5- EVOLUTION AND BIODIVERSITY
Evidence for evolu on
● Evolu on → the process of cumula ve change in the heritable characteris cs of a popula on.
● If enough changes occur over me, specia on can occur.
● Specia on → the arising of a new species.
● Charles Darwin was the person who developed the theory of evolu on by natural selec on in
the 1830s.
● There are three ways to prove evolu on: fossil records, animal breeding and homologous
structures.
FOSSIL RECORDS
● Fossils → the petri ed remains or traces of animals and plants.
● Life exis ng 500 millions years ago had a very di erent appearance from today.
● Fish fossils have been found in rocks, 500 million years old or younger.
● Today’s predators are mammals (bears, orcas, wolves, big cats), but these didn’t exist at the me
of dinosaurs.
● The majority of living organisms have no similar form in the fossil record.
● The age of fossils is determined through radioac ve decay of isotopes.
● E.g. C14 is heavier than C12, so a fossil with a higher mass of C14 will be younger. As it gives o
its radioac vity, it slowly decays into a di erent isotope, N14.
● The loss of radioac vity occurs in half-life intervals → half-life is the me it takes for half of the
parent isotope to decay into a daughter isotope.
ANIMAL BREEDING
● By prac cing ar cial selec on, farmers and breeders choose the livestock they believe to have
the best gene c characteris cs.
● A er several genera ons of ar cial selec on, it has been no ced that certain varie es of
animals had unique characteris cs that weren’t present a few genera ons before.
● This provides the evidence that evolu on happens as an accumula on of small changes over
me, however ar cial selec on cannot occur in natural ecosystems.
HOMOLOGOUS STRUCTURES
● → similar anatomical structures found in di erent species.
● E.g. pentadactyl limbs: ve- ngered limbs were found in completely di erent animals like
humans, whales and bats. The shape and number of bones might be di erent, but the structure
is the same.
● This suggests that the animals have a common ancestor.
Species divergence
● Describes specia on.
● When one popula on’s traits change so much that interbreeding with the original popula on
become impossible (incompa bility), so a new species has arised.
tift titititi ti ti tifi
titifi
fitititi ti fi tititifitititifiti titifftiffti ffti ti titi ff ti ff ti ti titi ff
, Adap ve radia on
● → when similar (but dis nct) species evolve quite rapidly from a singular species.
● This happens when varia ons in a popula on lead some members to experience a di erent
niche (role or posi on within an ecosystem) more successfully.
● Due to natural selec on and certain barriers (e.g. a river) , a new species can evolve.
Gradual divergence
● One species can have various splits over
me, crea ng greater diversity between
species.
● This is shown in phylogene c trees.
● In some cases, branches can become so
spaced apart that the species don’t
resemble each other physically anymore →
this happens when species are spread over
a wide geographical area.
● Selec ve pressure → when some versions
of genes (alleles) are favoured over others
for organisms to adapt to the
environmental condi ons.
Transient polymorphism
● Polymorphisms → di erent versions of a
species, resul ng from muta on.
● Selec ve pressure can shi from one allele preference to another.
● E.g. before the industrial revolu on, peppered moths were more likely to survive the because
they could camou age be er than black moths on light surfaces. During the industrial
revolu on, black moths increased in number because the air was lled with black soot, so they
could camou age be er on dark surfaces.
Natural selec on
● → due to the overproduc on of o spring, there is a struggle between compe ng varie es that
leads to survival for some and death for others.
● Bacteria reproduce through binary ssion so iden cal copies are made, this produces li le to no
varia on.
● Species that reproduce sexually instead produce a wide variety of o spring.
● Varia on depends on how successful an individual is and its chance of survival.
● An organism with characteris cs that are well adapted to for its environment is said to be t.
● Natural selec on tends to eliminate individuals with low tness from a popula on.
ti tititi ti fltiti ti ti fltitittff ti fttiti tittti ti fffi ti ti fi fiff titi tttififf
Evidence for evolu on
● Evolu on → the process of cumula ve change in the heritable characteris cs of a popula on.
● If enough changes occur over me, specia on can occur.
● Specia on → the arising of a new species.
● Charles Darwin was the person who developed the theory of evolu on by natural selec on in
the 1830s.
● There are three ways to prove evolu on: fossil records, animal breeding and homologous
structures.
FOSSIL RECORDS
● Fossils → the petri ed remains or traces of animals and plants.
● Life exis ng 500 millions years ago had a very di erent appearance from today.
● Fish fossils have been found in rocks, 500 million years old or younger.
● Today’s predators are mammals (bears, orcas, wolves, big cats), but these didn’t exist at the me
of dinosaurs.
● The majority of living organisms have no similar form in the fossil record.
● The age of fossils is determined through radioac ve decay of isotopes.
● E.g. C14 is heavier than C12, so a fossil with a higher mass of C14 will be younger. As it gives o
its radioac vity, it slowly decays into a di erent isotope, N14.
● The loss of radioac vity occurs in half-life intervals → half-life is the me it takes for half of the
parent isotope to decay into a daughter isotope.
ANIMAL BREEDING
● By prac cing ar cial selec on, farmers and breeders choose the livestock they believe to have
the best gene c characteris cs.
● A er several genera ons of ar cial selec on, it has been no ced that certain varie es of
animals had unique characteris cs that weren’t present a few genera ons before.
● This provides the evidence that evolu on happens as an accumula on of small changes over
me, however ar cial selec on cannot occur in natural ecosystems.
HOMOLOGOUS STRUCTURES
● → similar anatomical structures found in di erent species.
● E.g. pentadactyl limbs: ve- ngered limbs were found in completely di erent animals like
humans, whales and bats. The shape and number of bones might be di erent, but the structure
is the same.
● This suggests that the animals have a common ancestor.
Species divergence
● Describes specia on.
● When one popula on’s traits change so much that interbreeding with the original popula on
become impossible (incompa bility), so a new species has arised.
tift titititi ti ti tifi
titifi
fitititi ti fi tititifitititifiti titifftiffti ffti ti titi ff ti ff ti ti titi ff
, Adap ve radia on
● → when similar (but dis nct) species evolve quite rapidly from a singular species.
● This happens when varia ons in a popula on lead some members to experience a di erent
niche (role or posi on within an ecosystem) more successfully.
● Due to natural selec on and certain barriers (e.g. a river) , a new species can evolve.
Gradual divergence
● One species can have various splits over
me, crea ng greater diversity between
species.
● This is shown in phylogene c trees.
● In some cases, branches can become so
spaced apart that the species don’t
resemble each other physically anymore →
this happens when species are spread over
a wide geographical area.
● Selec ve pressure → when some versions
of genes (alleles) are favoured over others
for organisms to adapt to the
environmental condi ons.
Transient polymorphism
● Polymorphisms → di erent versions of a
species, resul ng from muta on.
● Selec ve pressure can shi from one allele preference to another.
● E.g. before the industrial revolu on, peppered moths were more likely to survive the because
they could camou age be er than black moths on light surfaces. During the industrial
revolu on, black moths increased in number because the air was lled with black soot, so they
could camou age be er on dark surfaces.
Natural selec on
● → due to the overproduc on of o spring, there is a struggle between compe ng varie es that
leads to survival for some and death for others.
● Bacteria reproduce through binary ssion so iden cal copies are made, this produces li le to no
varia on.
● Species that reproduce sexually instead produce a wide variety of o spring.
● Varia on depends on how successful an individual is and its chance of survival.
● An organism with characteris cs that are well adapted to for its environment is said to be t.
● Natural selec on tends to eliminate individuals with low tness from a popula on.
ti tititi ti fltiti ti ti fltitittff ti fttiti tittti ti fffi ti ti fi fiff titi tttififf
