Transcript What is evolution and what is the evidence

EVOLUTION
What is evolution and what is the evidence for it?
Past and present life forms have evolved from
common ancestors, the lineage of which extends
back in history to simple single celled organisms
Figure 22.7 Descent with modification
The Theory of Evolution explains
1.
2.
3.
The remarkable diversity of life on Earth
The systemic similarities of anatomy, physiology,
and the molecular basis of life and presents a
paradoxical unity of life
The sequence of changes in fossils formed during
geological history
Who evolves?


Individuals do not evolve
Populations do evolve which is seen as change
across generations
Remember that



Individuals do not develop new traits in response to
a changing environment
They do not “try to change for the better”
Individuals use or disuse of organs or behaviors do
not result in changes that will be passed on to the
next generation
So what is evolution?


Evolution = The change in the genetic composition of
a population over time
Changes in gene frequency over time
Theory of Evolution by Natural Selection


Evidence indicates that species evolve by natural selection
over longer time periods
Evolution is validated by evidence from
anatomical homology  similarities between
species due to common ancestry
 Comparative embryological homology  similarities between
species due to common ancestry
 Selective breeding  Breeding organisms for specific traits
 Molecular Biology  Similarities in DNA sequences, protein
structure, etc.
 Biogeography  distribution of living species
 Fossil Record  Form and distribution validate the theory
 Comparative
Study of Homologous Anatomical
Structures






Comparative anatomy of groups of animals or plants show
certain structural features that are basically similar.
Homologous structures are those that are similar in shape in
different types of organisms, but are used in different ways.
Structural similarities imply a common ancestry.
If species actually arose independently (naturally or through a
divine act) each organism should have characteristics uniquely
suited to its nature and environment.
If species evolved, however, then their anatomy is limited by
whatever their ancestors were able to provide.
They will lack some features which would be well-suited to how
they live and they would have other features which aren't so
helpful.
Figure 22.14 Homologous structures: anatomical signs of descent with modification
Pentadactyl (5-digit) Limb




Adapted to different mode of locomotion in
particular environment.
E.g. Bat’s wing and human hand
Illustrates adaptive radiation since basic plan
adapted to different niches.
The more exclusive the shared homologies, the
closer two organisms are related.
Other examples of homologies





Plant: modification of ovary wall or pericarp to aid seed
dispersal.
Vestigial organs: reduced structures that serve no function.
Structures that have lost their function and so are not selected
for and are being lost gradually.
EG of vestigial organs: beginnings of teeth found in embryo
baleen whales, despite adults being toothless.
Small pelvis and thigh bone found in the body wall of whales
and some snakes.
Appendix in humans.
Harmful anatomical homologies



Evolution dictates that these are still present though
inefficient
Laryngeal nerve – from brain to larynx via area
near the heart. Direct path in fish, indirect and
inefficient in giraffes for example
Human knee – rearward articulating knees are
better for walking on the ground, forward
articulating knees are better for arboreal life
Comparative Embryology




Comparative embryology is the branch of
embryology that compares the development of
embryos of two or more species.
The observed similarities and differences may be
used in taxonomic and phylogenic studies
Ernst Haeckel (1866): "Ontogeny recapitulates
phylogeny“ or the development of the individual
repeats the development of the species.
Not literally true but common embryological paths
indicate relatedness
Embryonic Homologies
General Embryonic stages
1.
2.
3.
4.
Fertilization – union of egg and sperm
Cleavage – cell divisions from initial zygote
Blastulation – ball of 100-1000 cells 
vertebrates display differences at this stage
Gastrulation – formation of next stage involving
movements of different tissues
Homologies vs. Analogies





Structural or molecular
The more similar the more closely related
Mammalian limb bone structure, amino acid
sequences for different proteins
Does not include analogous structures – wings of
insects and birds do not indicate common ancestory
only common function.
The human eye and the octupus eye are analogous
because they evolved independently although they
are very similar.
Molecular Biology Evidence





DNA and RNA are universal hereditary molecules.
The genetic code is the same in nearly every organism.
ATP is energy ‘currency’ in all life.
Optical isomers are molecules that are mirror images of one
another. The two forms are D- and L- (we’ll see this in chapter
2 of your textbook). All amino acids in living things are in the
L-form, while all carbohydrates in DNA and RNA are in the Dform.
Physiological processes that are important to living things, such
as cellular respiration, follow very similar metabolic pathways.
Table 22.1 Molecular Data and the Evolutionary Relationships of Vertebrates
Selective breeding




Used by Darwin to introduce and support his theory
of evolution
The ability of a breeder to select desired traits to
pass on to the next generation of a stock
Working with phenotype manipulations
Used to enhance representation of desired
characteristics like high crop yields, resistance to
disease, high growth rate
Domesticated animals and plants


If modern breeds of livestock are compared with
the wild species that they most resemble, the
differences are often huge.
EG Modern egg-laying hens and the jungle fowl of
Southern Asia. Difference between modern maize
(corn) and presumed wild maize (teosinte).
Used historically in agriculture
Artificial Selection vs. Natural Selection



Many different breeds of sheep, cattle and other
domesticated livestock, with much variation between
breeds.
It is clear that domesticated breeds have not always
existed in their current form.
Only credible explanation is that the change has
been achieved simply by repeatedly selecting for
breeding the individuals most suited to human uses.
Artificial Selection for Different Breeds
of Dogs
Effectiveness of artificial selection


Shown by considerable changes that have occurred
in domesticated animals over periods of time that
are very short, in comparison to geological time.
Shows that selection can cause evolution.
Biogeography evidence




Species that are found geographically near each
other should be more closely related
Species that are similar are found on continental
areas that were once connected
Most marsupials in Australia – few others (possums in
south America) explained by continental drift
If life forms arose independently they should be
found in all of the habitats around the world where
they could survive, this isn’t the case
Figure 22.15 Different geographic regions, different mammalian “brands”
New World Vs. Old World Monkeys

Prehensile tails,
arboreal, …

Opposable thumbs,
wider habitat, …
Fossil Record






Fossils found in different strata (layers) of the earth – deeper
generally = older
Different organisms found in different layers / areas
Appearance and disappearance of individual forms does not
detract from overall trends seen in groups
See trends towards increased complexity
Remember that not all materials will fossilize well so there will
be gaps for soft bodied organisms
Results seem to indicate that differentiation initially seemed to
occur more rapidly than subsequent evolution of forms
Figure 22.2 Fossils of trilobites, animals that lived in the seas hundreds of millions of years ago
Summarized evidence from fossil
record



The sequence in which fossils appear matches the sequence in
which they would be expected to evolve, with bacteria and
simple algae appearing first, fungi and worms later and land
vertebrates later still.
Among the vertebrates, bony fish appeared about 420 million
years ago (mya), amphibians 340 mya, reptiles 320 mya,
birds 250 mya and placental mammals 110 mya.
The sequence also fits in with the ecology of the groups, with
plant fossils appearing before animal, plants on land before
animals on land, and plants suitable for insect pollination
before insect pollinators.
Transition to Baleen Whales
Evidence for the sequence



1. Radiometric dating relies on half-life decay of
radioactive elements to allow scientists to date rocks
and materials directly.
2. Stratigraphy provides a sequence of events from
which relative dates can be extrapolated.
3. Molecular clocks allow scientists to use the
amount of genetic divergence between organisms to
extrapolate backwards to estimate dates.
Hominid Evolution Fossils
Many sequences of fossils are known.



These sequences link together existing organisms
with their like ancestors.
EG horses, asses, and zebras, members of the
genus Equus are most closely related to rhinoceroses
and tapirs.
An extensive sequence of fossils, extending back
over 60 million years, links them to Hyracotherium,
an animal very similar to a rhinoceros.
Observed evolutionary change




Microevolution is change in gene frequency
Macroevolution is change in the actual organisms or
species
Observed evolutionary change encompasses
examples where we see that the process is
supported
http://www.phylointelligence.com/observed.html
Theory vs. Law



A hypothesis is an educated guess, based on
observation
A scientific theory summarizes a hypothesis or
group of hypotheses that have been supported with
repeated testing.
A law generalizes a body of observations. At the
time it is made, no exceptions have been found to a
law.
What is theoretical about the Darwinian
View




Darwin’s theory of natural selection took evolution out of
the hands of amateurs and placed it in the realm of
science
In science the word theory means more like a general
hypothesis but more comprehensive
Accounts for many facts and explains a wide variety of
phenomena
As a theory it stands up to thorough and continual testing
by experiments and observations


What is theoretical is not that species have changed
over time, but how the species have done this.
There is a lively debate over the roles of the other
evolutionary forces that can and do change gene
frequencies.