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UNIT 3: EVOLUTIONARY THINKING AND EVOLUTIONARY
THEORIES
3.1. CREACIOTIONISM AND EVOLUTIONISM
3.1.1. Creationism In essence, the Creationism establishes that all the species were created at the same time and they have not changed since their creation. The world is conceived as something unchangeable and static.
3.1.2. Evolutionism before Darwin’s theory: typological thinking (essentialism) The typological thinking/Essentialism supports the idea that every natural system can be classified in natural categories, each of them defined by a permanent essence that differentiates it from the rest. While trying to announce a compatible theory between essentialism and evolutionism, two different evolutionary theories appeared:
- Transmutationism (or saltationism): evolutionary changes are the result of sudden and continuous changes from one species to another, but this theory does not explain what the cause of these jumps or mutations is.
- Transformationism: evolution is a gradual change lead by internal (essential human tendency) or external causes (environment), but this theory does not the differences between individuals of each species.
3.1.3. Darwinian Evolutionism: population thinking
Darwin said that the species evolve because every individual is different from the other. That is why some of them are better adapted for their survival and reproduction. This is the NATURAL SELECTION principle; the existence of differently adapted individuals in species is the mechanism that can lead the evolutionary change (the change in heritable traits of a population over time).
3.2. EVOLUTIONARY EVIDENCES 3.2.1. Fossil record The time between fossils and their age can be determined thanks to the modern techniques of geological (radioactive components of the rocks) and biological dating (DNA molecules), giving us valuable information about evolutionary process.
3.2.2. Homologous traits Homologous traits are those shared by different species that have a common ancestor (historical origin) and that have also been altered due to ecological pressure in order to adapt themselves to different environments. The most well-known example is that of the limbs:
3.2.3. Analogous traits Analogous traits are those which look similar but have different origins (both species don’t have a common ancestor), and there has been a convergent evolutionary process due to the fact they have all adapted to similar environments, so their similarities were not inherited.
3.2.4. Molecular similarities All living cells share some fundamental biochemical similarities:
- All cells have DNA as the carrier of genetic information,
- All cells use RNA, ribosomes, and approximately the same genetic code to translate that genetic information into proteins,
- All cells use roughly the same set of 20 amino acids to build proteins,
- All cells use ATP as a cellular energy carrier.
3.2.5. Vestigial traits and Atavistic traits Vestigial traits are those characteristics that are present in all the individuals from same specie without exception. Some examples are: the coccyx bone and some tiny muscles related with the horripilation (both in humans). Other examples:
Similarities between different species can be explained because of geographical facts throughout history (The theory of the Continental Drift-Alfred Wegener). That is why organisms exposed to environmental pressure in separate, but similar, geographical areas, tended to develop equal traits.
3.3. DARWINIAN THEORY
3.3.1. Facts and inferences of the Darwinian Theory See pages 115, 116 and 117 from the book Fundamentos de psicobiología I (Fernando Colmenares Gil).
3.3.2. Hypothesis of the Darwinian Theory of Evolution See pages 118 and 119.
3.4. POST-DARWINIAN THEORIES OF EVOLUTION
3.4.1. Evolutionary/Modern Synthesis Theory (1937-1950) It is said that this theory is a synthesis between Geneticists (random genetic variation: mutations) and Naturalists (non-random genetic variation: natural selection) ideas in order to explain the process of evolution. This theory establishes:
- Evolution can be defined in terms of (a) changes in the frequency of alleles (gene variants) in a population (anagenesis) and (b) changes in the number of species (cladogenesis), across generations.
- Evolution is gradual and results from the constant accumulation of small variations over long time spans.
- Natural selection is the main mechanism responsible for evolutionary change and for the suite of adaptations defining the organisms’ design.
- Microevolution (phyletic evolution) and macroevolution (speciation) are governed by similar mechanisms.
3.4.2. Punctuated-equilibrium Theory (1972) Basically, it says that evolutionary change is not gradual, it is episodic and it occurs during cladogenesis and not during anagenesis as the TS establishes. The main ideas are:
- Microevolution (phyletic evolution) and macroevolution (cladogenesis) happen respectively. There are long periods of evolutionary calm with short and strong periods of phenotypic changes that generate new branches in “life-tree”
- Phyletic evolution can be gradual, in fact, it is a process of relative absence of change, dubbed stasis.
- Many traits of organisms are not adaptations, but exaptations. Its existence is not the result of natural selection, but of other processes, such as genetic drift, allometry, developmental and phylogenetical constraints, etc.
3.5. EVOLUTIONISM AND HEALTH SCIENCES
3.5.1. Evolutionary principles useful for health sciences See table 3.4. (pages 127 and 128 in the book) 3.5.2. Coevolution and arms race The symbiosis is the interaction between two different organisms living in close physical association. The disbiosis is the biological condition, generally associated with a disease, in which there is a mismatch in the relation between an organism and a microbe. There are different types of symbiotic relations:
Mutualism/Commensalism (+/+): each part obtains a profit from the other part. Examples: bacteria, fungus, protozoan and vertebrates that accommodate them in their digestive system (endosymbiosis).
- Parasitism (+/-): when an organism takes advantage of another individual (the one who generally ends dying). The parasite: avoid, counter-attacks and destroy the host’s defenses and manipulates the host. Examples: mosquitoes, predator-prey model…
*Cleptoparasitism: it is a type of parasitism in which one individual steals a pray or other resources (an animal of a different specie) to another one from the same or different species.
The arms race between humans and microorganisms has led to the development of different weapons to fight one against each other. The main weapon of microorganisms is their high multiplication rate, while human’s weapon is our intelligence that has allowed us to create antibiotics (a faster way to eliminate microorganisms, in contrast with our immune system).
- Competition (-/-): both individuals are competitors because there are limited resources. The effect is mutual and negative for both of them. Examples: organisms that compete for a common resource (food, reproduction, light hours…)
