For an explanation, see the main splats page
SPLATS about the nature of evolution
- The nature of evolution
- Evolution is mainly about changes in gene frequency, caused by natural selection of those individuals better suited to the conditions in the recent past.
- The thing to keep in mind with evolution is that individuals do not evolve. The things which evolve are genes and gene combinations that are selected by chance.
- Extinction is the fate of all species, as a species, but in many cases, their descendants survive as new species. Some species will die out entirely.
- The key to understanding evolution is that all populations contain individuals which have varied forms, and these forms can influence the chances of survival.
- The variation within a species derives from mutations: these provide a basis for selection of traits which can be inherited, leading to new gene frequencies.
- Because of natural selection, most individuals are well-suited for where they live. A mutation changes this and usually makes individuals less well-suited.
- Many mutations that survive are minor changes that make little difference unless the environment changes, when they can suddenly become important.
- All organisms change over time as the conditions in which they live change. Today's cockroaches only look like ancient ones. They are genetically distinct.
- The term "survival of the fittest" is misleading. Evolutionary survival does not mean staying alive, but managing to produce viable offspring which are fertile.
- One standard view of evolution is gradualism. Another standard view of evolution is punctuated equilibrium. The truth probably is a mix of the two viewpoints.
- Evolution does not always lead to an improvement. In fact, most evolutionary paths lead to a dead end of specialization and extinction when conditions change.
- Under normal circumstances, when a species become extinct, it will be replaced by one or more other species or subspecies, usually from nearby.
- When a species or subspecies moves into a new niche, those individuals are often isolated from the parent population, and slowly diverge new directions.
- Evolution can be made easier by an isolating mechanism, which allows the founder effect to operate in the first place, and then makes genetic drift more likely.
- Evolution can be assisted by ecological isolation which lets new varieties avoid being swamped by weight of numbers or out-competed until they are established.
- Isolation can take the form of geographical separation where breeding individuals from the two populations simply do not ever having contact with each other.
- Isolation and can also take the form of behavioural separation where the two populations read at different times more in different ways, so genes don't mix.
- Every living thing shows adaptations that make it better able to live in the habitats where it is found than others, or it would not be able to flourish there.
- In the absence of selection pressure, small populations may differ from other populations in random ways as a result of the founder effect and genetic drift.
- Genetic drift happens in small populations as a result of the occasional chance loss of genes from the gene pool. Once lost, genes can only rarely be replaced.
- The founder effect can be seen in small isolated populations where only a few related individuals or families established the original breeding population.
- Without selection pressure, the Hardy-Weinberg Law says gene frequencies will not change in large populations, so any changes indicate some form of selection.
- As a general rule, things which look very similar have evolved from a common ancestor, although evolution can also make different lines look fairly similar.
- Some biochemical functions are so essential that they appear, almost unchanged, in all life forms, because any change in their operation would bring death.
- Key genes are conserved over very large time scales, because mutations in those genes tend to be lethal. This is why humans and yeast have some common genes.
- Homeotic genes perform the same function in very different organisms, directing the formation of parts like legs and eyes, and are yet to be fully understood.
- There is a sequence or progression of inter-relationship from predation to parasitism to commensalism, which can even become a limited form of symbiosis.
- Many organisms that start out in a predator-prey relationship evolve into a symbiotic relationship which benefits both organisms as this favours both parties.
- Many forms of behaviour are inherited, and so some sorts of behaviour are able to evolve, if they give some sort of advantage in reproduction or survival.
- Atmospheric pressure and density affect many animals, while gravity affects all land animals and most aquatic animals. This plays a role in evolution.
- The laws of physics affect animals in many ways, often influenced by the scale of the animal: think of an ant and an elephant falling off a cliff together.
- Evolution on another planet with different gravity might produce very different results, some of which would be hard to predict in advance of going there.
- Herbal drugs rely on chemical effects that have evolved over long periods, so they are likely to be at least biologically active against some forms of life.
- The laws of physics and the strengths of living materials place strict limitations on how large individuals can be in particular environments and habitats.
- If an animal doubles its length, its weight increases eight-fold while its legs are four times as thick, meaning there is a much greater loading on each leg.
- If a bird doubles its length, its weight increases eight-fold while its wings have four times the area, meaning there is a much greater loading on each wing.
- Evolution in animals favours shapes which experience less drag. This accounts for the similar streamlined fish-like shapes of marine reptiles and mammals.
- In 1862, Henry Walter Bates observed mimicry of distasteful or poisonous species by harmless, palatable species in butterflies now known as 'Batesian mimicry'.
- The number of closely competing types in an area seems to be controlled by guild theory, which sets the limit at about seven. Nobody really knows why.
- The Archaea are alive today, but they appear to be very similar to the oldest forms of life in terms of the way they live and are internally organized.
- There ought to be about 30 members of the Archaea that cause diseases in humans, but there seem to be no pathogens at all among this ancient group.
- Nobody is quite sure why that should be, but it is likely that by 2020, we will have worked out why the Archaeans don't cause disease, and why it is important.
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