Genetic changes that lead to the creation of a new species are known as evolution. Life has evolved for over 3.5 billion years, and species rarely survive beyond a few tens of millions of years. About 300 million years ago, plants were able to colonize dry uplands. Whole groups of organisms have evolved and become extinct. Some in mass extinction events fossils reveal a pattern of rapid bursts of evolution.
Evolutionary innovations have allowed new niches and allowed newly evolving groups to diversify into them. Additionally, mate change changing sea levels, extensive volcanism, and plate movements have affected evolution in different places.
With the Origin of Species, Darwin transformed science and provided a mountain of evidence for the evolution of life by natural selection. But there were also holes in the evidence, which have since been filled in many times over. Let’s go over a quick summary of the main types of data that illustrate how evolution happens. The first of these types involve direct observation.
What is evolution?
Evolution is any change in alleles’ frequency in a gene pool, anything that causes specific alleles to become more frequent while other ones become less frequent. Evolution is a scientific theory that states that plants and animals change genetically over time, modifying and adapting over generations according to the demands of the earth’s changing environments. This biological process includes reproduction, diversification, and adaptation.
Charles Darwin formulated his theory of natural selection in 1839 called the process of descent with modification. The descent from a common ancestor with the improvement of biological characteristics. Over time natural selection is a key evolutionary process brought about by the survival of organisms best suited to their local environments, the survival of the fittest.
Evolution is fueled primarily by the processes of selection and competition. These act upon species that respond by having offspring that contain inherited variations. Most species tend to produce more offspring than survive natural selection favors and promotes the fittest’s survival. Those best adapted to the physical and biological environment, such as a particular climate or predator escaping. These survivors select other similarly adapted mates to produce offspring that survive in more significant numbers to breed new generations.
Without adaptability, life would never have moved out of the ocean. However, even adaptability is primarily a result of cause and effect. Life cannot predict a future need. Instead, new traits are produced in individuals by genetic variation and mutation.
The fossil record shows that throughout the earth’s history. Species have evolved and died out the majority of species that have developed and died out. The majority of species that have evolved are now extinct, but their genes survive in living descendants. Speciation is how new species evolve from an ancestral species, and it can be brought about in many ways.
Additionally, various regional and global environmental catastrophes have impacted life and resulted in mass extinctions. The largest of these at the end of the Permian times caused 96 of all species on earth to die out, yet life recovered.
What are the mechanisms of evolution?
We are going to talk about the remaining mechanisms of evolution, selective and non-selective ones. There are 5 mechanisms of evolution. Natural selection, sexual selection, artificial selection, genetic drift, mutations, and gene flow. Evolution is referred to as macro and microevolution.
Macroevolution: Macro meaning big, so when changing overtakes long scale time. Dinosaurs share a common ancestor that gave rise to a bunch of different species or types of dinosaurs. It takes a very long time to occur.
Microevolution: Micro meaning small, like a species of insects. Those small-scale changes in allele frequency in the population.
The selective mechanism has 3 types of selection.
- Artificial selection.
- Natural selection.
- Sexual selection.
Artificial selection is when humans choose which organisms reproduce and pass their genes on to progeny. Examples:- Cows, dogs, horses, innumerable fruits, and vegetables. Artificial selection requires only two of the three criteria. There is variation in the population, and the trait is heritable. The difference with artificial selection is that humans decide which traits are passed on, not nature.
Artificial Selection is used in agriculture and animal breeding all the time. People want cows that produce the best and most milk, so they don’t breed low milk production ones. Likewise, horses have various breeds for various jobs, and breeders use artificial selection to do this. All the different breeds of dogs are a result of this as well.
Darwin was also the first to evidentially articulate the idea that some organisms choose mates based on, in a sense, beauty. This is sexual selection. Peahens will, for instance, choose peafowls with brightly colored tail feathers. And this has been going on for long enough that modern peafowls have evolved extremely extravagant feathers.
Sexual selection has to do with an adaptation that makes an organism more likely to find a suitable mate. Continual sexual selection has given rise to sexual dimorphism, a difference in secondary sexual characteristics between a species’ males and females. It is certainly evident in humans. But it takes many other forms, like the brightly colored male peacock. And the variety of mating calls and dances performed by males of different species. These are examples of intersexual selection, choosing mates based on specific traits that indicate healthy genes, like bright colors.
Natural selection was first formally described by Darwin in his 1859 book On the Origin of Species. In which he concluded that nature selects which organisms passed traits on to their progeny. He reason that there was no hand guiding this descent process with modification but instead thought that organisms that were fit enough to survive did reproduce and passed on their traits.
Natural selection guides evolution, as this can pertain strictly to variance in a trait, like a neck length for giraffes. Genetic drift highlights how chance events, like the random elimination of homozygous organisms for a particular trait. It can cause the gene pool of a population to skew in a specific direction gradually. It is magnified when a few organisms become isolated from a larger population. Any deviation in this smaller group will be more statistically significant than otherwise expected. This is called the founder effect.
Similarly, a sudden change in the environment, like a fire, drought, or flood, can produce a bottleneck effect, dramatically reducing the population. By chance, specific alleles’ frequency may change suddenly due to the random nature of the survivors’ alleles. So genetic drift is significant in small populations. It can lead to a random change in certain alleles’ frequency, leading to a substantial loss in genetic variation within a population.
Nature is blind, and it works with the traits at hand. It can’t build new features from scratch. When land-bound creatures evolve into flying ones, they don’t just sprout wings. Their arms slowly become wings over many generations and many intermediate characteristics.
Flaws in the design of structures like the giraffe’s neck, with its laryngeal nerve’s completely illogical pathway. With its blind spot and other flaws, the human eye shows how nature built upon what was already there to get to something workable, though imperfect. There are so many factors simultaneously at play, but the result is a vast ecosystem of organisms well suited for their environments.
Natural selection can change a population in different ways depending on the change in the environment. It can describe by 3 selections.
- Directional selection.
- Disruptive selection.
- Stabilizing selection.
In directional selection, natural selection is taking place in a single direction. There’s a shift in one direction. As a result of natural selection. What happens if a beetle population moves into a new environment that has dark soil and dark vegetation? The dark beetles are going to blend in the medium-colored beetles.
And especially the light-colored beetles are now going to stand out. Suppose they stand out. That makes them more easily seen and eaten by predators. So the dark green beetles survive. They finish the sentence and pass on those dark green beetle jeans to the next generation.
Stabilizing selection is selection towards the middle trait and against the extremes. Imagine our original population has light green beetles, medium green beetles, and dark green beetles. What happens if that beetle population moved into a new environment covered in medium green colored ferns? It would not benefit from being dark green. It would not help to be light green. The medium green will blend in, making you more likely to survive, reproduce and pass on those medium green jeans.
It is the opposite of what you have selected against the middle and instead selection towards both extremes. Imagine our original population like green beetles, dark green beetles, medium green beetles. What happens if that beetle population moves into a new area that’s covered in both light green moss and dark green shrubs? The dark green beetle is going to blend in with the dark green shrubs.
The light green beetle blends in with the light green moss. They survive and reproduce. And the medium green beetles are now going to stand out. They don’t blend in with either of those things. So they’re going to be more likely to get eaten. It means they will decrease gradually.
A species is a member of the same organism that can reproduce and produce fertile offspring within its natural habitat. That is speciation, the formation of a new species through evolution. Scientists wanted to see this happen in a lab. A team of scientists took fruit flies. They took some fruit flies and split them into two groups.
In one tank, they fed them starch, and in the other tank, they fed them maltose. So all they changed was their food source! They let the fruit flies eat the food over a couple of weeks. They went through many different generations and just let them reproduce over several generations in a very short period.
What they saw was a change in color because of the food source. It makes sense that their color changed. But surely not enough genetic changes have occurred that they would be entirely new species. They put the two populations together now in a tank. And they let them do their fruit fly thing, and they all tried to mate with each other because that’s what fruit flies do. They found that only the fruit flies that had the same food source could reproduce new offspring.
Speciation has two theories that are explaining the rate of speciation. The interaction of a population with its environmental changes can lead to different rates of speciation. The two rates of speciation theories are called gradualism and punctuated equilibrium.
Gradualism – The gradualism model says that species diverge very slowly and that those changes occur in tiny steps until many generations later. This you typically see in huge populations where the environment is very stable.
Punctuated equilibrium – It says that species diverge very rapidly and that the change occurs in bursts, and then it’s followed by long periods of no change. This typically occurs in small populations where they have rapidly changing environments. So some environmental change causes a huge burst in a change in the population. And then it might be a long time where there’s no change.
Natural selection patterns
Evolution can follow several different patterns depending on the pressures that are being put on the environment. It is 3 types. They are:
- Divergent evolution.
- Convergent evolution.
- Coevolution evolution.
Divergent evolution: It explains homologous structures and why structures that are similar in different organisms. It suggests that they have a recent common ancestor and that they’ve diverged from one another.
Convergent evolution: Two unrelated species evolve traits and become similar because they live in similar environments. For example, fish results in the arctic and antarctic have evolved and freeze proteins in their blood for a long time. Scientists thought they must have evolved from the same ancestor.
But when scientists studied those antifreeze proteins, they realized that they were different from one another. It suggests that they evolved that trait utterly separate from one another because of the cold water. The environmental stressor was the same.
Co-evolution: The simultaneous evolution of two unrelated species because of their interaction and relationship with one another. For example, the bats and the flowers in the tropical regions. The flowers are light in color and smell fruity because the bats can see and smell. The flowers that had those traits survived and reproduced. The bats pollinated them. The bats evolved to have these long slender muzzles because that allowed them to get the nectar in these different flowers.
Natural selection causes enough changes to accumulate that an entirely new species will develop.
Non Selective Mechanism
In minimal populations of organisms, the founder effect and genetic drift can greatly magnify certain traits. For example, a small population of penguins moved to a place uninhabited by other penguins they could mate with. And those penguins were to reproduce and grow in population size, and then the founder effect might cause one or more genes to predominate in a population. It causes a loss of genetic diversity. Genetic drift is similar to aging and does not necessarily have any benefits that may predominate in a population due simply to the random sampling of genes.
For example, among Amish communities in Pennsylvania, Ellis’s crippled syndrome has become very prevalent because the colony members in 1744 had the syndrome. After years of interbreeding, the syndrome has spread throughout the population. It is important to remember that the mechanisms of evolution with selection in the name aren’t random.
Nature or humans are selecting organisms based on their traits. The process of natural selection is very non-random. The founder effect and genetic drift, on the other hand, are somewhat stochastic.
Genetic drift is the change in the gene pool of a small population.
There are two types of genetic drift.
- Bottleneck effect.
- Founder effect.
Bottleneck effect: It happens from a natural disaster by chance, and it reduces the population size. Earthquakes and volcanic eruptions are great examples. It changes the population size.
Founder effect: This one results from the colonization of a new location by a small number of individuals.
Non-random mating: The non-random in the population will change, increasing the frequency of specific alleles.
Mutation: Mutations happen just because the organism needs something to support its needs. Mutations are not always harmful or beneficial sometimes. It could be neutral, meaning they don’t do any harm or they don’t do any benefit. Mutations occur randomly and allow the organism to survive better. It also happens to the gametes over an organism. This forms in the egg because that’s the only mutation that can pass down to other organisms.
Evidence for evolution
Whenever we try to use drugs to kill pathogens, like certain bacteria, it is inevitable that a drug-resistant strain evolves and proliferates quickly, as it is immune to the drug. The resistance is not a product of evolution. It comes about by blind chance, but the proliferation of the resistance is a natural selection product. The lone resistant bacterium won’t be killed by the drug while the other bacteria will. Eventually, all the bacteria in that vicinity will be descendants of the initial mutant and thus also resistant to the drug.
Adaptation occurs with short-lived animals like bugs. When certain insects modify their food sources, their appendages change over many generations to better suit their surroundings. The strains of bacteria capable of metabolizing nylon, which humans invented in the 20th century. Thus, evolution by natural selection is not relegated to conjecture.
Another source of evidence for evolution is in the homology that exists between species. Homology is a word that refers to structural similarities in certain species as a result of common ancestry. Look at the arms and legs of humans and any other mammal, even whales, and bats. And see that they have remarkably similar bone arrangements, even though one is used to walking, swimming, and flying.
These homologous structures are entirely consistent with the idea of a common ancestry for all mammals. All vertebrates, including humans, have a small tail early in embryonic development. This is easily explained by considering that all vertebrates have a common ancestor.
When anatomical features are not useful to the organism, we call these vestigial structures, which we now understand are remnants of ancestors’ features. These evolutionary relics include pelvis and leg bones in snakes and the remnants of eyes in blind fish that live in pitch-black caves.
When phenotypes don’t match, there are still genotypes that link. Even humans and bacteria, showing how such incredibly dissimilar species must still have a distant common ancestor. This is why all life on a single evolutionary tree, the tree of life.
We get an idea of what kind of organisms existed and when which helps us fill in the gaps between existing species. The fossil record helps assign dates to the emergence of different species, including homo sapiens. Countless times, fossils have cropped up that provide missing links between various classes of organisms.
Archaeopteryx demonstrated a link between dinosaurs to birds. Other fossils found that act as intermediates between land mammals and ocean mammals like whales and dolphins. With each discovery, the tree of life grows more consistent with evolution by natural selection.
The study of how different species are distributed around the globe. The continents move slowly over millions of years, with specific areas connected in the past, which aren’t any longer.
Genetic variation makes evolution possible. Any novel trait that an organism can exhibit must result from a change in gene expression products, resulting from an alteration somewhere in the DNA sequence. Natural selection guides this process. Genetic drift and gene flow are other ways that genetic variation can propagate.
First, let’s recall that many phenotypic traits are determined based on two alleles: homozygous or heterozygous if mutations occur in the introns of a gene or the exons in such a way that the mutation is silent. It will not produce any change in the organism. By the point of mutations, a change in a single base pair can produce novel proteins. If this mutation occurs in cells that produce gametes, this change will be passed on to offspring. Typically, this will result in a less effective protein and will therefore be harmful to the organism.
If this is the case, the new allele will be removed by natural selection unless it is recessive, which may proliferate. There are so many genetic diseases that stem from recessive alleles. But some mutations result in neutral variation, where the change doesn’t give the organism an advantage or disadvantage. This is one way that differences can accumulate over time because there is no mechanism to weed out these benign mutations. However, a mutation will bestow the organism with a survival advantage. And this is rewarded with a higher likelihood of survival and reproduction.
Genetic variation in the gene pool will always occur. But there must be some external factors present for evolution to occur. Mutations will only increase in a statistically significant way if the organism receives a higher probability of survival and procreation.
We can use the Hardy-Weinberg equation to determine whether evolution is occurring in a population. When evolution is not occurring, all alleles and genotypes will reoccur with the same frequency, a situation we call Hardy-Weinberg equilibrium.
Hardy-Weinberg equilibrium, P² + 2PQ + Q² = 1, P + Q = 1.
For a particular trait with a dominant and recessive allele. We represent the dominant allele frequency with P and the recessive allele frequency with Q, So P + Q = 1.
The three genotypes must also add up to one. So if we make a Punnett square, we should expect that the frequency of homozygous dominant, or P squared, plus twice the frequency of heterozygous, or PQ, plus the frequency of homozygous recessive, or Q squared, will add up to one, P² + 2PQ + Q² = 1.
These are the only three possible genotypes and P, Q values to get each genotype’s probabilities. These numbers will remain constant if there are no mutations. Natural selection is not a factor, the population size is large, and there is no gene flow. These parameters are characteristic of a system in Hardy-Weinberg equilibrium.
In such a case, measuring the frequency of any genotype allows calculating the others, as they must add up to 1. But when one of these assumptions no longer applies, the population is indeed evolving. The direction of the fluctuation can offer clues as to the mechanism at work.
Gene flow, on the other hand, occurs because of the movement of fertile organisms. Gene flow is the movement of an individual or the gametes from one place to another. It’s also known as migration. This way, the influx of alleles into a population can cause the allelic frequencies to change from one generation to the next. It is the very definition of evolution. When looking at species with migratory habits, like many birds, alleles are transferred in or out of the gene pool due to this behavior.
Gene flow even occurs in humans, as it has become increasingly common for people to move across the globe. So mating between different populations is typical, whereas it was pretty rare even just a couple of hundred years ago. But natural selection is the only guiding hand to evolution that is not random. It is predicted that beneficial adaptations will be passed on, which slowly produces brand new species. This can work in a variety of ways.
These mechanisms are different ways by which evolution proceeds, which are all encompassed under the term microevolution. It means evolution below the level of species. For example, Galapagos finches adapt to the available food source without the Finch population becoming a new microevolution species. Many creationists will agree that this evolution exists, noting the variation in breeds of dogs or horses. But they categorically refuse to acknowledge that macroevolution happens too.
There is also intrasexual selection, typically among males, who in many species will fight over females in ritualized displays, including humans. Apart from sexual selection, there are forms of balancing selection, whereby variation in the genome is preferred, such as the heterozygous advantage. This is strict regarding the genotype and not any particular phenotype. There is selection related to avoiding predators, matching climatic conditions, and all kinds of other factors. But with all this, we must recognize the limitations of natural selection.
Importance of evolution
Evolution helps us to understand the history of life. Human biology is only scratching the surface of why the study of evolution is essential. Animals don’t have thumbs! Humans and primates are the only animals to have opposable thumbs. This was useful when humans developed and used tools. This trait has come from evolution. There have been millions upon millions of species past and present.
Yet natural selection requires death, extinction, random variation, and non-random selection to innovate. It is a process that takes an arduous amount of time – small changes, generation after generation, and ultimately epoch after epoch. The Latin name for our species, Homo sapiens, means “wise man,” an arrogant name to give yourself. But it isn’t just “wise” that has led to the massive rise of complexity in human societies over the past 250,000 years.
The importance of evolution:
- The survival string will develop, and this creates a strong species.
- The body structure will develop to live long, and the stronger can reproduce more.
- DNA mutation and natural selection can create more variant species that also create diversity.
The theory of Evolution doesn’t tell us exactly how life began on earth, but it helps us understand how life goes on. It also helps us make sense of how modern creatures continue to adapt and change today.
“Evolution Resources.” Washington, DC: National Academies of Sciences, Engineering, and Medicine.
Futuyma & Kirkpatrick, Chapter 4: Mutation and Variation
Voet, Voet & Pratt, Chapter 1: Introduction to the Chemistry of Life
Lewontin, Richard C. “The Units of Selection.” Annual Review of Ecology and Systematics.
Futuyma & Kirkpatrick, Chapter 1: Evolutionary Biology