Theory of Evolution by Natural Selection

Australia has unique fauna

Australia has unique flora

Biological Diversity

Biological diversity refers to the variety of all forms of life on Earth, the diversity of the characteristics that living organisms have and the variety of ecosystems of which they are components. Diversity within a population is what allows it to adapt to changes in the environment.

Biodiversity exists on three different levels:

Genetic diversity, which refers to the total number of genetic characteristics in the genetic make-up of a species
Species diversity, which is a measure of the diversity of different species in an ecological community
Ecosystem diversity, which is the variation of different ecosystems found in a region.

Genetic diversity

Genetic diversity within a species is important for populations to adapt to changes in the environment. Environments are constantly changing and in this way pose selection pressures that enable some organisms with favourable characteristics to survive and reproduce more successfully than others.

Populations with limited genetic diversity risk extinction in the long term. If there is genetic diversity in the population there is a chance that some individuals will have a pre-existing ability to survive and go on to reproduce.

For example, calicivirus is a virus that affects rabbits. It kills 95% of rabbits within the first 72 hours. This virus has been used as a biological control mechanism in Australia. However, 5% of rabbits are immune to the disease. These individuals will go on to reproduce and pass on the immunity to their offspring.

Mule that has taken on more donkey traits

Mule that has taken on more horse traits

Mule with a fairly even mix of traits

Darwin-Wallace theory of evolution

Evolution is a change in living organisms over a long period. The theory has cropped up a few times in history but was never fully accepted. All theories of evolution share some common basic premises:

Living organisms arose from common ancestors or a common life form and have changed over time.
Differences that occur among groups of living organisms imply that living things change over time.
Similarities occur in living things and suggest a common ancestry - the basic chemistry, inherited from a common life form, has remained relatively unchanged and has been passed down through generations.

The Darwin-Wallace Theory of Evolution by Natural Selection is based on the premise that living things arose from a common ancestor and that some populations moved into new habitats where they adapted over time to their environments, leading to the diversity of life.

Natural selection depends on the following concepts:

Variability: all populations have random differences or variation among their members
Heritability: variation may be inherited
Over-reproduction: organisms produce more offspring than the environment can support
Competition between organisms and survival of the fittest.

This theory gave rise to the idea of Speciation. Darwin and Wallace proposed that the formation of a new species may occur when a population becomes isolated from the original group of organisms. Only the individuals who's variation allows them to survive the change will reproduce, which will eventually mean the population becomes so different that the original population is not able to interbreed with them to produce fertile offspring.

For example, mules are the result of a male donkey and a female horse. Their features will vary significantly. Horses have 64 chromosomes while donkey's have 62. This means the mule has 63 chromosomes which means that the different structure and number of chromosomes means that most mules are infertile (although some are able to).

Characteristics of horses, donkeys, and mules

Charles Darwin

Neo Darwinism

Scientists more recently have applied concepts of Mendelian genetics to support and explain Darwin and Wallace's ideas on random genetic variation leading to gradualism and the formation of new species.

In any population, although offspring resemble their parents, they are not identical to them. The term variation applies to differences in the characteristics of individuals within a population. When organisms reproduce, the offspring resemble their parents in basic structures.

Many variations arise from the interaction of an organism with its environment. This type of variation affects the individual organism. Variations that can be passed on from one generation to the other - heritable characteristics - affect evolution. Heredity and variation are essential for evolution to occur. Variations that pass from one generation to another are often produced in a population as a result of mutations.

It is important to remember the individual does not develop an adaptation in response to the environmental change. Organisms must already possess the random variation that confers an advantage under the new conditions. This variation is then called an adaptation. An adaptation provides an advantage if a selection pressure is introduced in the environment, thus allowing them to out-compete organisms without the adaptation.

Allopatric speciation involves genetic change due to geographic isolation

Allopatric speciation

Closely related species whose distribution overlaps are called sympatric species. Species that are geographically isolated are called allopatric species. Allopatric speciation is speciation that occurs when populations become isolate. This involves:

In a parent population that has a large range with a common gene pool, there is regular flow of genetic material within the population.
Part of the population becomes separated by a physical barrier. This prevents the flow of genes of the isolated individuals.
The two populations experience different selection pressures that favour some individuals over others. This alters the frequency of specific genes. The isolated population will eventually become a subspecies.
If the populations are separate long enough, the gene pool will change drastically so that interbreeding is no longer possible.

Allopatric speciation versus Sympatric speciation

Biodiversity over time with note of extinction events

The origin of life on Earth

The fossil record does not necessarily show a uniform pattern of change that supports slow change. Fossil evidence shoes that after a major extinction event, new life forms flourish. For example, it seems that after the extinction of the dinosaurs, mammals were able to take advantage of the new ecological niches left open due to the reduced population.

Biodiversity and major extinction events

It is believed that the environment on early Earth provided conditions for inorganic molecules to form organic molecules. Organic molecules then reacted with each other to form more complex organic compounds. Complex organic compounds then became separated from their surroundings when membranes formed around them. This is how we think the first prokaryotic cells were formed. The separation of these cells from their environment would have allowed the entities to metabolise more effectively.

Further advances happened as cells specialised over time. Evidence suggests that this came about by endosymbiosis, the ingestion of smaller cells into larger cells, creating organelles such as chloroplasts and mitochondria. These would have been the first eukaryotic cells. with cells now able to photosynthesis they were able to diversify and become more complex, eventually becoming larger and multicellular.

Endosymbiosis

The move from unicellular to multicellular began with the clustering of eukaryotic cells. when some cooperation occurred, colonial organisms resulted, giving them an advantage over unicellular organisms. Once cells started to specialise to carry out specific functions, higher organisation was possible, resulting in multicellular organisms.

Fossilised Cycad

Life has increased in complexity and diversity

Diversification of life on Earth

As multicellular organisms developed, life began to diversify further. Invertebrates developed 600mya, fish in 425mya and amphibians 345mya. A large extinction even then occurred and amphibians began to decline. This was followed by the rise of reptiles marking the beginning of the Mesozoic era 250mya. This era included the Jurassic and Cretaceous periods when dinosaurs roamed.

With the extinction of the land reptiles, mammal-like reptiles took hold 230mya. The extinction of marine and aerial reptiles followed. While the reason for these extinctions is still debated, enormous change in the environment was the root cause. The organisms with the diversity to adapt were able to survive the extinction events.

Plants were also undergoing diversity changes with cycads, conifers and gingkoes being dominant in the Jurassic period and flowering angiosperms evolving 135mya.

The Cenozoic era saw the rise of mammals. During the quaternary period megafauna mammals became extinct. This occurred just as humans began expanding their range. There is still debate about the main cause of the extinctions with human interaction being theorised to have had an impact.

Some organisms appear to change very little over time. The Coelacanth, Cycads, Tuatara, and Horseshoe crabs are examples. Rather than suggesting that they have not changed, it is their environments that have not changed meaning they have not experienced a significant selection pressure.

Coelacanth

Horseshoe crab

Major diversifications in the history of life

The Geological time scale and the diversity of life

Palaeontology is the study of fossils, which provide us with evidence for the diversity of living things on Earth over time.

The geological timescale was a model that was developed to show the changes to diversity. Initially miners noticed that specific rock strata contained fossils. Nicolaus Steno stated in 1669 that sedimentary rocks were laid down in layers, with the oldest being on the bottom. James Hutton added in 1795 that geological processes were uniform in frequency and magnitude (uniformitarianism.

It is evident that natural selection may result in changes within a species (microevolution) or it may result in populations that a wildly different from their ancestor, creating new species (macroevolution). For speciation to occur there must be population isolation.

The theory of evolution by natural selection was proposed by Darwin before there was any knowledge of genes or an explanation of how inheritance works.

Events that caused diversification

The theory of evolution suggests that all living organisms come from a common ancestor, which evolved into many different organisms over billions of years. Natural selection provides a mechanism by which this can happen. The table summarises major events in the appearance of life on Earth and its diversification.

Evolution from abiotic to biotic:

The basic molecules of life on Earth are water and carbon. Carbon is an ideal molecule for the basis of life, as it is a stable framework for development of complex molecules, and is readily available in the environment. The four macromolecules which form life, protein, nucleic acids, carbohydrates, and lipids, all utilise carbon as a basis. Current theories suggest that within the right conditions, in the presence of the right conditions, in the presence of the right substances, abiotic molecules, such as water and carbon, were able to evolve to become biotic, in a process called abiogenesis. Primordial cell structures formed as a result of abiogenesis.

Prokaryotic life:

Some of the earliest pieces of evidence for the start of life on Earth include fossilised microorganisms found near hydrothermal vents at the bottom of the ocean. It is also theorised that ancient microbial mats, stromatolites, were the site of early life-form evolution, due to their chemically diverse environments and range of microorganisms. Although the evidence for when and how exactly life on Earth began is inconclusive, it is clear that its origins are found in prokaryotic, unicellular organisms, composed of very basic structures, appearing in the fossil record about 3.5 billion years ago. It is thought that these prehistoric microbes were responsible for oxygenating the atmosphere, allowing for the evolution of complex eukaryotic organisms.

Endosymbiosis:

It is currently widely accepted that eukaryotic organisms began to evolve as a result of endosymbiosis. This is a process in which it is theorised that small prokaryotes either invaded or were engulfed by larger prokaryotes, and continued to live and evolve inside these organisms. These are thought to be the basis of mitochondria and chloroplast organelles within cells. these endosymbionts were beneficial to host cells, as they provided more machinery for producing energy and food sources, potentially enabling cells to become more complex as these were more readily available.

Eukaryotic life:

Algae and fungi are currently thought to be the earliest forms of eukaryotic organisms, as evidenced by the fossil record appearing around 1.5 billion years ago.

Sexual reproduction:

Prokaryotic organisms reproduce by binary fission, where daughter cells are identical to parent cells, whereas eukaryotic cells reproduce by meiosis and fertilisation. This allows for increased genetic variability, as there are new combinations of genes are more chances for mutation events. It is unclear when or why sexual reproduction arose in the evolution of life, but a many animals, plants, and fungi reproduced this way.

Multicellular organisms:

Evolution of multicellular organisms was advantageous, as it allowed more efficiency in sharing nutrients, increased resistance to predators, and the ability to create a more stable internal environment. Multicellular eukaryotes are thought to have begun large-scale diversification around 1 billion years ago.

Animals:

The earliest animal lifeform are theorised to be the cnidarians (jellyfish) which are distinct from other multicellular eukaryotes due to a lack of cell wall, and their motility. They emerged around 580 million years ago, followed by a proliferation of eukaryotic lifeforms.

Vertebrates:

About 500 million years ago during the Cambrian explosion animals began to become more structured, developing different mechanism of rigidity. Some animals developed rigid outer 'shells'. Others developed a rigid spine-like rod, and some jaws, the beginnings of modern vertebrates. These were the beginnings of the evolution of fish within the ocean.

Evolution onto land:

Of those 'shelled' organisms which evolved in the ocean, so ventured onto land, and evolved flaps on their backs, eventually becoming modern insect wings. Fish also began to develop backbones, and increased skeletal structure within their fins. Following this, some began to evolve onto land, breathe air, and their fins evolved into leg structures. These were amphibians, which still required water for reproduction, but could survive on land. From amphibians, reptiles began to evolve, removing themselves from water environments by evolving scaly skin and the ability to lay eggs.

Dinosaurs:

Dinosaurs were a group of reptiles which dominated with Earth during the latter part of the middle Triassic period. Although a large-scale extinction event wiped out most of these land vertebrates, birds had evolved from Theropod dinosaurs. Prehistoric mammals and monotremes also evolved from reptiles, and proliferated after the extinction of dinosaurs.

Modern descendants:

Modern animals and lifeforms are the descendants of these prehistoric creatures, and have evolved and adapted as the Earth's environment has changed over millions of years. Humans have evolved from a species of upright-walking appears over 6 million years, Homo erectus first appearing somewhere between 1.8 and 0.2 million years ago.

Variation always occurs within a population, no matter how fundamental or simple the organism. This means that over billions of years, simple cells were able to become complex organisms as their populations expanded, they naturally mutated, and the Earth's environment continued to change and place selection pressures on them. The simple mechanism of natural selection therefore accounts for the huge variation that we see today.

Evolution onto land

Dinosaurs

Evolution from abiotic to biotic

Prokaryotic life

Endosymbiosis

Eukaryotic life

Sexual reproduction

Multicellular organisms

Animals

Vertebrates

Modern descendents

Macroevolution vs Microevolution

Micro-evolution and Macro-evolution

Evidence suggests that change in the environment is a driving force behind change in living organisms. The environment can be defined as the biotic and abiotic surroundings of organisms.

Sheep breeds are examples of microevolution whilst the different animal phyla are examples of macroevolutions

Micro-evolution vs Macro-evolution

Microevolution: Occurs on a small scale, within a species; for example, an increase in the frequency of a certain trait within a population.

Macroevolution: Happens on a scale that goes beyond the boundaries of individual species, such as the origin of a new species from an ancestor.

Speciation: Is the formation of a new species as a result of evolution.

As a result of environmental change, resources may become limited and so living organisms will begin to compete for the available resources in order to survive. Competition will arise between organisms for resources such as light, soil nutrients and water in plants, or food, water, shelter, mates and territory in animals. Change in the environment of a population influences evolution because it results in selection pressure acting on organisms.

Selection pressures include:

Environmental change
Competition
Predation
Disease

It is commonly accepted that physical and chemical changes in the environment may have caused past extinction events and evolution of modern organisms. Evolution may be considered over very long periods and over shorter periods.

Macroevolution takes place over millions of years, measured as geological time, and results in new species arising
Microevolution takes place over shorter periods and results in changes within populations but does not produce new species. New forms that arise within populations can be referred to as varieties, races or breeds.

Microevolutions can lead to speciation. For example small changes over time led the dog-sized ancestor of the horse to evolve into the large modern day animal. The slow progressive accumulation of changes can have dramatic effects.

Evolution of the horse over time

Evolution of the Horse

The evolution of the horse species is a great example of the process because of the extensive fossil record that exists showing its changes. There exists a series of fossils which show physical changes within a single lineage.

The modern horse is a product of millions of years of evolution, beginning with the ancient Hyracoherium, a small forest animal only 10-20 inches high, which resembled more a dog than a horse. Its notable features included 4 toes on each front foot and 3 toes on each back foot, each ending not in claws but hoof-like appendages, and omnivorous teeth. This genus gradually evolved become Epihippus, quite similar to its ancestor, but with more grinding teeth, as the diet of the species changed to predominantly plant material.

As the climate of North America began to change, becoming drier and dominated by grasslands, the ancestral horse developed even tougher grinding teeth to consume grasses, and became larger with longer legs, suitable for speed in open areas. This was a sudden speciation, due the selective forces of a changing environment, with the emergence of the Miohippus genus.

During the Miocene period (18 million years ago), horses evolved to better consume grasses. They developed "Hypsodont" teeth; teeth which grew continuously out of the gum as they were worn down by chewing grass. The jaws also developed ridges for more efficient grinding. Species in this period were also better adapted for running, with increased leg length, body size, and elongation of the face. The Merychippus genus was 40 inches tall, with a more horse-like face. Although it still has 3 toes, it was spring-footed, meaning it walked on tip toes rather than on pads like it's dog-like ancestors.

From the Merychippus genus a species of one-toed horses evolved, as a result of slow reduction in the size of their 'side-toes' and strengthening of the ligaments around the central toe. Around 4 million years ago the genus of all modern horses, Equus, appears in the fossil record. They were around the size of a pony at this stage, with long legs, long necks, long faces, a typical horse-like body, and deep jaw. This genus spread across the globe during the late Pliocene period, diversifying into the modern Zebra in Africa, and spreading to Asia, Europe and South America.

Modern theories explain horse evolution in terms of microevolutionary changes in genes which led to speciation over time. Microevolution explains why so many different variations of horses existed. Genetic variation caused by mutations, natural selection, genetic drift and speciation are all processes that could have contributed.

The Platypus is a unique animal with traits of several different organisms

Evolution of the Platypus

Australia has unique animals such as Marsupials (pouched mammals), monotremes (egg-laying mammals) and a few placental mammals (internally developing mammals). Marsupials give birth to live young that are at a very early stage of development and so the young live in the pouch were they grow and develop. Monotremes include the echidna and platypus, animals whose young develop and are nourished as eggs.

The platypus is a monotreme native to the eastern rivers of Australia. Placental mammals, of which there are only a few in Australia, nourish their young inside the body via a placenta. The fossil record of the platypus is very poor. Monotremes were present in the Mesozoic era, when Australia was part of Gondwana. The evidence suggests that they originated in the Australia/Antarctic section of Gondwana.

The platypus has features that are similar to birds (bill and webbed feet), reptiles (venom glands, egg-laying with a leathery shell), and mammals (hair and milk-producing). Original samples were thought to be fake and it was officially named Platypus anatinus in 1799 by Dr George Shaw. The name means flat-footed duck-like. This name was later changed to Ornithorhyncus anatinus after a double up was discovered (the name was already given to a beetle), with the new name meaning bird-like snout, duck-like.

An ancient group of reptiles called cynodonts are believed to be the earliest ancestor of mammals. Genetic evidence suggests that monotremes split off first (150mya) and have been evolving ever since. This split was followed by marsupials (130mya) and the placental line of mammals branching off (110mya).evidence suggests that therian mammals gave rise to marsupials and placentals around 148mya. Recent DNA analysis of modern echidnas and platypus, as well as fossil evidence, suggest that the platypus and echidna have a common ancestor. Technology such as molecular dating has been used to identify that the platypus and echidna split from a common ancestor about 19-48mya.

The Cynodont is believed to be the earliest ancestor of mammals

Biologists use branching diagrams called cladograms to depict the evolutionary relatedness of organisms. Each point where the lines branch indicates a split from a common ancestor. Studies of fossil evidence and the genome of the platypus have led scientists to discover that the platypus is not directly related to birds. It is a descendant of a reptile lineage from millions of years ago. This lineage gave rise to marsupials, birds, reptiles, and placental mammals. The platypus split from the placental line about 166mya.

A cladogram demonstrating how the main classifications of animals evolved from a common ancestor

Comparing the genomes of the platypus, marsupial and placental mammals shows that about 82 per cent of genes are common to both. The platypus lays eggs with a yolk, whereas humans do not produce eggs with yolk. Scientists have discovered a gene in the platypus, absent from humans, for the production of a yolk protein. However, all three groups have two genes related to tooth production which, together with the presence of a third gene for the production of a milk protein, seem to be necessary for lactation.

The existence of venom is typical of reptiles such as snakes. The platypus is also able to produce venom in a claw on its hind legs. However, this does not mean the two species have a common ancestor. This is an example of convergent evolution.

Recent discoveries of platypus-like fossils have led to a whole new area of research among platypus species. In the past the platypus was thought to be a left-over unevolved organism, but it is in fact a highly evolved form of an ancestor. There is fossil evidence of only three types of carnivorous mammals - the marsupial lion, the thylacine and one carnivorous kangaroo - which is lower than South America which has up to 60 different carnivorous predators.

Fossil evidence shows that the modern platypus is more specialised than its ancestors; for example, they no longer have teeth, but instead have horny pads. They also have a highly evolved sensory system associated with their bill - an electroreception system for detecting prey in murky water. In addition, the current platypus is distributed in a more limited area than was seen in the past, now restricted to river systems on the east coast of Australia.

Evolution of the platypus is considered typical of macroevolution, having taken place over a very long period and resulting in the evolution of new species.

Evolution may cause increased or decreased similarity in organisms

Convergent and Divergent evolution

In closely related species, the basic similarities between organisms could be as a result of their relatively recent divergence from a common ancestor - divergent evolution. More distantly related species which have moved into similar environments and been exposed to similar selective pressures evolve to become similar - convergent evolution.

Darwin and Wallace

Both Darwin and Wallace studied large numbers of living organisms and observed that similarities in structure were common. These similarities can be accounted for in one of two ways:

In closely related species the similarities could be a result of their relatively recent divergence from a common ancestor. Natural selection accounts for their differences whereby being exposed to different selection pressure could result in them becoming more and more different. This is Divergent evolution.
If more distantly related species show similarities this could be due to similar environments. That is the two organisms were exposed to similar selection pressures and so natural selection causes them to be more and more similar. This is convergent evolution.

The Darwin-Wallace theory of evolution by natural selection and isolation accounts for both types of evolution as the organism changes due to a change in environmental pressures.

Adaptive radiation is a term used to describe the evolutionary variation in species that evolved from a common ancestor. Because of the migration of organisms into new environments, organisms begin to occupy new niches.

Placental animals and marsupials that have evolved to be fairly similar based on their environments

Species increase in similarity

Convergent evolution

Convergent evolution: Is the process by which organisms which are not closely related evolve to have similar traits, because they have adapted to a similar environment.

Darwin and Wallace's theory of evolution by natural selection explains cases of convergent evolution, as natural selection provides a mechanism which selects for traits best suited to a particular environment.

Sharks and dolphins are not closely related, as sharks are fish and dolphins are mammals. However, they both live in water, and have some very similar traits, including fins, tails, and the fact they are strong swimmers. Both populations of ancestral sharks and dolphins would have naturally been varied, some of them with stronger swimming tails and others without. When the selection pressure of an oceanic environment was applied to those populations, those with stronger swimming tails (similar to modern sharks and dolphins) will have survived. Those surviving individuals will have reproduced, passing these traits onto their offspring. This process will have continued as sharks and dolphins continued to live in the same environment, under the same selection pressures. In this way, their evolutionary pathways converged.

Sharks and Dolphins have similar streamlined bodies to suit their aquatic environment

Flying animals feature wings with similar features

Species diversify

Divergent evolution

Divergent evolution: Is the process by which organisms which have recent common ancestors (i.e. are closely related) evolved to have different traits, because they have adapted to different environments.

Divergent evolution is almost like the opposite of convergent evolution. The theory of evolution by natural selection likewise explains how it can occur in populations.

Looking at the example of Darwin's finches on the Galapagos Islands, we can see that they all have very different characteristics. Some had long beaks, capable of piercing fruit to eat the pulp. Others had short, strong beaks, able to crack nuts. Others could only eat insects, or leaves, all due to the shape of their beaks.

This variation is because each type of finch is located on a different, separate island. Each island carries with it its own selection pressures, which in this case is food sources. Although the finches are all closely related, when they were separated on islands with different food availabilities, they had to adapt to survive. On an island abundant with nuts, those in the initial population with a beak best suited to cracking nuts would have survived, as they could eat the abundant food source. They would have passed this trait onto their offspring, and eventually the trait of a short strong beak would have become the major characteristic in the population. They will have changed in some way from their ancestors, due to being isolated on different islands, and each species will have diverged in their evolutionary pathways.

Darwin's finches diversified in beak shape to suit their food sources

Slow changes vs rapid changes

Gradualism and Punctuated Equilibrium

Punctuated equilibrium and gradualism are two types of evolution that can occur in a species. A species can exhibit one or both of these evolutionary patterns. Some scientists are speculating that the type of evolution is determined by time. Species that have evolved over a longer time exhibit gradualism. Both models are valid in explaining macroevolution.

Evolution of Trilobites

Gradualism

Gradualism as proposed by Darwin suggests that populations slowly diverge by accumulating changes in characteristics due to different selection pressures. This pattern of evolutionary change suggests that transitional forms should exist. Trilobites are a group of marine invertebrates that show evidence of gradualism in their fossil record.

Fossil evidence that indicates each model

Model of gradualism vs punctuated equilbrium

Punctuated equilibrium

Punctuated equilibrium is an evolutionary theory proposed by Eldridge and Gould in 1972. this theory suggest that’s there are short periods of rapid evolutionary change, during which new species will emerge, followed by long periods of stability, stasis during which a population will remain largely unchanged. Periods of rapid change are triggered by a change in environment, creating new selection pressures, and such change will more likely occur in smaller, peripheral populations. For example, the occurrence of an ice age or a sudden period of heat on Earth will have triggered changes to many species.

This contrasts the previously accepted norm in evolutionary biology, Darwinian ideas of gradualism, in which change to a species occurs slowly and uniformly over a long period of time.

"The absence of fossil evidence for intermediary stages between major transitions in organism design, indeed our inability, even in our imagination, to construct functional intermediates in many cases, has been a persistent and nagging problem for gradualistic accounts of evolution." - Gould

The theory of punctuated equilibrium is consistent with the fossil record, where there are rarely instances of continually changing species.

Comparison of gradualism and punctuated equilibrium

Theory of Evolution by Natural Selection

Inquiry question: What is the relationship between evolution and biodiversity?

Explain biological diversity in terms of the Theory of Evolution by Natural Selection by examining the changes in and diversification of life since it first appeared on the Earth
Analyse how an accumulation of microevolutionary changes can drive evolutionary changes and speciation over time, for example:
- Evolution of the horse
- Evolution of the platypus
Explain, using examples, how Darwin and Wallace's Theory of Evolution by Natural Selection accounts for:
- Convergent evolution
- Divergent evolution

Explain how punctuated equilibrium is different from the gradual process of natural selection

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