Modern evolutionary theory, also known as neo-Darwinism, explains how evolution occurs through natural selection acting on genetic variations in populations over multiple generations. Natural selection favors individuals whose genetic variations increase their chance of survival and reproduction, causing gene frequencies in populations to change over time. With enough genetic change over long periods, new species may form. Evidence for evolution comes from fossils that can be carbon dated, showing lineages of organisms changing over time, as well as similarities in cell biology and genetics between related species.
2. MODERN THEORY OF
EVOLUTION (NEO-
DARWINISM)
Includes scientific evidence from genetics
When the allele frequency of a population
changes over successive generations
When the changes are great enough, a new
species may be formed
A species is a group of individuals capable of
interbreeding and producing fertile offspring
3. CHANGES IN EVOLUTION DUE
TO NATURAL SELECTION
A great many offspring are produced but not all of
them survive – population sizes stay fairly constant
‘Survival of the fittest’ – struggle for life for limited
resources e.g. food, avoiding predators and disease,
tolerance to changes in environmental conditions e.g.
temp
Individuals best adapted to their environment have a
selective advantage – they are more likely to survive and
produce offspring
4. EVIDENCE FOR THE THEORY
OF EVOLUTION – DARWIN
SAID……
Each species living today arose from a pre-
existing species
All species have evolved from one ancestral type
Natural selection provides a mechanism for one
species to change into another
5. FOSSILS
K-Ar dating (potassium is found in many rocks and it
decays to argon very slowly)
Can date back 3000 million years
Carbon dating is used on younger fossils (up to 50 000
years old) because it decays faster than potassium
After dating, fossils are put into chronological order
This gives an idea of how one group of organisms
evolved into another
6. PROBLEMS FROM FOSSIL
EVIDENCE
Fossilisation is rare because most organisms
decay
Better evidence comes form cell biology and
biochemistry - by looking at the genetic code
and physiological processes e.g. respiration
These are similar in closely-related organisms
7. NATURAL SELECTION
‘Fitness’ is the ability of an organism to pass on
its alleles to subsequent generations, compared
to other individuals of the same species
The ‘fittest’ individual is one that produces large
numbers of offspring that survive to reproduce
themselves
The genetic characteristics of a population
gradually changes from generation to generation
in response to changes in the environment
8. NATURAL SELECTION
AFFECTS THE GENE POOL
Gene pool is all of the genes and their alleles
present in a species
There is an increase in the frequency of alleles
that give an advantage, and a decrease in the
frequency of alleles that do not give an
advantage
9. GENE MUTATIONS AND
EVOLUTION
Gene mutations are random events that result in a new
allele
Most are harmful
Occasionally, one provides a new phenotype that has a
selective advantage over other individuals in a
population
Over generations, the frequency of mutant alleles may
increase (= micro-evolution) e.g. antibiotic resistance in
bacteria; pesticide intolerance in insects
10. GENE MUTATIONS AND
EVOLUTION continued
Changes at a higher level than species level is
called macro-evolution
This results in the formation of higher
taxonomic groups e.g. new genera or classes.