C&C Ch. 5 Flashcards
give examples of how eyes are adapted to different functions in organisms?
- eyes of predators have special adaptations to break the camouflage of prey
- many underwater predators that eat transparent marine animals have eyes with special contrast-increasing systems, including UV vision and polarised light vision
how are bird wings adapted for flying?
the bones in the wings are hollow, with internal struts
how are butterflies adapted for feeding?
have long tongues to reach deep down into flowers and suck up nectar
how are flowers adapted for seed dispersal?
they have high visibility to insects and advertise themselves by scents, as well as rewarding visitors by nectar
how are frogs and chameleons adapted for feeding?
they have long tongues that can shoot out and capture insect prey on their sticky tips
give 2 examples of how animals are adapted to escape predators
- silvery colour of many fish species makes them difficult to see in the water
- some animals have cryptic coloration, with extraordinarily close mimicry of leaves or twigs, or of other poisonous/stinging species
give examples of adaptations in cells
- cell divisions and cell movements are powered by tiny motors made of protein molecules
- Proof-reading of newly produced DNA occurs to prevent harmful mutations
- protein complexes in cell surfaces selectively allow entry of some chemicals, but prevent others from getting in
give examples of how the behaviour patterns of birds are clearly adapted to their ways of life?
- nest parasites like cuckoos remove the host species’ eggs or young from the nest, leaving the hosts to raise their young; host species adapt by becoming more vigilant
ants that grow fungus gardens have evolved behaviours including
weeding out spores of fungi contaminating their decaying leaves
why did people before Darwin and Wallace believe in the existence of a creator?
there seemed no other way to account for the astonishing detail and apparent perfection of many aspects of living organisms
what does the argument from design overlook?
the possibility that there could be natural processes which can account for living creatures as complex natural productions, without the need for a designer.
define artificial selection
the modification of organisms by humans; selective breeding from animals and plants with desirable characters
what did Darwin argue about artificial selection?
- very striking changes can be produced over a time-frame that is short on the scale of the fossil record of evolution
give an example of artificial selection in plants
- we have developed many different strains of cabbages, including cauliflower and broccoli
how have domesticated dog species been produced over the past few 1000 years?
dog breeds have been produced by artificial selection from a single common ancestral species, the grey wolf.
why is the success of artificial selection possible?
because heritable variation exists within populations and species (slight differences between normal individuals)
what does artificial selection show?
- individuals within domesticated species must have been different from one another
- many differences are heritable
if differences were merely due to the way the animals or plants were treated,
selective breeding and artificial selection would have no effect on the next generation
how may different breeds of dogs differ in ways other than appearance and size?
- mental traits such as character, disposition, intelligence
- interest in scents
- inclination to fetch/carry/swim
aside from heredity, what may influence the traits of domesticated animals?
environmental circumstances such as good care and treatment
give an example of artificial selection for plants
- qualities of different apple varieties are heritable differences
- include adaptations to different human needs (eg early/late harvesting, suitability for cooking and eating)
is perfection ever attained for all desirable traits?
no
describe discrete character differences as a form of variation
- eg eye and hair colour
- variants controlled by differences in single genes, and unaffected by environmental circumstances
describe continuous variation as a form of variation
- eg height and weight
- often significantly affected by environmental conditions
why was there an increasing height of successive generations during the 20th century?
not due to genetic changes but to changes conditions of life, including better nutrition and fewer serious illnesses during childhood
how can the amount of continuous genetic variability be measured? how is this useful?
from resemblances between relatives of different degrees
- allows breeders to predict the characteristics (such as yield of milk of cows) that offspring of different parents will have
what it is called when some individuals in the population have a variant sequence of a gene?
molecular polymorphism
what percentage of the DNA letters differ when we compare the same gene’s sequence between different people?
fewer than 0.1%
where is variation generally higher?
in the presumably less important regions of the genome that do not code for proteins than in the coding parts of genes
describe the diversity in natural species that live in geographically separated populations
the amount of diversity in such species as a whole is greater than within a single population, because there are differences between populations
why are the differences between populations for humans very slight in comparison to other species? what is the implication of this?
- because humans can move freely between populations.
- human populations are thus distinguished with respect to only a small fraction of our genomes
give an example of how the same character may give high fitness in one species, but not in another
speed is not important for fitness in a lizard that evades predators by cryptic coloration
give an example of how some animals may avoid predators by frightening them away
some butterflies have eye spots in their wing patterns that can be suddenly displayed in order to alarm birds
example of severe selection
when diseases wipe out most of a herd or a plant crop
how are humans still evolving?
our diet differs from that of our ancestors, and our teeth can function well on modern soft foods even if they are not very strong
why is there no longer very pronounced natural selection for strong teeth
- high sugar content in modern teeth -> tooth decay, abscesses that can be fatal
- dental care can solve these problems
why is there a new selection pressure to change our metabolism so as to tolerate our changed diet?
due to the increased frequency of late onset diabetes in human populations, with high mortality for sufferers
illustrate selection of an advantageous mutation by considering the arms race between humans and rats
- rat poison warfarin kills rats
- binds to an enzyme needed in the metabolism of vitamin K, important for blood clotting (-> prevents it)
- resistant rats were once rare because their vitamin K metabolism is changed, reducing growth and survival
warfarin-resistant rats are an example of
the cost of resistance
where do warfarin-resistant rats exist despite the cost of resistance?
in farms and towns where warfarin is used - only resistant animals can survive so there is strong natural selection despite the cost
why are certain components of genetic material always maintained despite not increasing fitness?
because they can multiply within the genetic material itself, like parasites in the body of their host
describe cancer as an example of natural selection driving evolutionary change
- disease is often caused by a mutation that increases the mutation rates of other genes
- if mutations occur at a high frequency, some may affect cell multiplication rates, and a fast-multiplying lineage may appear
- as time goes on, more and more of the cells will descend from cells carrying mutations in other genes which confer faster and faster growth so the cancer becomes more aggressive
distinguish between selection at the level of species and the level of individuals
- species with large body sizes, which tend to have low population sizes and low rates of reproduction, are more vulnerable to extinction than species with small bodies
- selection between individuals of the same species often favours larger body size, probably because larger individuals have greater success in competition for food or mates
why is selection on individuals within species likely to be the most important factor?
since it produces the different range of body sizes in the first place, and usually operates much faster than selection at the species level
why do we expect that evolution will usually proceed by fairly small adjustments to what has gone before, rather than by sudden jumps to radically new states?
- if one component is changed drastically, it may not function well in combination with other parts that remain unchanged.
- when new adaptations evolve, they will usually be modified versions of pre-existing structures, and will at first often not be the optimum functional engineering design solutions
why can distantly related organisms living in similar circumstances sometime look more similar than closer ones?
- sometimes, similar solutions to a functional problem have been evolved independently in different groups
- resulting in very similar adaptations that differ considerably in detail because of their different histories
- eg wings of birds and ants
how can true evolutionary relationships be discovered when morphological similarities and differences are misleading?
using evidence from DNA sequence similarities and differences
why can the fact that evolution have no foresight be problematic?
this may result in features which lead to their extinction when conditions change radically
give an example of how adaptation can lead to extinction
- sexual competition among males can lead to structures that severely reduce their survival ability
long-lived organisms often evolve ———
very low fertility
when can long-lived organisms with a very low fertility do well?
if the environment is favourable, and there is low annual mortality of breeding adults.
when can long-lived organisms with a very low fertility do bad?
if the environment deteriorates and mortality increases, for example because of human disturbances, this may cause a rapid decline in population number
when would species which evolved to occupy an extremely specialised type of habitat be vulnerable to extinction?
if the habitat disappears to environmental change
give an example of imperfect selection
the nerves that carry information from the light-sensitive cells of the vertebrate eye are in front of, rather than behind, the light sensitive retinal cells
give 3 reasons why natural selection does not necessarily produce perfect adaptation
- there may not be time to adjust every aspect of a piece of biological machinery to its best-functioning state
- the tinkering aspect of selection, modifying what has gone before, constrains what selection can achieve
- an improvement in one aspect of the functioning of a system may have a cost with respect to some other function
why is the speedy evolution of antibiotic resistance not surprising?
- bacteria multiply fast and are present in enormous numbers
- any mutation that can make a cell resistant is sure to occur in a few bacteria in a population
- if the bacteria are able to survive the change to their cel functions caused by the mutation and multiply, a resistant population can build up
antibiotic resistance can spread between
bacteria, even ones of different species
what happens if one stops treatment while some bacteria remain present?
their population will inevitably include some resistant bacteria, which can then spread to other people
why is HIV so difficult to treat?
the HIV virus mutates within infected patients treated with a single drug, and evolves resistance so that the treatment eventually fails
2 examples of how human activities are causing evolutionary changes in organisms
- killing elephants for their ivory had lead to increased frequencies of tuskless elephants
- swallowtail butterflies with small wings, which are poor flyers, are being selected in fragmented natural habitats, as individuals that do not fly far are more likely to remain within suitable habitat patches
describe how the 40 year study by Peter and Rosemary grant of two species of Darwin’s finch, the ground finch and the cactus finch on the island of Daphne in the Galapagos island was carried out
- team systematically ringed and measured every bird hatched on the island, and the offspring of every female were identified
- survival through life was followed and related to measurements of size and shape of body parts
what did pedigree studies in the 40 year study show?
variation in beak characters has a strong genetic component, so that offspring resemble their parents
fact of beak size and shape on efficiency of feeding
- large, deep beaks allow birds to handle large seeds better than small, shallow beaks
- reverse is true for small seeds
describe how episodes of severe drought in the Galapagos affected finch beak size
- in a drought year, most food plants fail to produce seeds, except for a species that produces very large seeds
- birds w large, deep beaks have a better chance of survival than others
- offspring inherited these characters
what happened after the episode of severe drought in the Galapagos?
large, deep beaks were no longer favoured, and the populations evolved back towards the previous state
describe relation between or chips and pollinating moths
- for orchids, its important that a pollinating moth probes the flowers deeply, so that the polonium gets firmly attached to the moth’s head
- this ensures that the polonium makes good contact with the right part of the flower which the moth lists next to fertilise it
- this drives selection on nectary tube length (too short = nectar sucked without pollinia picked up, too long = waste nectar)
give an example of selection and counter-selection in humans
- resistance to malaria has involved changes in our red blood cells, where malaria parasites spend part of their complex life cycle
- leads sickle cell anaemia is usually fatal in the absence of medical treatment
how does the haemoglobin S (changed form) differ from haemoglobin A (normal form)
it is a variant form of the gene, and the two versions differ by a single DNA letter
what happens to individuals whose genes for haemoglobin are both the S type? and one?
- both: red blood cells become malformed and clog tiny blood vessels
- one: not affected but have benefit of higher resistance to malaria
the disease suffered by people with two S genes is a
cost of malaria resistance and prevents the S form from spreading throughout the population
variants of glucose-6-phosphate dehydrogenase as an adaptation of humans that give resistance to malaria
- variants of enzyme glucose-6-phosphate dehydrogenase; when people with these variants eat certain foods/drugs, their RBCs get damaged though the non-resistant version of the enzyme prevents this
blood type Duffy- as an adaptation of humans that give resistance to malaria
less susceptible to a certain type of malaria than people who carry the alternative Duffy+ type
what do malaria resistance variants show?
that different responses can occur to a single selective pressure
describe stabilising or purifying selection
- selection acts on every generation against mutant genes
- non-mutants tend to leave more offspring so their genes remain the most common
when does stabilising selection occur?
if the environment has remained fairly constant, so that selection in the past has had time to adjust a trait to the state which confers high fitness
how does stabilising selection make sense of the observation that species often show little evolutionary change?
as long as their environment poses non new challenges, selection will tend to keep things as they are
in what sex is sexual selection most prevalent?
males
cost of male characteristics due to sexual selection
lower survival
peacock males as an example of poor sexual selection
poor flyers due to big tails, and would probably be better able to escape predators if their tails were smaller
tropical frog species as an example of poor sexual selection
- they are preyed on by bats that detect males singing their courtships songs.
- expend large amounts of effort which could be employed for example in looking for food and are often in poor physical shape at the end of the mating season
Darwin considered selection in the context of courtship to be
different from most other situations
