see Cultural traits transmission of
see Cultural traits transmission of
Catastrophes of global extent, which accompanied or were followed by mass extinction of species, could have been caused in history by the impacts of cosmic bodies, asteroids or comets. The impact of a sufficiently large body leads to mechanical and thermal destruction of an extensive territory and, in many cases, to the massive transport of dust particles into the atmosphere, causing prolonged changes in the light and temperature regime all over the planet. For example, the impact of a large meteorite causes destructive pressure waves, enormous tsunami, forest fires and subsequent acid rain or darkness as a result of dust and soot that destroy extensive ecosystems far away from the actual site of impact. It is not clear whether these phenomena lead to global warming or global cooling; it probably depends on whether cooling occurs as a consequence of shading of the surface of the Earth or warming as a result of the greenhouse effect. Study of impact craters on the Earth and Moon has confirmed that impacts of sufficiently large bodies on the surface of the Earth occur sufficiently frequently for this phenomenon alone to explain most of the mass extinctions distinguished in the paleontological record. It can be estimated that, approximately once every 400 thousand years, a body falls to the surface of the Earth and forms a crater at the site of impact with a diameter of 20 km and, once every 50 million years, a body falls forming a crater with a diameter of 100 km. If the frequency of formation of the individual size categories of craters is compared with the intervals between mass extinctions of a certain intensity (Fig. XXII.4), it follows that the impact of a body forming a crater with a diameter of 24 km should cause the extinction of approximately 5 % of species once every million years and the impact of a body forming a crater with a diameter of 60 km should cause the extinction of approximately 50 % of species once every 88 million years (Raup 1992). These figures follow from a certain unrealistic overestimation of the assumption that all the mass extinctions are the result of the impact of cosmic bodies. Nonetheless, it seems quite realistic, either from the aspect of the frequency of impacts of cosmic bodies and also from the viewpoint of their probable effect on biodiversity (Jetsu & Pelt 2000; Sepkoski 1989).
At the present time, most impact craters are under the surface of the sea and the craters that are located on the continents have been destroyed to a major degree by erosion. Nonetheless, a number of craters have been discovered whose age corresponds very well with the dating of a mass extinction. The Manson crater in Iowa is an example. This crater has a diameter of 32 km and is 65 million years old, the same age as the mass extinction that occurred at the end of the Mesozoic and beginning of the Tertiary. The Chicxulub crater, which is of the same age, has a diameter of approximately 300 km and is buried in the Yucatan Peninsula on the coast of Mexico (Sharpton & Marin 1997; Schuraytz et al. 1996). Possibly more than 50% of species became extinct at the end of the Mesozoic and beginning of the Tertiary, and this extinction apparently affected all types of ecosystems over the whole surface of the Earth (Raup 1994). Almost all of the big five extinctions and a great many less extensive mass extinctions are now related to an impact crater of the corresponding age.
In addition to impact craters, there are also further indications of the connection between mass extinction and the impact of a cosmic body. The most convincing of them is the occurrence of the iridium anomaly, i.e. the occurrence of layers with iridium concentrations that are elevated by more than an order of magnitude; this element occurs in only trace amounts on the Earth, while it is far more frequent in some cosmic bodies. The best known iridium anomaly was described in 1980 by the Nobel-prize winner L. W. Alvarez and his coworkers at the boundary between the Mesozoic and Tertiary (the KT-boundary) (Alvarez et al. 1980) It is interesting that this team was originally looking for evidence for the hypothesis that mass extinctions do not, in actual fact, exist and that the discontinuities in the compositions of the fauna and flora between some layers are a result of the fact that sediments were not deposited for a long time at the particular site. Only a minimum of iridium remained in the surface rocks of the Earth after cooling of the planet so that practically all of this element found in sediments is derived from meteorites or comets. Alvarez assumed that, even at times when no classical sediments were deposited, iridium was nonetheless constantly deposited so that the iridium concentration would have to be elevated in the layers of sediments that were deposited abnormally slowly. However, the measured increase in the iridium content at the boundary between the Mesozoic and Tertiary was 2-3 orders of magnitude and was thus so great that it could not be explained by gradual constant accumulation of this element. The period for which classical sediments were lacking would have to have been too long. The only reasonable explanation of the iridium anomaly seems to be a sudden, short-term increase in the amount of iridium that fell over the entire surface of the Earth during its collision with a cosmic body, most probably the core of a comet, approximately 65 million years ago.
Over time, it was found that the iridium anomaly and other geological indications for the impact of a cosmic body (chock minerals, microtektites) also accompany some other periods of mass extinction, for example the anomaly in the Frasnian period in the Devonian, the Callovian in the Jurassic, the Cenomanian in the Cretaceous and two anomalies in the Tertiary (Rampino & Haggerty 1996; Rampino, Haggerty, & Pagano 1997). Some of these indications can be found in layers of the same age even at very distant locations, while other similar anomalies tend to have a local character.
Formation of conditioned reflexes and other types of learning provide animals with good behavioral plasticity. They enable each individual of the given species to adapt to the particular local conditions, which can differ from the long-term conditions under which the majority of this kind lives. The individual can even adjust its behavior to stimuli it never experienced before. If an adaptation to a unique lifetime situation is to be created (e.g. the need to recognize its parents), learning may occur in the form of imprinting. If the individual encounters the appropriate stimulus at a given moment, e.g. when a freshly hatched young goose meets a colored ball or Professor Konrad Lorenz, it will imprint the particular object into its memory as its mother and for the rest of its life this stimulus will remain a trigger for particular behavioral patterns. Behavioral patterns created by imprinting are long-term or permanent and do not need strengthening to last. On the other hand, once they are created they are usually irreversible; they can not be changed when the external conditions change. In contrast, standard learned patterns can disappear more or less rapidly. To last, they need to be strengthened continuously by a repeatedly occurring combination of the stimuli that produced the patterns. In a changeable environment, this is advantageous because reflexes that are no longer useful for the organism can give way to new ones. Conversely, imprinting is useful for stimuli that will probably not change during the individual’s life, e.g. recognizing its mother or members of its own species.
Behavior-controlling mechanisms have appeared during evolution to enable organisms to react adaptively to the widening spectrum of stimuli coming from their surroundings. An inborn fixed pattern of behavior is the simplest mechanism. Some inborn fixed patters of behavior activate autonomously during the individual’s ontogeny -and life cycle, independent of the environment. They are activated without any external stimulus and their form and starting point are programmed genetically. In many cases, the neural system is not required for their coordination. This kind of behavior often occurs in plants, where it is accompanied or mediated by growth; it most probably also controls the embryogenesis of most organisms.
Inborn reflexive behavioris a type of behavior that is one step more complex. The unconditioned reflex is a prototype of this kind of behavior, but it is necessary to bear in mind that a simple reflex can be followed by a long sequence of other elements of behavior, of which some are fixed and some learned (see below). The organism’s reaction to a specific external starting stimulus consists in the activation of another specific pattern of behavior (e.g. the familiar patellar reflex). The specificity of the external starting stimulus ensures that the given patterns of behavior will be initiated in situations that are advantageous for the organism. This type of control lacks plasticity; it develops entirely in the process of natural selection which does not enable the organism to react to the momentary situation. From a statistical point of view and in the long-time perspective, the existence of a fixed pattern of behavior can be advantageous, but in some situations, especially under changing conditions, such a behavioral pattern can be fatal. Moths would certainly tell us something very ugly, if they could, about their current experience: For millions of years, they have oriented themselves according to light sources when flying in the dark; i.e. according to the position of moon and stars, objects infinitely far away from the practical point of view. If they were to do this in the present-day populated landscape, they would most likely end their lives by spiraling into hot light bulbs.
see superinfection and virulence
Inclusive fitness is one of two components of fitness, direct fitness and inclusive fitness.. Direct fitness takes into consideration reproductive success only of the particular individual, while inclusive fitness considers the reproductive success of both the particular individual and of his relatives.
For example, if the population contains an individual who helps his siblings, these individuals have, on an average, greater fitness than the other members of the particular population, even if they leave behind the same number of descendants. Their nephews and nieces have, in any case, at least ¼ of their genes in common because of their relatedness (the fraction of common genes can often be greater as a consequence of relatedness, as the relatives of particular individuals could have reproduced together in previous generations). From the standpoint of evolution it thus makes no difference if an individual assists in reproducing himself or two of his direct relatives or siblings (with whom he has at least ½ of their genes in common because of their relatedness) or 4 descendants of his descendant or sibling. Altruistic behaviour of individuals is thus worthwhile if
where r is the relationship of mutually assisting individuals, basically indicating how much larger will be the probability that an allele of the gene for altruistic behaviour will be shared by two specific individuals than that it will be shared by two randomly selected individuals in the population, b – the advantage that altruistic behaviour provides to the assisted individual and c – the cost that the assisting individual must pay for assisting. The price and the advantage are measured in terms of the relevant biological currency, i.e. in the biological fitness. Thus, under certain conditions, an organism can increase its fitness either by producing a greater number of descendants or by assisting its relatives.
see Spontaneous mutations
An interesting property of sexual selection lies in its marked inertia. At first glance, it might seem that, under conditions where feather length attains dimensions that are disadvantageous for their bearers, sexual selection should “shift to another track”. Females should appear in the population that would begin to select a sexual partner according to other criteria. However, imagine the situation encountered by a female that would begin to prefer males with shorter feathers. Her sons would inherit shorter feathers from their father and will thus have a greater chance of living to reproductive age than their competitors. It might seem that the offspring of the mutated female would have greater fitness. However, this is not true in actual fact. Most of the females in the population will continue to prefer cocks with longer feathers, so that the sons of the mutated female will have reduced sexual attractivness and therefore reduced fitness.
It can be demonstrated that the predominant taste of the females in the flock has a major effect on the reproductive success of males with various phenotypes, especially in polygynic species. In some species of fauna there is even a special ethological mechanism that further strengthens the inertia of sexual selection. It has frequently been observed in birds, mammals and fish (Dugatkin 1996; Agrawal 2001b) that females employ a male’s success with the other females in the flock as one of the most important criteria for selection of a sexual partner (Fig. XV.3). A female who saw that a certain male copulated with a great many other females also frequently prefers this male. This mechanism ensures that the females “need not” rely on their individual taste, but can base their selection of a sexual partner on the predominant taste of females in the particular population. This mechanism is especially advantageous when a female becomes part of a new flock. In order for her sons to exhibit sufficient sex-appeal in the new environment, it is advantageous if the female is able to subject her selection of a sexual partner to the momentary taste of most of the females in the flock.
This model can, of course, not be generalized; in some situations, to the contrary, the effect of the rare male is important. It has been observed in a great many species that above-average success in intrasexual competition is exhibited by males with rare, frequently striking phenotypes (Singh & Sisodia 2000). As was probably first noticed by Daniel Frynta of the Prague Faculty of Science (who, after his custom, did not publish it), the two contradictory effects are, in actual fact, not mutually exclusive and can be active simultaneously in a single population. While most of the females in a particular population systematically prefer males with the most common phenotype, these males tend to compete with one another. When a male with unusual phenotype appears in the population, he has a chance that he will have great reproductive success amongst some females whose individual taste he satisfies. Although most females will prefer the male with the common phenotype, males with unusual phenotype could exhibit the greatest “sexual fitness”.
– see Virulence
Frequently, only a small number of infectious stages of the parasite, and sometimes only one individual, enter the host organism. This individual can reproduce here and must form the infectious stage. A subpopulation of the parasite bound to a single host organism, called an infrapopulation, survives there for a certain time; this period of time is limited at one end by the moment of infection and, at the other end, by the moment when the host manages, for example through immune mechanisms, to destroy the parasite or when the host organism dies a natural death or as a result of pathogenic manifestations of parasitosis. From the standpoint of the growth rate of the overall parasite population, and thus from the standpoint of the evolution of the relevant parasite species, two parameters are most important – the number of infected individuals and the number of propagules, i.e. infectious stages that the individual parasite infrapopulation produces. In general, we can state that, under certain conditions, the rate of production of infectious stages by the particular subpopulation per time unit is more important while, under different conditions, the number of infectious stages produced over the entire time of existence of the parasite subpopulation, i.e. for the duration of infection of a single host, is more important. This is thus a system that, in a certain sense, is analogous to the model of turbidostatic and chemostatic selection. Parasite subpopulations bound to individual hosts can be exposed either to selection for greater rate of reproduction, for example, when there is a danger of frequent superinfection (i.e. the infection of an already infected individual), or selection for better (more economical) use of resources, in this case infected hosts. In the latter case, the critical parameter is not the actual growth rate of the infrapopulation, but the effectiveness of use of the infected host individual. Because the growth rate is not of fundamental importance, it can be quite low in some parasites and, in some cases, even zero. The parasite does not reproduce in the infected individual, only survives in a constant number of individuals and produces infectious stages.
A low or zero growth rate of the parasite infrapopulation is, in addition, also advantageous from the standpoint of protection against identification by the immune system of the host. Some components of this system react, not to the presence or absence of a foreign antigen, but rather to its potential dangerousness and thus, for example, to damage to the tissues of the host organism or to the very dynamics of increase in the amount of antigen in the organism. If a parasite reproduces exponentially in an organism, it becomes an easy target for the sensory components of the immune system and thus a probable object of attack by its effector components. If, on the other hand, the concentration of antigens does not change in the organism, or if it increases only slowly, the immune system does not act against the particular instigation. This “sneaking through” of an antigenic agent plays a negative role, not only in defense against a slowly reproducing parasite, but also in antitumour immunity, specifically in immunity failure against slowly growing tumours.
Reproduction or, to the contrary, absence of reproduction of a parasite infrapopulation in an organism currently forms a basis for separation of parasitic organisms into macroparasites and microparasites. While this division is correlated to a certain degree with parasite size or, to be more exact, with the ratio of the size of the bodies of the parasite and the host, the decisive criterion is, however, whether the size of the infrapopulation and thus most pathological manifestations of the infection are proportional to the number of parasite individuals infecting the particular host. Such a direct dependence exists for macroparasites, including, for example, tapeworms, nematodes and ticks; however, such a dependence is more or less lacking for microparasites, including, for example, Plasmodium, Toxoplasma, bacteria and viruses. Thus, from an ecological standpoint, some microscopic parasites belong amongst macroparasites, e.g. the cilita protozoan Ichthyophthirius, and, on the other hand, some macroscopic parasites would tend to be classified amongst microparasites, e.g. the larvae of flukes in snails, barnacles of the genus Sacculina (Kuris & Lafferty 2000).
see Cultural evolution
see Point mutations and also Mutations at the level of the entire DNA section
see Memes origin of new
see Selection kin
In unicellular organisms, cells are only rarely differentiated morphologically into microgametes and macrogametes. This is apparently a result of the fact that the unicellular organism and the unicellular gamete are exposed to very similar selection pressures in their environment, which does not permit them to differ much from the common structural plan in their morphologies. However, the situation is somewhat different for permanently attached (sessile) unicellular organisms. A different selection pressure acts on the gametes than on the sessile individual, as they must, at the very least, be capable of looking for one another. In this case, it can be expected that differentiation into microgametes and macrogametes will occur.
Differentiation into microgametes and macrogametes is more or less a general rule in unicellular organisms forming colonies and in true multicellular organisms. The phase of a multicellular, frequently macroscopic organism regularly alternates in the life cycle of the species with a mostly unicellular gamete phase. It is evident that the selection pressures acting on a macroscopic organism and a microscopic gamete are different. Simultaneously, especially microgametes are frequently produced in an enormous excess compared to macrogametes, so that the intensity of their mutual competition to find and fertilize macrogametes can be extremely high.
The aspect of intergamete selection warrants closer attention. At first glance, it may seem that its effectiveness must be incomparably greater than the effectiveness of selection at the level of an adult multicellular individual. One sperm from amongst millions participates in fertilization of an egg. However, it should be borne in mind that each gene occurs in the set of sperm derived from a single individual in only two variants, where 50 % of the sperm carry one variant and 50 % the other one. Thus, if the concepts of the theory of interallele competition are considered (see IV.9.1), it is apparent that, from the viewpoint of the individual alleles, this does not involve selection of one in a million but one of two. It is, of course, necessary to point out that new mutations formed during gametogenesis will be selected with an effectiveness of one in a million if they occur in the sperm population with this frequency.
Gametes and their multicellular organism have a common gene pool for their evolution. However, because they are exposed to different selection pressures, situations must necessarily occur in which a certain gene is exposed to two opposing pressures. From the standpoint of the chance of a multicellular organism surviving to reproductive age, it could, for example, be advantageous if the Michaelis constant for a certain substrate is a reduced for a certain enzyme while, from the viewpoint of the chance of microgametes rapidly finding macrogametes, it could be, to the contrary, advantageous if this constant is increased. As the intensity of the selection pressure on the gamete can be greater than the intensity of the selection pressure on its multicellular organism, it could easily happen that the interests of the gamete would predominate over the interests of the organism and evolution would proceed towards an increase in the Michaelis constant and thus in an undesirable direction from the viewpoint of the multicellular organism.
While the gamete can hardly affect the selection pressures to which the multicellular organism is exposed, the multicellular organism can very easily and very substantially alter the environment in which the gametes will live and thus the selection pressures to which they will be exposed. Some facts indicate that this targeted influencing of the gametes actually occurs.
The most effective mechanism capable of limiting inter-gamete competition and thus also the subsequent autonomous evolution of gametes consists in inactivation of genes in the mature gametes. For example, it is known that most of the genes in the sperm of vertebrates are completely inactive and that neither transcription nor subsequent translation occurs on them (Ward 1994). Highly condensed nuclear material, i.e. an indirect indication of gene inactivity, is found in the microgametes of most animals, plants and protozoa. Thus, most of the properties of sperm are not determined by the set of genes borne by the particular sperm, but by the set of genes of the multicellular organism controlling the processes of spermatogenesis and spermiogenesis in the sex organs. However, recent results have indicated that, in spite of the condensation of chromatin, expression of a great many genes occurs in microgametes. In plants, possibly up to 20 thousand genes are expressed in pollen grains and it has even been observed in vertebrates that some of the expressed genes affect such an important trait from the viewpoint of intergamete selection as flagella mobility (Olsson & Madsen 2001).
It is also known for a great many animals that the female does not leave the sperm to their fate in her reproductive organs following copulation (Pizzari & Birkhead 2000; Tschudirein & Benz 1990). Cases have been described in many species of animals, including human beings where the sperm in the reproductive organs are passively drawn in or rapidly moved by peristaltic motion to the sites where fertilization is to occur (Baker & Bellis 1993b). It cannot be excluded that the female thus prevents intergamete competition, here a race amongst the sperm for the fastest pathway to the egg.
An obvious requirement in defining taxa within a certain phylogenetic line is that taxa at the same level must not overlap and that certain species cannot be assigned to two various taxa at the same level. The only exception consists in species or phylogenetic lines that were formed, not by splitting of lines, but rather by fusion of species belonging to two different taxa. In this case, the relevant species and its descendants can be included in both the taxa from which the relevant parent species were derived and thus the taxon in which it finally ends up is only a matter of convention. Of course, it is more practical and more common to separate the descendants of such a fusion into a new taxon.
The entire system of overlapping taxa defined in the given phylogenetic line on the basis of the achieved level of anagenesis must also be created so as to reflect a certain hypothesis on classification of traits as homologies and homoplasies. In this respect, the system should be internally consistent. It is inadmissible to define a taxon so that its existence simultaneously necessarily requires the assumption that another taxon within the studied line is defined on the basis of homoplasy and is thus polyphyletic (Fig. XXV.7). Once again, it is necessary to bear in mind that all the taxa are, in actual fact, only our abstractions defined on the basis of subjective decisions. As individual taxa differ in their phenotypes, not in one, but mostly in a number of traits and, simultaneously, anageneses of the individual traits very frequently occurs independently and at various speeds, it need not necessarily be possible to create an internally consistent system of taxa based on the distribution of specific traits for existing species in a particular phylogenetic line. However, even this does not reduce the general requirements that the created system be unequivocal and not contain polyphyletic taxa. Our hypothesis about the classification of traits as homoplasies and homologies, on which the particular system is based, must, however, not contain any a priori inner contradictions.
Cladists generally hold the opinion that there is no difference between a polyphyletic and paraphyletic taxon that would be apparent directly from the topology of the cladogenesis scheme. This opinion has a certain realistic basis, as it holds that a paraphyletic taxon is a taxon defined on the basis of shared plesiomorphy, while a polyphyletic taxon is a taxon defined on the basis of shared homoplasy, where cladogenesis schemes do not, by definition, contain the relevant information related to anagenesis (otherwise they would be phylograms). In fact, however, it is possible to recognize the presence of polyphyletic taxa defined within a certain system even without knowledge of anagenesis and the distribution of the individual forms of the traits. In the absence of information on the distribution of the individual forms of the traits in modern species and their evolutionary ancestors, it is not possible to determine, on the basis of knowledge of cladogenesis, which of the defined taxa is paraphyletic and which polyphyletic; however, it is possible to determine that at least some of the defined taxa are polyphyletic and thus that the system as a whole is created incorrectly from the viewpoint of evolutionary systematics (see Fig. XXV.7c).
Reduced virulence amongst long-term adapted parasites is sometimes explained as a result of the action of interpopulation, interspecific or species selection. Some authors assume that populations or species of parasites that rapidly liquidate their host population are at a disadvantage compared to populations or species that spread more slowly and thus leave their host population time to regenerate. Consequently, parasites with greater infectiousness are at a disadvantage in interpopulation or interspecies competition.
This mechanism could actually participate to a certain degree in reducing virulence; on the other hand, as has been mentioned repeatedly, the effectiveness of interpopulation and interspecific selection is generally rather low. If the altruistic behaviour of parasites (for example a reduced rate of multiplication) is maintained only by interpopulation selection, then selfish individuals with greater virulence than that exhibited by the other members of the population can very readily emerge and predominate in the population.
Species selection has a somewhat greater chance of affecting the situation. This could be true in the given case because species of parasites with high virulence endanger the existence of their host population and thus simultaneously increase the probability of their own extinction. In nature, there is a greater chance of encountering parasites exhibiting lower virulence towards their natural hosts, as species with high virulence have probably long been extinct.
The driving force for evolution need not always be only selection following from intraspecies competition for the greatest resistance to pressures from the external environment and the best utilization of the resources that this external environment provides. In evolution, selection following from intraspecies competition can even lead to the formation of adaptations, structures and patterns of behavior that permit the organism to obtain advantages at the expense of the other members of the particular biological species and population and, simultaneously, of course, adaptations that allow individuals to prevent similar efforts on the part of the other members of the population. Thus, a constant evolutionary battle occurs amongst the members of a single species, in which individuals utilize various strategies which are intended to allow them to gain a certain advantage at the expense of the rest.
Some of the aspects of this evolutionary game can best be illustrated on the example of intraspecies competition in animals that most frequently have a rather familiar and therefore easily understandable form of competition of various patterns of behavior. However, similar evolutionary games also take place between plants and viruses; however, there they take the form of competition in the creation of various morphological or biochemical structures rather than various patterns of behavior.
In the following text, we will be concerned with the progress of such evolutionary games only on examples of competition of various patterns of behavior in animals. However, such an approach has certain drawbacks. If people compete together (for example play chess, football or shoot ballistic rockets at one another), they consciously choose a strategy, mostly from a number of strategic alternatives. Simultaneously, they usually know the goal that they want to achieve and also know the probable effects of the chosen strategy on their competitors and teammates. It cannot be excluded that a similar view into the rules and progress of the battle is also valid to a certain degree amongst some animals (see XVII.3.1). However, it is rather improbable and, especially, uninteresting from an evolutionary standpoint. In evolution, traits, here patterns of behavior, are of importance if they are determined genetically and are thus heritable. Thus, if we state that a female must try to force a male to invest the greatest possible amount of energy into building a nest in the precopulation phase of reproduction, then we are using our anthropomorphic terminology. If we wanted to avoid this at any cost, we would have to say: “Only those females will remain permanently in the population that carry a gene or genes that directly or frequently indirectly affect their behavior in a manner such that they will reproduced with those males that have, in their genome, a gene or genes that directly or frequently indirectly affect their behavior in a manner such that, in the precopulation phase, they will invest great efforts in the construction of a nest.”
If we compare the length and comprehensibility of the two sentences, the comparison will most certainly favor the anthropomorphic terminology. However, the use of this terminology is simultaneously somewhat misleading; in the absence of appropriate emphasis to the contrary, it could create the impression in the reader that the strategy is chosen by individuals in the same way as in people, i.e. on the basis of free choice. It must again be emphasized that, whatever the terminology or strategy being discussed in evolutionary biology, the individual organisms do not choose voluntarily or consciously, that they simply behave as dictated directly or indirectly by their genes. Most individuals do not use a certain strategy because it will probably be successful. Rather, because this certain strategy has already been successful, the population contains a predominance of individuals that use it.
Here, it should be recalled that it makes no sense to attempt to evaluate the evolutionary strategy of organisms from ethical viewpoints or, to the contrary, look for justification for some form of human behavior in the evolutionary laws of intraspecies competition. The laws of ethics do not make any sense amongst animals; in human society, they should, to the contrary, be preferred over biological laws in all cases.
In gonochorists, the individuals within the species have been differentiated into males and females. The two sexes differ in a number of traits and each has its specific role in the biology of the species. As a consequence of this division of roles, the strategies that the members of one or the other sex can use to gain an advantage at the expense of the other members of the particular species also differ. We can best understand the concept that the members of one sex can attempt to gain an advantage at the expense of members of the other sex. And this is actually frequently the case. However, it should always be recalled that a similar and usually much more intense battle for gaining advantages at the expense of another individual also occurs constantly amongst the members of the same sex.
The course and evolutionary consequences of intersexual and intrasexual competition, similar to the course and consequences of the competition of any alternative game strategies can be estimated using the mathematical discipline, game theory (see IV.5.1 and XVI.5). For example, game theory can be used to determine the optimum strategy for males and females and the results of intersexual competition. We can also determine what is evolutionarily stable strategy (ESS) in the given case (see IV.5.1). The optimum strategy and evolutionarily stable strategy need not be identical. In more complicated games, where there is a predefined role of the competitors and teammates, the optimum game strategy can be considered to be the strategy that brings the teammates the greatest advantage at the expense of the competitors, for example the maximum average reproduction success of males at the expense of females. In contrast, evolutionarily stable strategy is strategy that, when it predominates in the population, permits gaining the maximum advantage at the expense of teammates, here members of the same sex, following any other (minority) game strategy.
The following text will be concerned primarily with competition between members of different sexes, intersexual competition. The best known manifestations of competition between members of the same sex, intrasexual competition for sex partners, i.e. sexual selection, will be discussed in a separate chapter (XV).
Affecting the sex of offspring is one of the areas in which a conflict of interests can occur between the interests of males and females. The most extreme cases occur once again amongst hymenopterous insects, where the males do not have the least interest in their sons with whom they do not share any part of their genome (daughters obtain half their genes from their father and half from their mother, sons have all their genes from their mother). In the mentioned parasitic wasps of the Nasonia genus, the male cannot affect the decision of the female in any way; in another hymenopterous insect Tripoxylon politum, it seems that it at least tries to (Dawkins 1976). In this case, the female lays the eggs immediately following copulation. The male holds the female by the head for about 30 seconds after copulation and apparently attempts to prevent her from laying any eggs. It cannot be excluded that, through this forced prolonging of the interval between copulation and laying of the eggs, it could perhaps increase the chance that the eggs will be fertilized prior to laying.
The conflict of interests between the male and female is not as strong in diploid organisms, but still occurs to some degree. This could follow, for example, from the fact that the female must invest substantially more in the production of offspring than the male. Consequently, for example, situations can occur where it would be more advantageous for the father to kill embryos or zygotes of a certain sex, while this would not be worthwhile for the female.
see Selection intraspecific and interspecific
The theory of aging based on interspecific competition seems to be the least probable at the present time (Nusbaum 1996). According to this theory, it is advantageous for a species if its members age and die and make room for new individuals of the particular species. In this way, the population can gradually evolve to adapt to changing living conditions. A basic drawback of this theory is that it does not take into account the simultaneous opposite action of individual selection. It could be advantageous for a species as a whole if faster and better adaptation of the gene pool of the population to external conditions is facilitated through programmed death of individuals. However, it is advantageous for the individual member of the population if he ages as slowly as possible and lives as long as possible and consequently leaves the greatest number of progeny. Any mutation that causes slowing of ageing in its carrier will increase his individual fitness and will thus have a tendency to increase its frequency in the population and finally become fixed, without regard as to whether its fixation reduces the chance of long-term survival of the entire species.
see Selection intraspecific and interspecific
see Intra-individual competition
Intra-individual competition and the consequent intra-individual cell line selection are mostly, but not necessarily always (see XII.220.127.116.11) undesirable from the standpoint of maintenance of the integrity of a multicellular organism. If the cells could compete together, those that were capable of the fastest reproduction and the most effective spreading in the body of the organism would, in time, predominate in the individual. Then these cells would multiply at the expense of those that invest their energy into performing their physiological functions in the body of the multicellular organism rather than into their own reproduction. Those cells that would be capable of preferentially occupying the position and function of precursors of germinal cells would then predominate at the population level. The most important consequence of the existence of a single-cell phase in the life cycle of organisms is that all the cells in the body of a multicellular organism are mutually genealogically related and thus genetically more similar than the cells occurring in the bodies of two multicellular individuals. Genetic similarity and, if we ignore newly formed somatic mutations, even genetic identity of cells in an organism fundamentally limit the occurrence of mutual competition of cells and cell lines within the multicellular organism – intra-individual competition of cell lines.
see Selection intraspecific and interspecific
see Impacts theory of mass extinctions
A number of “missing” intermediate links exhibiting the traits of two distinct extant taxa have already been found. However, an even greater number never existed at all and thus there is no point in being surprised by their absence in the paleontological record (Fig. XXVII.2). In a great many cases, the common ancestor of the two taxa lacked all the traits that are characteristic for modern members of these taxa, so that the link between the taxa cannot be recognized on the basis of its phenotype. The relevant characteristic traits developed in each taxon only gradually over an extremely long period of time.
The situation encountered in the search for links between the individual related species, e.g. within a single genus, is somewhat different and far more interesting. The absence of transition phenotype forms between the parent and daughter species is very remarkable in a great many species of organisms. This fact is reflected in the paleontological record in that a certain species has the same phenotype throughout its existence and then, suddenly and apparently with no transitory forms, a species with a different phenotype emerges next to it and then accompanies the original species in the paleontological record, or replaces it. The new species then also does not change throughout its existence. This situation is described by the theory of punctuated equilibriums (see XXVI.5.1). The punctuated character of the evolution of species is frequently contrasted with the apparently generally anticipated character following from Darwin’s theory of evolution.
To begin with, it is necessary to explain what the paleontologist means by suddenly replace. This generally occurs in a time period of the order of tens of thousands of years which, from the viewpoint of the duration of the existence of a species (several million years) is a short period of time, but is sufficiently long for the formation of a new species by Darwinian mechanisms. It should further be pointed out what is the usual population mechanism of the formation of a new species according to current evolutionary concepts. This involves the mechanism of allopatric speciation, i.e. speciation that occurs in a geographic area away from contact with the original species. In fact, this very frequently involves peripatric speciation, i.e. the formation of a new species in a small, separate population. A great many such populations are formed during the existence of a species; however, they mostly last only a short time and, after some time, disappear or merge with the original population. The probability that gradual phenotype changes will occur in one of these small split-off populations is, for a great many reasons, substantially greater than the probability that it will occur in the large parent population (XXI.3.1). Simultaneously, there is negligible chance of encountering such a population in the paleontological record. Thus, the sudden appearance of a new species in the paleontological record is thus actually a result of the invasion of an already existing species into a new territory and not of its instantaneous emergence at the particular location. The relative lack of paleontological records for the slow development of one species from another species is thus a quite logical consequence of the character of long-known evolutionary processes and certainly does not constitute an argument against the validity of the modern the theory of evolution.
This popular objection is again untrue. To begin with, it is necessary to clarify what we mean by the formation of a new species. A great many breeds of dogs have been bred over a time period of the order of hundreds of years. In their phenotype, they differ to such a degree that, if a paleontologist were to discover their skeletons, he would not hesitate a moment to assign them to different species or even genera. Nonetheless, we do not consider them to be separate species because they can interbreed. The formation of a new species amongst sexually reproducing organisms is considered to occur when a reproduction barrier is formed that prevents interbreeding between the members of the old and new species. We have repeatedly been witness to the formation of such a barrier in nature and in the laboratory. For example, it is sufficient for two lines of drosophila to be infected by different strains of bacteria of the Wolbchia genus so that they are no longer capable of interbreeding because of the “cytoplasmatic incompatibility” of their members (see XXI.5.4). Similarly, for example, if cholchicine is used to derive a tetraploid plant from a diploid plant and the former is propagated vegetatively, both the tetraploid and diploid plants will be capable to interbreed; however, frequently it will not be possible for the diploid plants to interbreed with the tetraploid plants. Simultaneously, tetraploid plants frequently have very different phenotype than diploid plants and also differ in their ecological requirements – thus they comply with both criteria for a separate species – i.e. they have a new phenotype and are reproductively isolated. If we really wanted to create a new species of dog, it would actually be possible. It would be sufficient to imitate extinction speciation (XXI.2) and kill off all breeds of dogs except St. Bernard’s and Chihuahuas...
According to the opinion promulgated by some opponents of the theory of evolution, scientific facts should be taught at schools and not unverified theories.
To begin with, it should be pointed out that this opinion is not generally held. A non-negligible part of the public thinks that, rather than teaching actual facts, schools should teach students how to discover these facts and how to deal with them. Acquainting pupils and students with unverified theories is very useful for acquiring and developing these skills and may even be essential. In actual fact, this book refers to some more “exotic” theories and hypotheses for just this reason.
Secondarily, this objection is proof of the person’s lack of knowledge or failure to understand the basic principles of general scientific methodology. Every theory or hypothesis actually represents a model of a certain phenomenon (process) and thus our idea of why and how a certain phenomenon occurs. The only way to verify whether our model is the correct one is to verify the truth of all the consequences following from the potential validity of our model. Consequences following from the model can have the nature of a statement with a general quantifier (It holds for all X that Y, for example, “All organisms on the Earth use a universal genetic code”) or a statement with an existential quantifier (There exists at least one X for which it holds that Y, for example “An animal exists that is capable of obtaining all the necessary organic carbon by photosynthesis."). Empirically, i.e., for example experimentally, it is possible to confirm the validity of statements with an existential quantifier by actually finding some X for which it holds that Y. However, these statements cannot be empirically proven to be untrue as we can never be sure that we have examined all possible X. In contrast, statements with a general quantifier can only be shown to be untrue empirically in that we find at least one X for which Y is not true; however, the validity of a statement with a general quantifier can never be confirmed, because once again we can never be sure that we have examined all X. However, the meta-statement mentioned at the beginning of this section, “All the consequences following from the potential validity of our model are true.” has the nature of a statement with a general quantifier and thus, in the optimum case, we can overturn it but never prove it.
The philosopher Karl Raimund Popper (1902–1994) was apparently the first to quite convincingly demonstrate that it is not possible to prove, i.e. verify, any scientific theory. It is only possible to attempt to overturn it, i.e. falsify it. If a theory is capable of resisting sufficiently intense attempts to overturn it for a sufficient length of time, it can be considered to be relatively verified and thus conditionally valid. However, no theory can be considered to be definitively confirmed; it is always necessary to bear in mind the possibility that even the best-confirmed theory may be erroneous. The requirement that only scientific facts be taught and never unverified theories is thus not practicable unless, of course, we don’t want to limit ourselves to teaching some parts of mathematics.
At the present time, there are apparently no scientists concerned with the origin and development of life who would doubt the very existence of biological evolution and its importance for the origin and development of organisms. The individual mechanisms active in biological evolution and also their relative importance for the origin and development of organisms are understandably a subject of professional discussion and scientific research. In this area, the theory of evolution has, of course, undergone very significant development since Darwin’s time (see XXVIII) and it can certainly be anticipated that this development will continue.
As shown by sir K. Popper, it is not possible to prove any scientific theory. Thus, the difference between a scientific and unscientific theory cannot be its provability. However, the difference lies in the fact that, for an unscientific theory, there is not even a theoretical possibility of overturning it. If someone is of the opinion that all species of creatures were created by an omnipotent God, he might well be right; nonetheless, his theory of the formation of life will not be scientific as it is not possible to in any way disprove it. If God is truly omnipotent, then He could foist any arbitrary results on us in our experiments and observations. In contrast, an enormous number of specific consequences follow from the theory of evolution and these can be gradually tested empirically. If these consequences were to be shown not to be valid, we would have to reject the theory of evolution. For example, if paleontologists were to demonstrably find a Paleozoic fossil of a mammal or if molecular biologists were to discover that there is usually no agreement amongst the phylogenetic trees created on the basis of various genes, i.e. that each gene would have its own unique evolutionary history, we would have to reject the theory of evolution in its present form. Thus the theory of evolution cannot be proven, in more or less the same way that any other scientific theory cannot be proven. However, it can very easily be shown to be false, and thus it rightly belongs amongst fully sound scientific theories.
Statistical reasons for the impossibility of the formation of an organism would be valid only for a single-step emergence. However, the theory of natural selection assumes the gradual, multi-step formation of living systems. The differences can best be illustrated using the well-known thought experiment (Fig. XXVII.1). If we sit a troop of apes down to typewriters and teach them to press the keys, there is only a negligible probability that any of them would write a sensible sentence within a reasonable period of time by only randomly pressing the keys, for example a sentence such as “Taken statistically, it is impossible that something as complicated as an organism could be formed by a random process of evolution.”. If, however, we have each ape press only one key, then send him back to the trees, we can find which of them wrote the letter “T”, copy this onto papers which we put in all the typewriters and request the apes to hit another key, etc. this sentence will be written with surprising speed. Darwin’s the theory of evolution assumes that random processes play an important role in the development of life, but not a decisive role. In the process of mutagenesis, random processes only generate the individual changes, from which the process of natural selection then non-randomly chooses those variants that improve the functioning of the whole system.
The second law of thermodynamic is valid only for the organization of isolated systems. In open systems, i.e. systems that exchange energy and mass with their surroundings, the degree of organization can both decrease and increase (Prigogine & Stengersová 2001). Energy from the Sun constantly impacts on the Earth and, on the other hand, thermal energy is constantly irradiated back into the surroundings. This means that the overall degree of organization of the Sun-Earth system decreases, while the degree of organization of the Earth increases at the expense of the rest of the solar system. Similarly, the individual living organisms have an increasing level of organization at the expense of the organization of the substances that they consume.
This is once again an argument that has arisen in various forms since the time of Darwin. Originally, anti-evolutionists liked to put forth these arguments in connection with the structure and function of the eyes of vertebrates. The eye has a great many components, where any of them would see to be essential for the creation of an image. However, the eye is a very unsuitable example for this type of argument. It is quite true that all the present-day components are necessary for perfect vision. However, it is simultaneously obvious that even the simple ability to differentiate light and dark is very useful for the survival of an organism; it is somewhat better to recognize the direction from which the light is coming and even better to roughly differentiate the shape of objects in the field of vision, etc. Thus, a perfect eye can be very easily formed by the gradual evolution of its components, where every evolutionary step put its bearer at an advantage compared with its less perfect predecessor.
The opponents of the theory of evolution tend at the present time to concentrate on the purported irreducible complexity of molecular structures, such as the molecular apparatus employed for rotating a bacterial flagellum (Behe 2001a; Behe 2001b). These structures are usually less complicated than macroscopic structures, still their functionality , such as the ability to rotate a flagellum, is dependent on the existence and functioning of all the components. Anti-evolutionists argue that these components could not have evolved gradually in the process of evolution, as one of them makes no sense in the organism without the other.
A fundamental error in this argument is that it ignores the existence of exaptations, i.e. structures that developed in evolution in a different functional context than that in which they function in modern organisms (see I.7.1). The individual components of the flagellum apparatus most probably developed independently of one another, under the effect of various selection pressures and originally performed a completely different functions. At some point, the finished components were ordered in a functional apparatus, that began to be capable of performing, originally probably rather imperfectly, a new function, here rotating a flagellum and thus allowing the bacteria to move. The molecular apparatus of a bacterial flagellum has a great many components in common with the molecular apparatus employed by a great many bacteria for injecting toxin into the cells of an attacked organism, and also with the F1-ATPase molecular apparatus, i.e. the molecular complex synthesizing ATP at the expense of the transmembrane proton gradient (Block 1997; Noji et al. 1997).