In groups, potential mates are on hand; in groups, partners ...
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 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 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 a nd distinctive ways to each of the three types of al arm call. FIGURE 12.1 Alarm Calls
Beldings ground squirrels of North America live in b urrows excavated themselves. Predators threaten from the air, and from the groun d-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 b e caught as a noncaller. One suggestion is that, in fact, individuals that g ive alarm calls benefit directly from the advanta ges of such a vocal warning. The predator has been spotted; Ready to make an effective escape,
sets colleagues all around into chaotic pandem onium, 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 individuals 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 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 books 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.
V.C. Wynne-Edwards Vero Copner Wynne-Edwards (4 July 1906 January 5 1997) was a British zoologist famous f or espousing group selectionist ideas which, afte r the Williams revolution, are now generally cons idered naive and incorrect. His son Hugh Wynn e-Edwards is a professor of geology, and his gra
nddaughter Kathy Wynne-Edwards a professor o f biology. Wynne-Edwards, V.C. 1962. Animal Dispersion in Re lation to Social Behaviour. Edinburgh: Oliver and B oyd. Keyword: group selection. Wynne-Edwards, V.C. 1963. Intergroup selection in t
he evolution of social systems. Nature 200: 623. Keywords: evolution of social systems intergroup selection. Wynne-Edwards, V.C. 1986. Evolution Through Grou p 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 natures 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 ones own genotype is inclusive fitness.
By promoting ones 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 a
nd expose themselves to threats when defending the ir young offspring. At one extreme, the female thwarts the predators att ack saving her young but she herself is killed. The female bolts when a predator attacks-saving her self and gaining the chance to breed again safely, bu t losing all current offspring. Certainly, many intermediate outcomes are possible
between these extremes. FIGURE 12.3 Parental Care ?? Coefficient of relationship. Expresses the degree or fraction of shared, ide
ntical genes between two individuals As a females offspring become more distantly r elated, the proportion of the original females ge notype in each becomes less and less, graduall y diminishing n (2n) two brothers for eight first cousins.
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
! 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 r esult of kin selection Microevolution is the evol utionary event
concerned with patterns of change within a population or species. Macroevolution is an evol utionary event the origin of species and higher-level ta xa.
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. http://www.wfdn.com.tw/9203/030315 FIGURE 12.5 Macroevolution and
Microevolution G. G. Simpson insisted that, this capricious pat tern was genuine, a reflection of a common feat ure of evolution itself. He termed such sudden appearance, often of m ajor new groups, quantum evolution. Simpson e ventually
attributed this pattern to the same culli Geneticists invokedmutationism ng mechanisms as are behind microevolution, e xcept they were speeded
up during these s Somethat biologists returned to Lamarck hort bursts of rapid change, summing up to mac roevolutionary changes.
Evolutionary change was driven by internal engin es FIGURE 12.6 Quantum Within taeniodonts, a group of extinct placental
Evolution mammals, two lineages evolved. One was the or iginal group of taeniodonts, the conoryctines that survived into the late Paleocene; the other lineag e was the stylinodonts, which evolved rapidly (qu antum evolution) across a transition to a new ad
aptive zone (lifestyle). Compared to the beaver-s ized conoryctines, the bear-sized stylinodonts ev olved specialized dentition especially suited to ro ugh and highly abrasive foods, well-developed cl aws, and strong muscles suggesting a digging fo raging style. (After Simpson 1953.) Pace of macroevolution
Punctuated equilibrium Phyletic e volution In the early 1970s, two biologists, Niles Eldredg
e and Stephen Jay Gould, returned to the issue of saltational events and rates of change in the f ossil record raised several decades earlier by si mpson. They coined the term punctuated equili brium A species persisted, more or less unchanged, for l ong periods which then were suddenly, in geologic
al terms, punctuated by rapid change. This was pu nctuated equilibrium--long periods of little change (equilibrium) interrupted (punctuated) by sudden c hange. The punctuated moment is marked by spec iation, thereby producing new lineages or, technica lly, clades; hence,
the pattern is known as cladoge Steven Stanley: species become individuals
and nesis. Thisand is inextinction contrast to phyletic evolution speciation equate
with birth and(ana dea th, respectively. Species selection. genesis) Group selection.
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 p attern (caldogenesis versus anagenesis) and proc ess (species selection versus individual selection), but it also renewed interest in rates of change-rapi d versus gradual changes. For Simpson, quantum evolution was phyletic evol
ution speeded up, propelling a species from one a daptive zone to another, quickly crossing a transiti onal 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 driftbottleneck 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 r estricted to Location 1, a na rrow cross-section back thr ough time. We might find re mains of species A, B, C, a nd maybe D, but not any ot hers until we reach G.
Macro Changes at Micro Levels Flight came later in birds. Immediate ancestors t o birds were ground- or tree-dwelling, reptilelike animals. Preadaptation, meaning that a structure or beha vior possesses the necessary form and function before being remodeled into a new role it later s
erves. 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 cel
ls called a somite grows downward along the sides of th e embryo at sites where fore- and hindlimbs are to form. Here, the somites lower growing tip meets special cellsmesenchymal cells, they initiate a limb bud. In legless lizards, lower tip of the somite fails to grow downward into the ar ea of the prospective limb. In the environment the limbless young realized some co mpetitive 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 wi ngs. In snakes, the Hox genes that regulate foreli mb development have deactivated normal for
elimb development, leading the absence of fo relimbs. Evolutionary significance Such large-scale change single gene mutation A hundred gene mutations the relatively few
First, group selection includes no plausible culling mech anism, no selective agent that sees or acts directly up on group traits. Second, most supposed cases of group selection obser ved in nature, in fact, when closely studied, collapse do wn to a special case of individual selection- kin selection .
G. G. Simpson was one of the first to recognize that the se saltational events between groups represented not a n artifact of preservation. Individuals in small, isolated populations experience extr eme conditions. Preadaptation is the evolutionary process wher ein ancestral structures come to serve in new w
ays Master control genes- Hox genes- control banks of genes that in turn manage the assembly of a n organism.
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