chapter 8 Flashcards
what fossil evidence is needed to support humans evolving from apes?
fossil of a missing link between humans and apes/chimps shld be found
what is a missing link?
ancestral species which split/speciated(?) to give rise to two diff species
why is finding the specific missing link responsible for humans and chimps unrealistic?
identifying it wld require a complete set of ancestor-desendant fossils in both chimp and human lineage all the way back to when the lineage split which is unrealistic to have
why are fossils of human ancestors difficult to find?
human ancestors were few in number and inhabited a dry part of africa which is not good for fossilization
rather than a direct missing link, what else can link human and chimps together?
fossils of evolutionary cousins of the missing link
what might the missing link b/w humans and chimps look like and why?
the common ancestor/missing link b/w humans and chimps was diff than both humans and chimps, but most likely more closely ressembled chimps as most modern apes do
ex. gorillas are distant cousings to humans and chimps, but share many features w/ chimps, whilst humans have many unique features other modern apes do not have
how do humans differ from other modern apes?
ex. relatively small brains, hairiness, other modern apes have knuckle walking, pointed canine teeth, rectangular dental arcade (bottom row teeth look like 3 sided rectangle)
in contrast humans have uniquely flexible thumbs, little hair, smaller/blunter canine teeth, walk erect, parabolic tooth row, relatively larger brain
how can ppl tell whether something walked upright from just a skull?
for knuckle walkers (ex. gorillas, chimps) posture is horizontal and spinal cord enters through skull’s rear
for erect walked (humans) skull is directly atop spinal cord and hole is set farther forwars, which is demoed in sahelanthropus
what human trait was first to evolve in human ancestors and why do we think this?
most likely bipedal walking evolved first
schelanthropus tchadenis which is the oldest discovered entry of a hominin/human ancestor demonstrates traits which show bipedal walking
what were some traits changes which occured as time passed and human ancestors evolved to reassemble modern humans?
progression of the parabolic tooth row, enlarging brain, skeleton losing apelike features
what is special abt the h. erectus?
it hold the disintcion of being the first hominin to leave africa
what is the multiregional theory and why is it supported?
proposes h. erectus (maybe h. neanderthalensis too) evolved into h. sapiens independently in several areas, perhaps natural selection was acting in the same way in asia, europe and africa (convergent evolution?)
this might be due to significance of race, multiregional hypothesis w/ splitting of pops millions of years ago predicts 15 times more genetic diff b/w race than if humans left africa only 60 000 yrs ago
what is the out of africa theory and why is it supported?
it proposes h. sapiens originated in africa and spread physically replacing h. erectus and neanderthals bt outcompeting them for food/killing them
genetic evidence supports out of africa theory, however there is still dispute
what is the overall timeline of human-chimp divergence?
from connecting all fossils/species we have found, its known that divergence of human ancestors and chimps happened in east/central africa abt 7 million yrs ago
what are two theories as why humans evolved to be hairless?
humans may have evoled to be hairless due to increased sweat glands as hair inteferes w/ cooling evaporation of sweat
aquatic ape theory argues early hominins spent a large amount of time foraging in water, erect posture is a result of needing to keep head above surface
what is classic adaptive theory and what is evidence which supports it?
classic adaptive theory is that bipedal walking freed hands to do other things like make tools which lead to selection for bigger brains to allow for thinking up more complex tools
supported by the fact first tool appeared arnd the same time as beginning of brain enlarging, but ignores other potential selection pressure like language development, pyschological intricacies ofnprimitive society, planning
what are humanness genes?
humanness genes are an attempt to find out what genes make use so diff from other aps
humans and chimps differ by 1.5% in protein sequences, is this a lot?
however 1.5% diff in protein sequences is actually a lot of diff, it means for there will be an average of 1 diff in 100 amino acids, proteins are made of hundreds of amiono acids so 1.5 diff wld mean in a protein 3 hundred amino acids long means there will be on average 4 diffs in the total protein sequence
analogy, changing 1 perent of leters on a page will alter more than 1 percent of sentences
since proteins are essential for building + maintaining bodies, a single diff can create v large diffs
how do human and chimp diverge in terms of genes?
humanness/human’s genetic divergence from chimps relies on proteins produced by genes, absences of genes, number of gene copies, time gene is expressing during development
how do human and chimp diverge in terms of genes?
humanness/human’s genetic divergence from chimps relies on proteins produced by genes, absences of genes, number of gene copies, time gene is expressing during development
how does genetic variation in human correlate w/ physical traits?
genetic variation found by molecular techniques weakly correlated w/ physical traits like skin colour, hair type used to determine race
how does genetic variation correlate w/ human races?
genetic evidence shows 10-15 percent of genetic variation is represented by diff b/w race which can be physically recognized, remaining 85-90 percent genetic variation occurs among individuals within a race
this means races don’t carry completely diff genes/alleles, rather ppl have the same alleles w/ diff frequencies
why is knowing ancestry and allele frequency useful for humans?
knowing ancestry is useful for diagnosing genetically based diseases, and knowing diff allele frequencies in diff races means finding appropriate organ donors shld take race into account
what aspect of humans which other species might not share might influence genetic changes the fastest?
humans can change culture, much faster than they can evolve genetically and this can produce genetic changes
this is known as gene-culture evolution and its suggestds that cultural enviro leads to new selection types on genes which supports the idea that phys diff of races resulted from sexual selection
