What causes the "struggle for existence"?

Which animal has INCREASED fitness?

Living in a dry, wooded area in the fall season…..

Living in north Canada…in the winter time….

What are these called??

What is it called when humans intervene and create changes in a population?

“descendants” of wild mustard

Evidence of Homology• Homology: the similarity in characteristics that has resulted

from common ancestry• Structures develop from same embryonic tissues

Homologous structures

Homologous structures• Certain structures are similar in different animals – but

used for different functions– This similarity is evidence for a common ancestor

• Forelimbs on different animals have similar bone structures even though they function very differently

Vestigial traitsNot all homologous structures serve important functions.The traits of many animals are so reduced in size that they

are just vestiges, or traces, of homologous traits in other species.

Embryology• There are similarities in development for many organisms

• Early embryos look very similar, even for animals that look vary different as adults

MORE EVIDENCE…..of a common ancestor

Comparative embryology• Development of embryo tells an evolutionary

story – similar structures during development

all vertebrate embryos have a “gill pouch” at one stage of development

EMBROLOGY

Shows evidence of common ancestry.

Different species in the same Class (like

mammals) often have very similar embryos,

even if the adult forms are quite different.

The forelimbs might be legs in an ancestral species, but would be modified as flippers, arms, wings, etc. at a late stage in development; but the pattern in the embryonic

stage would remain similar if not unchanged.

Embryology in plants• Similarities in seedlings of very different kinds of plants suggests a

common ancestry among plants as well

Homology in DNADifferent organisms have similar genes

The more DNA sequences species have in common, the more closely related they are in evolutionary time (the more recently they diverged from a common ancestor).

Homology in DNA

• A comparison of the sequences of dozens of genes that are found in humans and other primates demonstrates the same pattern of relationship

Homology in DNA• DNA sequence comparisons in a wide variety of organisms support

hypotheses of common descent that are implied by physical similarities

Evidence from BiogeographySimilar, but unrelated species evolve in similar

environments.African deserts do contain several species of plants that

resemble cacti, but are from a different family

Fossils tell a story…

the Earth is old

Life is old

Life on Earth has changed

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=H5X0DWnELG-vMM&tbnid=IPc3rRrvhOyIWM:&ved=0CAUQjRw&url=http://en.wikipedia.org/wiki/File:Equine_evolution.jpg&ei=FvoFUaLWJcayqAGFuIH4Dg&bvm=bv.41524429,d.aWM&psig=AFQjCNFUUWJ6XdDLnpdRaEh45NEy8IqeXA&ust=1359432598899164

Name another piece of evidence for common ancestry!

Evidence for common ancestry.

Evidence from theFossil Record

• Over time, the organic material in living things that have been buried degrades and is replaced by minerals, forming fossils– This is a relatively rare since it can happen under only certain

circumstances

Fossil Record Evidence• By the early 1800s fossils remnants of dinosaur were

being studied• Darwin predicted that evidence for evolution between

humans and modern apes would come from the fossils of human ancestors

Fossil Record Evidence Fossils of hominins – humans and human ancestors – provide another

source of evidence on common descent

A key anatomical difference between humans and other primates – bipedal locomotion versus traveling on all fours – is studied by looking at hominin fossils

Fossil Record Evidence

• Homo neanderthalensis – Neanderthal man, the first hominin fossil was found in Germany in 1856

• Homo erectus – standing man – found in Java in 1891• Australopithecus afarensis – first fossil hominin found in Africa

Fossil Record Evidence• “Lucy,” a fossil hominin found in Africa• Australopithecus afarensis type • The fossil skeleton is almost complete• Evidence that this hominin walked upright

When Did Ancient Hominins Live?• Radiometric dating uses the decay of radioactive elements in the fossils to

determine age

• Based on the half-life, scientists can estimate the age of materials like rock

When Did Ancient Hominins Live?• The age of the fossil is calculated based on the age of the rocks

around it• Fossils found in specific age layers of rock are given an age dating that

is consistent with that age layer

• Ardepithecus ramidus - 5.2 to 5.8 million years old

Ardepithecus ramidusJaw of Ardepthecus ramidus

What Is the Missing Link?• The common ancestor of humans and chimpanzees

• The connection between humans and chimps has not been supported by fossil evidence

What Is the Missing Link?• The common ancestor of humans and chimpanzees has not been identified

by fossil evidence– Some critics of evolution cite this in saying that the relationship

between apes and humans remains unproven

What Is the Missing Link?• The theory of common descent stands in spite of the lack of fossil of the

common ancestor– Finding fossilized evidence between any two species extremely

difficult– Strong support of common descent exists in intermediate forms

between modern organisms and ancestors

What Is the Missing Link?• Other fossil records – including that of horses – support common descent

as well

9.4 Are Alternatives to the Theory of Evolution Equally Valid?

• Do the preceding observations enable us to reject any of the three hypotheses that compete with common descent?–Static model–Transformation–Separate types

The Static Model• States that no changes have occurred• Rejected because:–Radiometric data – Earth is older than 10,000 years–Fossil record shows changes

Transformation• States that organisms are separate and change separately• Rejected because:– DNA is similar– Anatomy is similar – Existence of vestigial structures

Separate Types• States that there are separate ancestors for separate species• Rejected because:– DNA similarities– Translation process similarities– Existence of mitochondria for all eukaryotic cells

The Best Scientific Explanation for the Diversity of Life

• Scientists favor the theory of common descent because it is the best explanation for how modern organisms came about

The theory of evolution provides the best explanation for how different types of organisms can look very different, while sharing a genetic code and many cellular aspects