comparative anatomy

fossil evidence and current observations can provide…

information about the anatomy of organisms, allowing scientists to compare the structural features of related animals to ascertain degree of similarity between them.

similarities often suggest…

a common ancestor

what are the three areas looked at in comparative anatomy?

comparative embryology, homologous organs/ structures, and vestigial organs/ structures.

what is comparative embryology?

is c comparing the very early stages of embryonic development. it provides evidence of common ancestry and evolutionary. change over time

what is comparative homologous organs/ structures?

is the study o f organs that are a similar strucutre but may be used/ adapted for different conditions

what is comparative vestigial organs/ structures?

is the study of organs that may have once been important but have lost or changed their function

comparative embryology is usually undertaken in..

vertebrates (posses a backbone, and a skull)

embryos are initially very similar between species until…

differentiation occurs during development.

in embryology, more closely related species are…

similar for a longer period of time (this is evidence of relatedness)

at one point in development what do chickens and humans have in common?

they both have slits and arches in their neck these are similar to the gil slits and arches in fish , but they do not develop into grills (their similarities indicate a common ancestor)

in human embryos, they have gill slits and arches in their necks, what does this develop into

one gill sit becomes the Eustachian tube (connects eat to throat), the tissues from around the gills develops the thyroid and the tonsils (this indicates common ancestry then adaptation (reflected in embryonic development))

what are some common features in vertebrae embryos?

tail, a two chambered heart, similar brain development, gills

what are homologous structures?

they are structures that are the same across species but adapted for different functions. e.g the same bones appear in a variety of different species, but they are used for different function, this is evidence for common ancestry, then adaption

what is an example of homologous structures?

forelimbs in vertebrates, (the feet of amphibians and reptiles, wings of bats and birds, leg of a horse, flipper of whale/ seal, human hand)

why are the forelimbs of vertebrates homologous structures?

in every case the bones are arranged in a similar way i.e a similar structure (even though they have developed different functions e.g swimming, flying, walking, human hand things 🤷‍♀) this arrangement of bones on the forelimb in such a range of vertebrates is convincing evidence that they all have evolved from a common ancestor

organisms possessing homologous structures are likely to have…

a common ancestor

what are anthropoids?

human like primates (e.g great apes and humans)

link anthropoids ad homologous structures.

they show many anatomical resemblances. High degree of traits are shared and similarity especially considering range of habitats. this shows that these two species share a common ancestor and therefore are closely related, showing that evolutionary divergence is relatively recent

what are vestigial structures?

they are structures that have changed during evolution to the point they no longer fulfil their original function. they have no/ limited use in organism, but were of use in ancestral form (now usually smaller or absent)

vestigial organs/ structures are common in…

vertebrae species (humans have approx 90 of these structures)

vestigial structures are largely to entirely…

functionless when their original roe is being considered (they may retain a lesser function or develop a new one)

vestigial organs show evidence that…

the organism have evolved from an ancestor but these organs have ceased to be useful and are no longer selected for

list osme vistigal structures in humans

appendix, nictitating membrane, wisdom teeth, males nipples, muscles at the base of hairs, vertebrae for tail, muscles that lie above the public bone (pyramidallis muscles)

what is the nectitating membrane (or transparent 3rd eyelid)?

is found in cats, birds, frogs to cover their eye for protection

why is the nictitating membrane a vistegial organ in humans?

it is the pinkish membrane located in th corner of the inner eye, it is unable to cover the whole eye like it does for protection in other animals therefore it cannot fulfil its original function (but does have some use in tear drainage)

why are wisdom teeth vestigial?

they erupt abnormally, and cannot be used in mastication. 1/5 of population do not have them

why is the coccyx vestigial in humans?

the vertebrae for the tail is fused to form the coccyx

why are the muscles that lie above the public bone vestigial?

only 1/5 of the population do develop these muscles (if they are present they do not change/ enhance muscle performance)

why are male nipples deemed vestigial?

(some would say they are not vestigial as they never had. any function in the first place)

why do males have nipples?

they have appeared to retain in males because all human foetuses develop from the same base genetic form (and as female nipples have an important function, males have them)

why are the muscles at the base of hairs vestigial?

these are used in mammals with fur/ spines and birds with feathers, these tiny muscles pul the hair or feather upright. this creates a layer of insulating air to protect against the cold. However in humans the hair is so fine it is not capable of this function and this contraction of muscles is goosebumps

why are appendixes vestigial?

with the change of diets from more herbivorous to make it more easy to digest food (from the meat) therefore the appendix is no longer needed for its original function. many humans have their appendixes removed following inflammation (appendicitis) there does not appear to have any negative affects of the removal.

what role does an appendix have in herbivorous vertebrates?

plays a role in digesting tough plant matter. thought that it played a similar roe in ancient humans (whose diet was more herbivorous)

what do scientists think the appendix does now?

indicating the appendix actually has a role in the immune system, and that it produces and stores good gut bacteria.

will vestigial organs slowly disappear?

such organs will probably disappear together as there is no selection pressure for them

what is a selection pressure?

an evolutionary force that causes a particular phenotype to be more favorable in certain environmental conditions.

how does an organ become vestigial?

with changing environmental conditions, such organs become no longer essential to survive and were gradually reduced to vestigial remnants. these remnants are not harmful in any way therfore they have not been completely eliminated.

why do some people not have vestigial organs (e.g wisdom teeth)?

natural selection has reduced organs to non- functional remains because it would. be a waste of the organisms energy and resources to maintain useless structures

why does geographical distribution support evidence for evolution?

it can show plausible link between a common ancestor, and clusters of related species in the same geographical location.

what is the example of geographical distribution in humans?

as humans most resemble chimpanzees and gorillas. therefore we can infer and hypothesise that the common ancestor of great apes and humans are most likely lived where the chimps and gorillas are (Africa) rather where the lemurs or new world monkeys are. this has been shown true as there was been discovery of ancestral fossils in African rift valley.

explain how geographical distribution impacted the way that Darwins finches looked like.

On the Galápagos Islands, finches on different Islands were different to the finches on South American Mainlands. because there was seperate islands, there was no competition, to they evolved to take advantage of food sources on the different islands. therfore the beaks adapted to the different food sources. eventually they evolved into 13 seperate species on the islands, (evidence of species on island evolving from a common mainland ancestor)