ANTB15 – reading one and lecture 2 notes
Big Picture on Evolution (issue 5 Jan 2007)
“Nothing in biology makes sense except in the light of evolution” – Theodosius
Dobzhansky (1973) when he said this he was referring to the link between genetics
(Mendel 20 century) and evolutionary change (Darwin 19 century). Genetics is
the mechanism, which allows natural selection to occur.
Darwin’s Big Idea
During the 19 century two naturalists, Charles Darwin and Alfred Russel Wallace
independently came up with a theory to explain how evolution occurs. Their shared
insight was that living species were not fixed, but were the product of a gradual
process of change driven by natural selection: the survival and reproduction of
organisms suited to their environment, at the expense of those less successful.
Darwin published his ideas in his book On the Origin of Species by Means of Natural
1. Organisms produce more offspring than survive to reproduce
2. Offspring vary slightly
3. Characteristics can be passed on from generation to generation
4. Those most suited to their environment survive at the expense of those less
Sexual Selection – a variation of natural selection (an animal may have a specific
feature that may make them more vulnerable to predators yet that characteristic is
favoured because it may attract females and in that case they can pass their genes to
their offsprings. An example of this would be the coloured plumage of certain birds.)
Definitions to know
Genotype Genetic characteristic of an individual
Phenotype The physical traits of an individual. Dependent on genotype and
interactions with environment
Allele A version of a gene. Many genes have a number of different
alleles, owing to small variations in gene sequence
Genome The complete set of genetic instructions of an individual or
Sexual Where an offspring’s genes come from two parents
Asexual Where an offspring is genetically identical to its (single) parent
1 Cultures and their explanation for our existence
Inuit – land rose from water and a raven (bird) stabbing its beak into it secured it
Ancient Egypt – Ra arose from a blue lotus flower (interactions with water, air,
darkness and eternity). Ra created a wife and had a son
Caught in a drift
Change is DNA (mutations) can be beneficial, harmful or have no difference (neutral
change). Due to genetic drift the neutral changes in DNA are important. The
frequency of alleles may fluctuate over time and cause evolutionary change.
Due to human’s small founder population the changes in allele frequency probably
had a huge impact on humans.
Biological evolution acts through our genes.
Culture is our systems of beliefs, values and knowledge, it is passed on through
interactions between people. A strong cultural system is language.
Heredity was a mechanism to explain natural selection however Darwin did not
know about genes. Gregor Mendel carried out experiments (peas) that lay the
foundation of genetics. Genes contain the hereditary information.
Tree of life
The idea that all living thing arose from a common ancestor has given rise to the
analogy of the “tree of life”.
There are three main groups: prokaryotes, eukaryotes and archaea (new finding)
Genes are the units of inheritance and can be used to work out evolutionary
Hox genes are found throughout the animal world and can be used to create fruit
flies, cockroch, even human beings. Genes can take on a new function by mutations
(change in DNA sequence). However mutations doesn’t necessarily change the
protein, which the DNA encodes for. Loss of gene funtion may indicate that the gene
is/has become inactive (pseudogenes).
Species- a group of animals or plants that are able to interbreed (and produce fertile
offsprings). New species arise when two populations of the species develop genetic
changes to the point where they are unable to interbreed and produce fertile
offsprings. This could occur when the population become geographically separated.
Inter-species crosses mostly generate no viable offspring (chomosomal or genetic
incompatibilities). Inter-species crosses can result in an offspring but that offspring
will not be fertile (mule).
2 Pathogen evolution
Bacteria’s advantage in the evolutionary sense is that they are able to reproduce
within minutes and therefore they are able to spread rapidly.
Bacteria can form mutations that can tolerate antibiotics (huge advantage)
These drug resistant strains of ba