Evolution Notes

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The History of Life on Earth Earth has been home to living things for about 3.8 billion

years Fossils provide evidence of earlier life

Fossils – the remains of organisms preserved in the Earth Types of Fossils:

Hard body parts, such as bone Minerals replace parts of organism Prints made by organisms Original remains of entire organism Fossilized Bone

Imprint Fossil Insect in Amber Woolly Mammoth

History of Life Continued…

The age of fossils can be used to determine the history of life on Earth Relative Dating – by

comparing one fossil with another fossil, it can be determined if one fossil was formed before or after another

Absolute Dating – by measuring radioactivity, the exact age of a fossil can be determined

Relative Dating

Absolute Dating

History of Life Continued…

Once the age of fossils is determined, the fossil record can be established Fossil Record –

the information about the fossils found in a particular location

The fossil record can be used to determine when a species lived or died

The History of Life Continued… The fossil record indicates that more complex organisms

developed on Earth over time At first, all living things lived in the oceans

First came unicellular organisms (3.8 billion years ago) These are organisms made of a single cell. Over time, different types of unicellular organisms

developed – bacteria, archaea, protists, etc. Then came multicellular organisms (1.2 billion years ago)

These are organisms made of many cells Then came life on land (500 million years ago)

500 million years ago the first multicellular organisms moved from water to land

First came plants, fungi, and insects, then came amphibians and reptiles, finally came birds and mammals

The History of Life Continued… Although organisms were constantly developing, Earth’s

history also includes mass extinctions Mass Extinction – when huge numbers of species have

died or become extinct in a very short time Permian Extinction (250 million years ago)

In this extinction, 90% of the species living in the oceans became extinct

Occurred when Earth’s land masses joined together Cretaceous Extinction (65 million years ago)

In this extinction, more than half of the species on Earth (including dinosaurs) became extinct

This was caused by a meteorite collision – the evidence of this is the Chicxulub Crater

The History of Life Continued…

Life Changes Over Time Because of the fossil record, in the

past 200 years scientists have explored the idea of evolution Evolution – the process through

which species change over time Evolution results from a change

in DNA (a mutation) Jean Baptiste de Lamarck (early

1800s) – he was the first scientist to propose an idea of how life evolved He proposed that an organism can

acquire a trait during its lifetime and pass that trait on to its offspring

This idea could not be supported by evidence so it was not accepted as scientific fact Lamarck’s Giraffes

Jean Baptiste de Lamarck

Life Changes Over Time Continued… Charles Darwin – A British Naturalist who spent 5 years

on the H.M.S. Beagle He observed animals, especially on the Galapagos Islands For example, when observing finches, he saw a variety of beak

shapes that were adapted to what they ate and where they lived

Charles Darwin

Life Changes Over Time Continued… Darwin proposed the idea of evolution through the

process of natural selection Natural Selection – members of a species that are best

suited to their environment survive and reproduce at a higher rate than other members of the species

Natural selection occurs through the continuous cycle of genetic mutation and reproduction

Key Principles of Natural Selection:1. Overproduction

2. Variation

3. Adaptation

4. Selection

Natural Selection Overproduction:

When a plant or animal reproduces, it usually makes more organisms than can survive

Variation: Within a species there are natural differences in traits caused

by differences in DNA These natural differences are passed from one generation to the

next Sometimes there is a change in DNA, a mutation, that is also

passed on

OverproductionVariation

Natural Selection Continued… Adaptation:

Sometimes a mutation occurs that makes an organism better able to survive than others

Adaptation – any inherited trait that gives an organism an advantage in its particular environment

Selection: Species with an adaptation are more likely to survive and

reproduce This adaptation becomes more common with each generation The environment is selecting for this trait

Adaptation Selection

Evolution Through the process of natural selection, new species

develop from earlier species In 1859, Darwin’s observations resulted in the publication of On the

Origin of the Species, a book about evolution through natural selection

Speciation: evolution of new species from an existing species May occur when the environment changes Isolation is essential to speciation

Isolation: For a species to develop into two new

species, two populations must be prevented from reproducing with each other

When separate, they each develop different mutations, which, over time, result in different species

Speciation of Salamanders

Evidence for Evolution Observations provide evidence for theories

In order to understand the importance of Darwin’s work, it is important to understand the term scientific theory

Scientific Theory: A statement based on fact and observation A theory that has been widely accepted is used to explain and

predict natural phenomena Examples of Scientific Theories:

Theory of Gravity The Big Bang Theory Evolution through Natural Selection

A scientific theory is NOT a guess or an opinion!!!

Evidence for Evolution

Fossil evidence supports evolution Geographic evidence

about fossils shows that two species with a common ancestor can develop differently in different locations

Ancestor – an early form of an organism from which later forms descend Scientists can

determine modern plants and algae have a common ancestor in fossil algae Fossil evidence for the evolution of

the horse

Evidence for Evolution Continued Biological evidence supports evolution

The structure of living things: Vestigial organs – physical structures that were fully

developed and functional in an earlier group of organisms but are reduced and unused in later species

Example – hip and femur bones in whales Homologous Structures – similar structures with different

functions: Many different species share similar structures, but they

are used differently by each species This indicates a common ancestor Example – arms and wings

Vestigial Organ

Homologous Structures

Evidence for Evolution Continued… Biological Evidence Continued…

Development of living things: Similarities in development – scientists have seen that

many organisms are very similar during early stages of development, when an embryo

Genetic evidence supports evolution Scientists can tell how closely related organisms are by comparing

their DNA Example – clock gene

genetic

Similarities in Development

Cladograms Cladogram – a visual representation of the evolutionary

relationship among species based on the evidence collected Show how closely (or distantly) related two species are Show which species evolved before or after other species Show the similarities between more closely related species

Evolution of Humans

Early humanlike species: Ardipithecus – one of the oldest hominid fossils found Australopithecus afarensis – Lucy – 3.5 million years old, 1

meter tall Fossils are 500,000 to 6 million years old Each species is more humanlike than the one before Over time, some hominids went extinct and others evolved.

Eventually, the only one left was us, Homo sapiens.

Evolution of Humans Continued… Neanderthals and Cro Magnons lived at the same time as

modern humans, but went extinct Neanderthals – Homo neanderthalensis

Lived 130,000 to 35,000 years ago Larger skulls with sloping foreheads, but shorter than

modern humans Cro Magnons - Homo sapiens sapiens

Lived 35,000 to 10,000 years ago Tall with large and round skulls Skilled hunters and toolmakers

Modern humans: Modern humans are Homo sapiens (“wise human”) First fossil evidence of modern humans is about 100,000 years

old

Cro Magnon Skull