The Ancestor The Ancestor's Tale

18 Pages·2006·2.43 MB·English

IIaann GGiiddddyy//TThhee AAnncceessttoorr’’ss TTaallee 11
TTTThhhheeee AAAAnnnncccceeeessssttttoooorrrr’’’’ssss TTTTaaaalllleeee
AAnn eexxpplloorraattiioonn ooff oouurr aanncceessttoorrss……tthhee ppaasstt 33..55 bbiilllliioonn yyeeaarrss
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TThhee tteenneettss ooff eevvoolluuttiioonnaarryy tthheeoorryy
(cid:1) More are born than can
possibly survive –the
Malthusian imperative.
(cid:1) Random mutations
sometimes produce adaptive
survival traits –ega beak
that is better able to crack
seeds. These are passed on
in a higher proportion than
nonadaptivecharacters.
(cid:1) Adaptation under
segregation –egislands,
mountain ridges –produces
mutually infertile groups –
new species.
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SSeeeekkiinngg oouurr nneeaarreesstt ccoommmmoonn aanncceessttoorr……
(cid:1) Every two species has at least one
common ancestor.
(cid:1) We are not descended from the apes; we
are just different kinds of apes. We and
other primates such as snow monkeys
(right) are both descended from another
kind of primate. We and chimps, we and
birds, each share a single “nearest
common ancestor.”
(cid:1) Every form of life, present and past,
evolved from common ancestors, all the
way back to the first form of bacterial life,
3.5-4 billion years ago.
(cid:1) This is known because every known form
of life shares the same genetic language,
DNA, with only 4 “letters” (the bases A, C,
G, T), from which is constructed the
instruction set (genetic code) for the
assembly of our bodies.
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TThhee tthheemmee:: wwhhoo wweerree oouurr ““mmoosstt rreecceenntt ccoommmmoonn aanncceessttoorrss??””
(cid:1) Phylogenetictrees, illustrated here by
Darwin’s original sketch, reveal
evolutionary histories: each "fork in the
road," or branching point, indicates a
common ancestor splitting into two
descendants.
(cid:1) The fewer branching points there are
between any two species, the more closely
they are related—a feature that has great
predictive value. Example: a botanist who
discovers a useful pharmacological
property in one plant species might
investigate "sister" species for similar
properties.
(cid:1) Cladisticsis the science of refining this
“tree of life” using the tools of paleontology,
geology and genetics.
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TThhee TToooollss::
FFoossssiillss,, RRoocckkss aanndd DDNNAA
(cid:1) Scientists employ shared anatomical
featuresto determine evolutionary
relationships. Fossils, along with half-life
rock dating, help determine the timing of
anatomical changes.
(cid:1) More recently, they have learned that the
history of evolution is also recorded in
DNA,the set of instructions for building
bodies encoded in all living cells. When
plants and animals reproduce, they pass
copies of their DNA on to their offspring.
(cid:1) Over time, the DNA of a species changes,
usually as a result of copying errors
(mutations). Scientists can compare DNA
to help discover evolutionary linkages: in
general, the greater the difference in DNA
between two species, the more time must
have passed since the two groups were
one, since they diverged from a common
ancestor.
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YYoouu oolldd ffoossssiill
(cid:1) Fossils –shapes imprinted in
rocks –tell stories of ancient
organisms’ structures. Taken in
the context of rocks and
chemicals, we can learn their
ecology and adaptations.
(cid:1) The earliest bacterial fossils date
back to 3.5 billionyears ago.
(cid:1) The famous fossil at right is
Archaeopteryx, whose discovery
helped us to learn that birds are
descended from the dinosaurs.
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DDaattiinngg aa rroocckk ssttaarr
(cid:1) Successive layers have long been distinguished by their
fossils, but today’s geologists use half-life dating.
(cid:1) Many elements, such as carbon and hydrogen, have
radioactive (decaying) variants called isotopes. The decay
converts them into another isotope or element. The probable
time for half of a given quantity of such an isotope to convert
is its half life. a
(cid:1) Different isotopes have vastly different half lives–and this is
Volcanic
what enables dating, For example:
Ar40:K40=0.25:1
Half of Decays to in
Sedimentary
Carbon 14 Nitrogen 14 5,730 years
Sedimentary
Potassium 40 Argon 40 1.3b years
Uranium 236 Lead 206 4.5b years
(cid:1) Example: if there is 2x as much argon
Volcanic
40 as potassium 40, the rock crystal is
2.6 billion years old. Ar40:K40=0.3:1
(cid:1) How old is the coelacanth?
Ian H Giddy aym 093 dna 523 neewteb :rewsnA 9
TThhee DDoouubbllee HHeelliixx
(cid:1) The history of our evolution is recorded in
each person’s DNA. Our unique human
DNA “instruction set” is like a computer
program employing a limited set of
subroutinesin a programming language
common to all known forms of life.
(cid:1) The 4 “letters” spell 64 “words” (codons). A
“sentence” of codonsspecifying a particular
protein molecule is called a gene.
(cid:1) Each human cell contains about 30,000
genes. Most strings of our DNA are
meaningless or unused, like early drafts of a
program on a cluttered hard disk. “Everything about a plant or animal,
including its bodily form, its inherited
(cid:1) These useful subroutines and early
behavior, and the chemistry of its cells, is a
versions, which we have in common with coded message about the worlds in which
most other living organisms, record the story its ancestors survived; the food they sought;
of our kinship and evolution. the predators they escaped; the climates
they endured; the mates they beguiled.
(cid:1) The DNA instruction set has been passed The message is ultimately scripted in the
on, with minor random changes, from DNA that fell through the succession of
generation to generation, for almost four sieves that is natural selection.” (Dawkins)
billion years.
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DDeettaaiillss
Each species experiences one base
change per 25 million years
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FFrroomm DDNNAA ttoo aa pphhyyllooggrraamm
(cid:1) Organisms’“characters”
including DNA similarities
help form groupings –but
whichgroupings to avert
superfluous matches?
(cid:1) The goal is to describe
evolutionary paths.
(cid:1) Among other methods,
Bayesian maximum
likelihood analysisseem to
work well.
(cid:1) Much debate prevails–
especially as to how to
organize the early groups.
Source: AMNH
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OOff RRaattss aanndd MMeenn
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LLeett’’ss ssttaarrtt oouurr jjoouurrnneeyy,, aanndd mmeeeett tthhee ffiirrsstt hhuummaannss
(cid:1) Mitochondrial
DNA is a section Out of Africa,
of DNA so tightly
again and again
bound that it
travels through
history as a single
unit
(cid:1) mDNA, carried
exclusively
through the
female line, lets
us trace the most
recent female Mitochondrial Eve, 140,000ya
ancestor of all
living humans.
(cid:1) Other DNA Homo erectus, 1.7mya
groups, too, help
tell the Ancestor’s
Tale
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Out of Africa,
again and again
WWee mmeeeett ppeeooppllee wwee’’llll nneevveerr mmeeeett
(cid:1) Neanderthal manis
closely related to Homo sapiens
our species, Homo
sapiens.
(cid:1) But fossil evidence Homo
finds no trace of neanderthalis ☺mEve
any of their
descendents, and
newly discovered
Neanderthal mDNA
strings are quite
distinct from those Human-
of all surviving Neanderthal
humans. common
ancestor, 0.5mya
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OOtthheerrss wwhhoomm wwee’’llll mmeeeett oonn tthhee vvooyyaaggee bbaacckk iinnttoo ttiimmee
(cid:1) African ape-
men
63 mya
(cid:1) Chimpanzees
(cid:1) Gorillas The great
Cretaceous
(cid:1) Orang utans catastrophe
(cid:1) Gibbons
(cid:1) Old world
monkeys
(cid:1) New world Transition to
monkeys primates
(cid:1) Tarsiers
(cid:1) Lemurs
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WWhhoomm wwee’’llll mmeeeett oonn tthhee vvooyyaaggee bbaacckk iinnttoo ttiimmee
(cid:1) Tree shrews
(cid:1) Rodents
(cid:1) Laurasiatheres
180 mya
(cid:1) Xenarthrans
(cid:1) Afrotheres
(cid:1) Marsupials
(cid:1) Monotremes
Transition to
mammals
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WWhhoomm wwee’’llll mmeeeett oonn tthhee vvooyyaaggee bbaacckk iinnttoo ttiimmee
(cid:1) Sauropsids
(cid:1) Amphibians
(cid:1) Lungfish
(cid:1) Coelacanths
(cid:1) Ray-finned fish
(cid:1) Sharks
(cid:1) Lampreys
530 mya
Transition to
vertebrates
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WWhhoomm wwee’’llll mmeeeett oonn tthhee vvooyyaaggee bbaacckk iinnttoo ttiimmee
(cid:1) Lancelets
(cid:1) Sea squirts
(cid:1) Ambulacrarians
(cid:1) Protostomes
(cid:1) Cnidarians
(cid:1) Placozoans
(cid:1) Sponges
Transition to
multicellular
animals
800 mya
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WWhhoomm wwee’’llll mmeeeett oonn tthhee vvooyyaaggee bbaacckk iinnttoo ttiimmee
(cid:1) Choanoflagellates
(cid:1) DRIPs
(cid:1) Fungi
(cid:1) Amoebazoans
(cid:1) Plants
(cid:1) Uncertain clades
(cid:1) Archaea
(cid:1) Eubacteria
Transition to eukaryotes
(nucleated cellular
organisms)
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PPiillggrriimmss’’ ssttoorriieess:: jjooiinniinngg tthhee BBoonnoobbooss
(cid:1) African ape-
Chimpanzees and bonobosare
men qCuhiteim upnalinkeze ine st haenird b beohnaovbioors. Yaeret
quite unlike in their behavior. Yet
they have a common ancestor, and
(cid:1) Chimpanzees aanndd BBoonnoobbooss tothgeeyt hhearv teh eay c sohmarme oan M aonsct eRsetcoer, natn d
together they share a Most Recent
Common Ancestorwith us.
(cid:1) Gorillas Common Ancestorwith us.
MRCA date: about 6 mya
MRCA date: about 6 mya
(cid:1) Orang utans MMRRCCAA p plalaccee: :A Afrfircicaa
MRCA features: like a chimpanzee;
(cid:1) Gibbons hMaiRryC; Aw afelkaetdur oens: hlikaen ad schimpanzee;
hairy; walked on hands
(cid:1) Old world
monkeys Hominids Chimpanzees Bonobos
(us)
(cid:1) New world
monkeys
(cid:1) Tarsiers
(cid:1) Lemurs MRCA
(Most recent common ancestor)
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PPiillggrriimmss’’ ssttoorriieess:: jjooiinniinngg tthhee NNeeww WWoorrlldd MMoonnkkeeyyss
(cid:1) African ape- New world monkeys, with flat noses, are descended
New world monkeys, with flat noses, are descended
men frforomm A Afrfircicaanns s– –ththeeyy p prorobbaabblyly r araftfetedd t oto S Soouuthth
America. They have prehensile tails, and like most
America. They have prehensile tails, and like most
(cid:1) Chimpanzees mmaammmmaalsl,s ,t htheeyy a arere c coololorbrblinlindd ( d(dicichhrorommaatitcic).) .A Appees s
and old world monkeys rediscovered color
and old world monkeys rediscovered color
(cid:1) Gorillas (trichromatic), and so did howler monkeys, but in a
(trichromatic), and so did howler monkeys, but in a
completely differentway.
(cid:1) Orang utans McRoCmAp dleatetely: daibffoeuret n4t0w mayya.
MRCA date: about 40 mya
(cid:1) Gibbons MMRRCCAA p plalaccee: :A Afrfircicaa
MRCA features: like a monkey; dichromatic
MRCA features: like a monkey; dichromatic
(cid:1) Old world
monkeys
Apes(us) Tamarins
(cid:1) New world Night owls
Tatis
monkeys
Howlers & spiders
(cid:1) Tarsiers
(cid:1) Lemurs
MRCA
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