Natural Selection, Speciation & Evolution Flashcards
evolution
Evolution is the change is species over time. It is usually very gradual, but in the correct circumstances, can be reasonably rapid.
what does evolution lead to:
one species forming 2 (or more) new species
OR
a change in a species without the formation of a new species
how does evolution occur
Evolution occurs in a species NOT in an individual
it what two ways does evolution occur
convergent evolution
divergent evolution
convergent evolution
(unrelated species become more similar)
occurs when different species
change in a very similar way
due to the species experiencing
the same selection pressures.
divergent evolution
(one species changes into two species)
occurs when different adaptations occur (and are selected for) in separate populations of the same species. This normally occurs when the populations live in areas with different environments
How do we know that evolution occurred?
a) we can see progressive change through fossils
b) many species have vestigial structures.
what does Charles Darwin say about evolution
- proposed that evolution
occurs through the process of
Natural Selection. - this theory relies on naturally
occurring variation within
populations that provides
some of the organisms with a
survival advantage.
why is charles darwin important in this topic
his theory of evolution is most accepted
what did his theory rely on and how was it veiwed?
- relied on favourable traits being inherited (his theory was
formed long before knowledge of DNA/inheritence) - was viewed as radically “anti-church”
do adaptations occur because a species needs them, why?
It is important to realise that adaptations don’t occur because a species needs them. They arise through chance mutations and they help the individuals of that species survive.
what is a reason that some species go extinct
Plenty of species have gone extinct though - largely due to the fact that the DNA didn’t mutate in a way that provided a benefit (or because the environment changed too quickly for the allele frequency for the beneficial adaptation to increase).
Natural Selection
Natural Selection is a theory used to explain how the frequency of alleles changes within a popuation.
what is needed for natural selection to occur
For natural selection to occur, there must be variation within the population. This variation occurs by chance through mutation which creates new alleles.
what happens when an mutation gives an advantage in its habitat
If the mutation gives an organism an advantage in its habitat, it is more likely to survive, reproduce and pass the beneficial gene on to its offspring
what happens when a trait continues to be beneficial
If the trait continues to be beneficial, its presence in the population will increase over generations
what does the process of natural selection result in
The process of natural selection results in some individuals having more offspring than others.
what is a selection agent + egs
The factor that acts on the population and favours some individuals more than others is known as the selection agent. It can include climate, predators, food availability or disease.
how is Charles Darwins’ theory described
Although he did not come up with the phrase, the term “survival of the fittest” is often used to describe Charles’ Darwin’s theory of natural selection.
what does the survival of the fittest phrase mean
The “fittest” organisms in this sense are the ones that are best adapted to their environment and are most likely to survive and reproduce
why did Alfred Wallace receive no credit for the same theory?
Darwin was actually lucky to be credited
with this theory because Alfred Wallace
came up with the same theory at the
same time but Darwin’s book was
published first so he got all of the glory.
what leads to the formation of a new species
an important process in evolution is speciation which can lead to the formation of a new species
Whether two individuals are from the same species used to be determined by the following rule:
if they could breed together under natural conditions as produce a fertile offspring, then they are of the same species.
how does DNA tell us if two individuals are the same species
Now they also use DNA to test whether two individuals are the same species. >1% difference is usually regarded as different species.
speciation
Speciation is the process in which one species splits/diverges into 2 or more new species. It’s how new species appear in the fossil record.
what are the three stages of speciation
It consists of 3 stages:
- variation - isolation - natural selection
variation
must be present in the initial population or the subdivided populations as the process of speciation involves natural selection.
isolation
the population must become geographically isolated so that gene flow can’t occur. The populations can become separated by the formation of rivers, dams, mountain ranges, deserts, clearings under power lines, car parks, salinity, soil pH etc.
natural selection
Natural selection occurs independently in each population (with each having a different selection pressure).
sub species
If the individuals in the 2 sub-populations look have evolved to look different but can still produce fertile offspring, they are called sub-species.
new species
If they have evolved to look different and can no longer breed to produce fertile offspring, they are new species and reproductive isolation has occurred.
can sub populations meet up again?
The 2 sub-populations may meet up again some time in the future
Our species is called?
Our species is called Homo sapiens.
did we evolve from monkeys or cavemen
we did NOT evolve from monkeys (although we do have a common ancestor)
- we did NOT evolve from cavemen
phylogenetic trees
they are used to show which groups are most closely related
who are the two closest living relatives of humans
two closest living
relatives are chimps and gorillas.
primate
The order “primate” can be divided into several groups (each classified at the level of family)
Hominoids:
Hominoids:
the most recently evolved group of primates (no tail)
Hominins
The family Hominoid can be further divided and humans
belong to a group called Hominins.
what is the main feature of Hominins and what structural changes occured for this?
The main feature of Hominins is that they are fully bipedal (walk on two legs). This involved structural changes to the pelvis and skull (where the spinal cord comes out changed position which allowed greater balance on two legs)
Homo habilis
- handy man (evidence of tool use)
- larger brain (more protein in diet?)Homo
Homo erectus
- used fire
- even larger brain (more protein in diet)
- evidence of care giving
Homo sapien
- cultural evolution
- self-aware
As species become more modern:
(slide 42)
- flatter face
- lower jaw shortens
- forehead less slanted/more vertical
- cranium capacity increases (which can hold a
larger brain but that isn’t part of the skull)
Homo neanderthalensis - How did that connection happen?
They lived at the same time as our species but are not our ancestors. Possiby through divergent evolution from Homo erectus.
what does DNA say about neanderthals and our species
DNA evidence suggests that
breeding occurred between
neanderthals and our species but not
all offspring were fertile (so different species)
