Transcript in groups, partners can be found to harvest a resource or stalk large

Chapter 12
Life in Groups
In groups, potential mates are on hand; in groups,
partners can be found to harvest a resource or
stalk large prey
群體生活的價值與負擔
For many animals, the costs of group life are too
high, and life is lived mostly alone.
Who wins and who loses in a group is not easy to
determine. In fact, some biologists have argued
that the group
Alarm Calls
When danger threatens,
one or more members of the animal
group may give off a call,
These vocal calls are alarm calls that alert
others to the danger. From an evolutionary point
of view, alarm calls are a puzzling behavior. If
you have spotted an approaching predator, why
來吃我吧
call out and give away your position, thereby
drawing particular attention to yourself?
Vervet Monkey
A snake (e. g., python): low-amplitude;
looking at the ground
Stalking mammal (e. g., leopard ); a very loud, low-pitched
series of chirps; scatter for a secure sanctuary
Large bird (e. g., eagle); short, loud, staccato grunts
look up or just immediately beat a hasty retreat into dense,
covering vegetation,
If recorded tapes of the calls are played back, the
vervet monkeys respond in these same specific
and distinctive ways to each of the three types of
alarm call.
FIGURE 12.1 Alarm Calls
Belding’s ground squirrels of North America live in
burrows excavated themselves.
Predators threaten from the air, and from the
ground-coyotes, weasels, badgers, to name a few.
If the hawk more often catches a noncalling member
of the colony,
But if the terrestrial predator is successful, the caller
emitting the warning call is about twice as likely to
be caught as a noncaller.
One suggestion is that, in fact, individuals that
give alarm calls benefit directly from the
advantages of such a vocal warning.
The predator has been spotted;
Ready to make an effective escape,
sets colleagues all around into chaotic
pandemonium, confusing the predator,
Their few captures are usually the noncallers.
When responding to terrestrial predators, the
alarm caller actually may draw attention to itself,
increase its exposure and vulnerability, and fall
prey more often than its silent neighbors.
Such behavior is termed altruism, wherein an
individual’s trait or behavior reduces its own
relative chances of successful reproduction, but
this same trait or behavior enhances the relative
chances of others in its group to survive and
reproduce successfully.
Individual selection and Group selection
Altruistic behavior was linked with the idea that
group benefits outweigh individual advantages
犧牲小我；以大局為重
Some biologists saw selection acting at two
levels: one was individual selection, acting on
the particular phenotype of one organism, the
other group selection, acting on favorable traits
held in common by the group.
V. C. Wynne-Edwards entitled Animal
Dispersion in Relation to Social Behavior. The
book’s primary argument was based on the
observation that if we go out into nature, seldom
do we see animal populations actually
outstripping their resources. Certainly, animal
populations have the potential for astronomical
growth, but most populations seem to level off
and hold their numbers in check at sustainable
levels.
Wynne-Edwards argued, animals themselves
一名英藉女遊客於中國大陸內街上所攝，當時女嬰身體仍微暖，
sacrifice personal survival and fertility in order
但街上竟沒有人理會，只視她為垃圾。即後此名女遊客拍下了
to help control population growth- group
以下照片及通知公安處理，可惜救不回女嬰生命。其後公安拿
selection-based on altruistic behavior.
走了女遊客的底片，幸好公安拿走的是女遊客剛換上的底片，
如果不是如此，我們又怎可看到大陸的一胎制及重男輕女所帶
出的嚴重性。
• V.C. Wynne-Edwards
• Vero Copner Wynne-Edwards (4 July 1906 —
January 5 1997) was a British zoologist famous
for espousing group selectionist ideas which,
after the Williams revolution, are now generally
considered naive and incorrect. His son Hugh
Wynne-Edwards is a professor of geology, and
his granddaughter Kathy Wynne-Edwards a
professor of biology.
Wynne-Edwards, V.C. 1962. Animal Dispersion in
Relation to Social Behaviour. Edinburgh: Oliver
and Boyd.
Keyword: group selection.
Wynne-Edwards, V.C. 1963. Intergroup selection in
the evolution of social systems. Nature 200: 623.
Keywords: evolution of social systems • intergroup
selection.
Wynne-Edwards, V.C. 1986. Evolution Through
Group Selection. Oxford: Blackwell.
Keyword: group selection.
Altruism versus Selfish Behavior
With human ethical judgments: altruism-good;
selfish-bad. We are measuring animal behaviors
by human ethical codes, rather than by the stark
discipline of nature’s own rules,
Altruistic behavior, biologically speaking, is
characterized by loss of fitness by the giver to the
benefit of neighbors.
Selfish behavior is the opposite, gain for the giver
at the expense of neighbors.
Kin selection
group selection assumed that altruistic traits are
genetically based and thus transmissible to
future generations.
Inclusive fitness
Natural selection that favors actions benefiting offspring
and relatives is kin selection. It is a kind of individual
selection because individuals benefit-or, really, their
particular genotype benefits-through kin benefits.
The success, directly and indirectly, in promoting
one’s own genotype is inclusive fitness. 雞犬升天
六畜興旺
By promoting one’s own offspring, by funneling aid
to close relatives, or inclusively by doing a
combination of both.
Group Selection ?
Genetically speaking, parental care is very “selfish.”
Parents may exhaust themselves in rearing young
and expose themselves to threats when defending
their young offspring. 救火英雄
At one extreme, the female thwarts the predator’s
attack saving her young but she herself is killed.
The female bolts when a predator attacks-saving
herself and gaining the chance to breed again safely,
but losing all current offspring. 留得青山在
Certainly, many intermediate outcomes are possible
between these extremes.
FIGURE 12.3 Parental Care
下次多生幾個就好了 ??
Coefficient of relationship.
Expresses the degree or fraction of shared,
identical genes between two individuals
As a female’s offspring become more distantly
related, the proportion of the original female’s
genotype in each becomes less and less,
gradually diminishing 孔老夫子 第 n 代孫 (2n)
two brothers
for eight first cousins.
所屬網頁 http://www.zoo.cam.ac.uk/zoostaff/
The trespassing cuckoo female may actually
pitch out the eggs of the host, leaving only her
own eggs
Further, cuckoo chicks often hatch first, grow
rapidly, and if any host nestlings still remain, the
cuckoo chicks may muscle them out of the nest,
build nests in concealed locations,
attack the brood parasite female
detect the distinctive eggs of the brood parasite
and evict them.
巨嬰
FIGURE 12.4
Brood Parasite
邀受 !
So Big
The large young cuckoo (right) has evicted the smaller
young of the host meadow pipit (left) and begs for food.
Levels of Selection
Richard Dawkins argues that selection acts
directly on DNA,
Serious attempts have been mounted to find
mechanisms by which group characteristics
prevail over individual fitness--group selection.
Individuals engaged in behaviors producing
successful propagation of individual genotypes
into future generations have higher fitness than
those not practicing such advantageous
behavior. This is kin selection.
• Natural selection favoring the spread of allels
that increase the indirect component are the
result of kin selection
Microevolution is the
evolutionary event
concerned with patterns of
change within a population
or species.
Macroevolution is an
evolutionary event the
origin of species and
higher-level taxa.
注定
宿命絕後
六畜興旺
FIGURE 6.5 Morphological
Series
Fig. 24.24
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Macroevolution has been largely the province of
paleontologists, who take a longer view of
events unfolding through geologic time.
Paleontologists recognized that species appear
“abruptly” in the fossil record, persist for a long
time often with no apparent change, then just as
“abruptly” disappear.
所屬網頁 http://www.wfdn.com.tw/9203/030315
FIGURE 12.5
Macroevolution and
Microevolution
G. G. Simpson insisted that, this capricious
pattern was genuine, a reflection of a common
feature of evolution itself.
He termed such sudden appearance, often of
major new groups, quantum evolution. Simpson
eventually
this pattern to the same
Geneticistsattributed
invoked”mutationism”
culling mechanisms as are behind
microevolution,
thattothey
were speeded
Some biologistsexcept
returned
Lamarck
up during these short bursts of rapid change,
summing
up to
macroevolutionary
Evolutionary
change
was driven bychanges.
internal
engines
•
FIGURE 12.6 Quantum
Within taeniodonts, a group of extinct placental
Evolution
mammals, two lineages
evolved. One was the
original group of taeniodonts, the conoryctines
that survived into the late Paleocene; the other
lineage was the stylinodonts, which evolved
rapidly (quantum evolution) across a transition to
a new adaptive zone (lifestyle). Compared to the
beaver-sized conoryctines, the bear-sized
stylinodonts evolved specialized dentition
especially suited to rough and highly abrasive
foods, well-developed claws, and strong
muscles suggesting a digging foraging style.
(After Simpson 1953.)
Pace of macroevolution
Punctuated
equilibrium
Phyletic
evolution
In the early 1970s, two biologists, Niles
Eldredge and Stephen Jay Gould, returned to
the issue of saltational events and rates of
change in the fossil record raised several
decades earlier by simpson. They coined the
term punctuated equilibrium
A species persisted, more or less unchanged, for
long periods which then were suddenly, in 不變則已
geological terms, punctuated by rapid change.
This was punctuated equilibrium--long periods of
little change (equilibrium) interrupted (punctuated)
by sudden change. The punctuated moment is
marked by speciation, thereby producing new
lineages
or, technically,
hence,
the pattern
Steven Stanley:
speciesclades;
become
“individuals”
and
is
known asand
cladogenesis.
This iswith
in contrast
to
speciation
extinction equate
birth and
phyletic
evolution (anagenesis)
death, respectively.
Species selection.
難以想像的 Group selection….只好認了
No clear -–cut, unambiguous examples in nature.
Lack of such examples diminishes its plausibility.
It is hard to imagine what the selective agent
might be,
no evidence exists for selective agents acting at
higher levels of organization
Microevolution and macroevolution remain
coupled.
Rapid evolution
The context of punctuated equilibrium was over
pattern (caldogenesis versus anagenesis) and
process (species selection versus individual
selection), but it also renewed interest in rates of
change-rapid versus gradual changes.
For Simpson, quantum evolution was phyletic
evolution speeded up, propelling a species from
one adaptive zone to another, quickly crossing a
transitional zone between.
FIGURE 12.8 Cladogenesis, Details
On the edge
It often produces many fragmented and isolated
groups out of the original, single population.
Because isolated groups are smaller,
This gives rare features a presence, denied
within the larger population, and in a sense
these characteristics are “seen” and “saved”
locally by natural selection.
Populations may be fragments, on the margins
of the major species range--peripheral isolates.
FIGURE 12.9 Peripheral Isolates
Genetic drift
Many peripheral isolates are populations
at the extremes of a species’ geographic
range; Meet extreme conditions,
Mortality may be high and population size
fluctuates dramatically. In small
populations, chance alone may
determine which individuals survive.
founder effect; bottleneck effect
Genetic drift—bottleneck effect,
in theory
• In a large collection of individuals, here the
blue and yellow marbles, approximately
equal numbers of both are present.
However, when just a few persist to start
the next generation, chance alone may
yield mostly blue. Because most are blue,
the next generation, even if large numbers
are produced, are now mostly blue.
In small, isolated populations, chance events
can wipe out a whole population. Disease, crash
of the food supply, drought, or floods
First, most new species likely appear on the
margins of a geographic range where the small
numbers of the new species are unlikely to leave
significant fossil evidence of its occurrence and
transitional changes.
Second the displacement of the ancestral species
by the new species is rapid and, in the more
protracted fossil record, appears as a “gap”
between species.
An evolving lineage produces distinct species
through time, A-H. Each species arises in
isolated populations, under the chance and
selective events just described, then spreads,
occupying an expanded geographic range of its
own.
The fossil record would look as if
discontinuities--gaps--occurred between
species.
Suppose, for example, that
the only geological location
available for exploration is
restricted to Location 1, a
narrow cross-section back
through time. We might find
remains of species A, B, C,
and maybe D, but not any
others until we reach G.
Macro Changes at Micro Levels
Flight came later in birds. Immediate ancestors
to birds were ground- or tree-dwelling,
reptilelike animals.
Preadaptation, meaning that a structure or
behavior possesses the necessary form and
function before being remodeled into a new role
it later serves.
一構造或行為已具有另一新適應特性的功能及雛型
Macro Changes at Micro Levels
Feathers did not evolve at one time for service
millions of years later in flight. They evolved
initially for their advantages of the moment
(insulation) not for their role in the distant future
(flight).
Vertebrate jaws; legs evolved from fins; penguin
flippers evolved from wings of ancestors;
dolphin fins evolved from legs
Embryonic changes
Another way to produce rapid changes is
through major adjustments during embryonic
development, based on genetic mutations that
affect embryology. Lizards are reptiles, and
some lizard species are legless.
Fig. 24.22
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
In lizards with limbs, an early embryonic gathering of
cells called a somite grows downward along the sides of
the embryo at sites where fore- and hindlimbs are to
form. Here, the somite’s lower growing tip meets special
cells-mesenchymal cells, they initiate a “limb bud”.
In legless lizards,
lower tip of the somite fails to grow downward into the
area of the prospective limb.
In the environment the limbless young realized some
competitive advantages (sleekness) over others with
limbs (obstructions), and survived.
Hox genes regulate the appearance of major body
parts, such as body regions, legs, antennae, and
wings.
In snakes, the Hox genes that regulate
forelimb development have deactivated
normal forelimb development, leading the
absence of forelimbs.
Evolutionary significance
Such large-scale change
single gene mutation
A hundred gene mutations
the relatively few
First, group selection includes no plausible culling
mechanism, no selective agent that “sees” or acts
directly upon group traits.
Second, most supposed cases of group selection
observed in nature, in fact, when closely studied,
collapse down to a special case of individual selectionkin selection.
G. G. Simpson was one of the first to recognize that
these saltational events between groups represented
not an artifact of preservation.
Individuals in small, isolated populations experience
extreme conditions.
Preadaptation is the evolutionary process
wherein ancestral structures come to serve in
new ways
Master control genes- Hox genes- control banks
of genes that in turn manage the assembly of
an organism.