.

The Search for Human OriginsOne groups of mammals

called primates, used opposable thumbs to adapt to life in trees.

The order of primates includes prosimians, monkeys, apes, and humans.

The higher primates including apes and humans are known as hominids.

Hominids: The Earliest Humans Approximately 20 million

years ago, large changes in climate caused forested areas to diminish.

An African Ape evolved and that became the common ancestor of both chimpanzees and humans.

This does not mean that our ancestors were chimpanzees – it does mean that we are closely related.

Why Did Early Hominids Walk on Two Feet.

Our earliest hominid ancestors lived in the trees – due to a changing environment, there was a shift from the forests to the open grasslands.

By being upright in the grasslands, early hominids could see danger approaching.

This could be a tremendous evolutionary advantage and could have easily led to the evolution of life on two feet.

Our own Genus Hominids in the genus

Homo are characterized by having large brains, which sets them apart from all other primates.

Homo erectus is considered to be the first ancestor within our genus.

H. erectus was known to build fires, live in caves, wear clothes and manufacture tools

Our own Genus Homo erectus colonized a

variety of places in Africa, Asia, Europe and Australia.

These early humans included the Neanderthals and the Cro-Magnons, known for there large brains, tools, and clothing.

Our own species, Homo sapiens evolved from H. erectus – exactly where and when is still being debated.