In groups, potential mates are on hand; in groups, partners can be found to harvest a resource or stalk large prey

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

Chapter 12 Life in Groups

群體生活的價值與負擔

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 call out and give away your position, thereby drawing particular attention to yourself?

Alarm Calls

來吃我吧

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 gruntslook 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.

Vervet Monkey

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.

Altruistic behavior was linked with the idea that group benefits outweigh individual advantages

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.

Individual selection and Group selection

犧牲小我；以大局為重

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 sacrifice personal survival and fertility in order to help control population growth- group selection-based on altruistic behavior.

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， 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.

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.

Altruism versus Selfish Behavior

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.

By promoting one’s own offspring, by funneling aid to close relatives, or inclusively by doing a combination of both.

雞犬升天六畜興旺

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.

Certainly, many intermediate outcomes are possible between these extremes.

留得青山在

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, graduall

y diminishing 孔老夫子 第 n 代孫 (2n)

two brothersfor 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.

FIGURE 12.4 Brood Parasite

The large young cuckoo (right) has evicted the smaller young of the host meadow pipit (left) and begs for food.

邀受 !So Big

巨嬰

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.

Levels of 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

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 24.24

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 attributed this pattern to the same culling mechanisms as are behind microevolution, except that they were speeded up during these short bursts of rapid change, summing up to macroevolutionary changes.

Geneticists invoked”mutationism”

Some biologists returned to Lamarck

Evolutionary change was driven by internal engines

FIGURE 12.6 Quantum Evolution • Within taeniodonts, a group of extinct placental

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 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, clades; hence, the pattern is known as cladogenesis. This is in contrast to phyletic evolution (anagenesis)

Steven Stanley: species become “individuals” and speciation and extinction equate with birth and death, respectively. Species selection.

不變則已

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.

難以想像的 Group selection…. 只好認了

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.

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.

Macro Changes at Micro Levels

一構造或行為已具有另一新適應特性的功能及雛型

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

Macro Changes at Micro Levels

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.

Embryonic changes

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Fig. 24.22

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 changesingle gene mutation

A hundred gene mutationsthe 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 selection- kin 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.