Homo erectus - AdventuresinScienceEducation

VCE BIOLOGY
UNIT 4

EXAM REVISION

Gary Simpson

Contents


Development of
Evolutionary Theory


Evolutionary
Relationships


Natural Selection


Evidence of
Evolution


Patterns of
Evolution


Change in
Populations


Population
Equilibrium


Hominid Evolution


Biological, Cultural
and Technological
Evolution


Human Intervention


Evolution


Jean
-
Baptiste Lemarck
–

suggested a
theory of acquired characteristics
suggesting that obvious changes could
be made within one generation.


Alfred Wallace
–

proposed a theory of
evolution similar to Darwin’s


Charles Darwin
–

credited with the theory
of evolution based on natural selection to
explain the diversity of species extant and
extinct on planet earth.

Natural Selection

The theory of evolution is based on the
concept of natural selection. This assumes
that in any population:


There is variation with respect to various traits


Some traits are better suited to survival than
others


Not all individuals will survive and reproduce


Those individuals that do survive and reproduce
will have suitable traits


These suitable traits will slowly increase over
time.

Geological Time


Earth believed to
be 4500 million
years old.


Evolution based
upon natural
selection needs a
great deal of time.

Evidence for Evolution


Fossil record


Fossils can take the form of trace,
cast, amber or preserved body
parts.


The process of fossilisation is a
delicate one and is easily
disturbed and the fossils
destroyed.


Fossils can be dated using various
techniques; eg C14 of K/Ar

Evidence for Evolution


Process of Fossilisation


An organism dies and is buried quickly in an
area they can remain undisturbed.


Oxygen is excluded.


Hard parts of the organism leach out which
leaves a cast which is filled by minerals


The mould is buried in sediment which is
covered by repeated layers and left for a
considerable time.


Fossils are remarkably rare!

Evidence for Evolution


Biogeography


Many extant species can
be shown to have arisen
from a common extinct
species.


For example flightless birds
are found on the continents
that once formed the land
mass known as
Gondwana

and offer evidence for the
existence of that land mass.

Evidence for Evolution


Comparative Anatomy


Homologous structures are
structures with the same origin and
similar structure but which may
have different functions.


Analogous structures are structures
which have similar function but lack
a common origin or similar structure.


Evidence for Evolution


Comparative Embryology


The embryo’s of mammals can
be compared to species of
other phyla and to fossil records
to indicate ancestral
connections.

Evidence for Evolution


Comparative Biochemistry
–

DNA


Molecular hybridisation
–

samples of single
stranded DNA from two species are placed
together and encouraged to bond together.
The new strand is then heated. The higher the
temperature reached before the strand breaks,
the greater the number of bonds and therefore
the closer related are the two species.


DNA sequencing
–

when the DNA sequences of
species are compared, the fewer the
differences the closer the species are related.

Evidence for Evolution


Comparative Biochemistry
–

Proteins


Many organisms produce the same proteins
and enzymes. As proteins are the expression
of genes, this suggests that many species
have the same or very similar genetic
information, which in turn suggests a
common ancestral species.

Patterns of Evolution


Divergent Evolution
–

homologous structures are
commonly used as evidence for divergent
evolution where species evolve from a
common ancestor adapting to different
environments.


Convergent Evolution
–

analogous structures
are commonly used for evidence of
convergent evolution where species from
different ancestors respond to similar
environmental pressures in different ways
developing different structures to achieve the
same function.

Changes in Populations


Gene Pools
–

a term used to describe all
the genetic information within a
population.


Individuals within a gene pool inherit
different combinations of alleles due to:


Independent assortment of chromosomes
during metaphase 1


Crossing over of chromatids in prophase 1


Random nature of fertilisation


Random nature of mating

Changes in Populations


Allele Frequency
–

the term used to
describe the abundance of any given
allele in a population, relative to other
alleles at the same locus.


Allele frequencies remain unchanged if:


There is no mutation


The population is infinitely large


The population is isolated


Mating is random


All individuals survive and reproduce
successfully.


Factors affecting population
equilibrium


Founder Effect
–

describes when a few individuals
leave an existing population and establish a new
population somewhere else. The new population
may have a gene pool with limited diversity and
different allele frequencies to the original
population.

Factors affecting population
equilibrium


Genetic Drift
–

chance events increase or
decrease variations in alleles over time.
These chance events may cause an allele
to disappear from the gene pool or to
become the only allele present for a
particular trait. This is more likely in small
populations than large populations.

Factors affecting population
equilibrium


Bottle Neck
–

this is an extreme example
of genetic drift. A very small group of
individuals of a species may survive some
catastrophic event and are then the basis
of future generations, but with very limited
genetic diversity and a reduced ability to
adapt to future environmental change.


Factors affecting population
equilibrium


Variation


Within species


Environmental effects


Genetic Effects


Sexual Reproduction


Adaptations


Speciation
–

when a
new species arises
from existing species.


Extinction
–

when a
species disappears
from the planet.

Allopatric Speciation


Individuals within a population are
separated by a barrier that prevents
migration.


Difference selection pressures are applied
to the two populations.


The allele frequencies of the two
populations diverge.


Over time two species arise that can no
longer successfully interbreed.

Isolating Mechanisms


Pre
-
reproductive


Things that stop populations physically
mating; eg. Geographic features, timing of
breeding, behavioural mechanisms,
morphological mechanisms.


Post
-
reproductive


Phenomenon that stop offspring
developing into adults; eg. High gamete
mortality, high zygote mortality, hybrid
sterility.

Evolutionary Relationships


Phylogenetic trees
–

start with a common
ancestral species and
then show the points at
which new species have
branched off.



Cladograms
–

a
diagram showing the
relationship between
organisms based on
their evolutionary history.

Determining Species
Relatedness


DNA sequencing
–

the more similar the
sequence of bases of two species the more
likely they are to share a common ancestor.


DNA
-
DNA hybridisation
–

DNA is extracted
from 2 species and caused to combine.


Mitochondrial DNA
–

mtDNA mutates at a
steady state and can be used as a molecular
clock.


Chloroplast DNA
–

has changed very little
over time.


Proteins
–

comparing the amino acid
sequences of proteins.

Hominid Evolution


Primates
–

a group of
mammals that have binocular
vision, flat nails, exposed,
sensitive finger pads, and
large brain relative to body
size.


Hominins

–

a sub
-
group of
primates that walk upright and
have relatively large brains.


Hominids
–

a sub
-
group of
hominins

containing all the
human and human like
species.


Genus Homo
–

our genus of
which we are the only extant
species.

Common Features of Hominids


Relatively large brain for body size


5 digits on hand and feet


Opposable thumbs


Large forward facing faces


4 upper and 4 lower incisors


Flexible skeletons


Generally small
litters with extended
periods of intensive parenting.

Human Evolution


Out of Africa Theory


Homo erectus

arose in Africa and migrated
throughout the world. At a later point in
time
Homo sapiens

arose in Africa and then
migrated throughout the world replacing
H.
erectus
.


Regional Continuity Theory


Homo erectus

arose in Africa and migrated
throughout the world. At a later point in
time
Homo sapiens

independently arose
throughout the world replacing
H. erectus
.


Biological, Cultural and
Technological Evolution


Cultural


Technological


Biological


Human Intervention


Selective Breeding


Domestication


Artificial Cloning


Genetic Engineering