Evolution history-common ancestry

Evolutionary History and Relationships Explained


What is evolution? Evolution is a change in the genetic makeup of an organism over time. All living things share a common ancestor, and this process has been occurring for billions of years. The measure of similarity between two organisms can be determined by comparing their DNA sequences.

When organisms have similar DNA sequences, they are more closely related than if they have different DNA sequences. We use phylogenetic trees to show these relationships in detail and learn the history of life.

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How Does Evolution Work?

DNA is a sequence of nucleotides. All living things have DNA, and it encodes their genetic information, including the instructions for building proteins and other important molecules.

When an organism lives and reproduces, the sequence of nucleotides changes from one generation to the next. These changes occur due to mutations in the DNA. Most of these mutations do not cause any problems, but some can significantly affect the organism’s ability to survive in its environment or appearance.

Mutations that do not help the organism will usually be eliminated by natural selection. Those modifications that provide a benefit to the organism can become more common in the population.

Mutations are sometimes very specific to a particular individual, while other mutations can have more widespread effects on all individuals that carry it. For example, let’s say a gene encodes the instructions for making tails in all vertebrates (animals with backbones).

If this gene mutates to encode the instructions for making no tails, then all vertebrates in that lineage will be born without a tail. If a male and female inherit the mutation, they will be delivered without tails.

The changes in DNA from one generation to the next are known as evolutionary changes. They happen over time and lead to gradual changes in traits, such as body size or beak shape, that we see in the fossil record.

The rate of evolutionary change is not constant and can be influenced by environmental pressures such as climate, predators, or food availability.

Homologous Structures

Image: homologous structures

Organisms with different DNA sequences can sometimes have traits that are similar in shape or function. These shared features between organisms are often called homologous structures.

For example, bat and bird’s wings are superficially different because they serve other functions. However, the bones in their wing structures have similar shapes and functions in flight.

Homologous structures are classified into two groups: convergent features, where the same structure is present in different organisms, and analogous features, where a different structure performs the same function.

Some bird wings are convergent with bird feathers because they both serve as the bird’s primary mode of flight.

Analogous structures 

Image: Butterfly and Bat wings are examples of analogous structures

Analogous structures are found in organisms with similar functions but not necessarily related by common ancestry. For example, the wings of a fly, a beetle, and a hummingbird are all analogous structures.

Another example of analogous traits is the antennae of insects and flowers. When we see a similar trait between two organisms, it can be difficult to determine if it is convergent or analogous.

We look for shared ancestry to determine if it’s a homologous structure. We use other observations about the organism’s life and habitat to determine if it is convergent or analogous.

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Molecular Comparisons

Molecular comparisons can be used to show evolutionary relationships. For example, we can compare the DNA sequences of two organisms and look for differences in their nucleotide sequence.

We can also use molecular comparisons to identify sequences of nucleotides that are shared by two different organisms. If we find a series of nucleotides shared by both organisms, we know they are more closely related than if they had different sequences.

These comparisons can be useful if we know the function of a certain sequence. For example, if two organisms are more closely related to each other than they are to another organism with a different sequence, we know the function of that shared sequence.

We can also compare the proteins made by an organism to find similarities with other organisms. The advancement of DNA technology has made it possible to look at the protein sequences in detail and compare them with other organisms.

Comparisons of this type have revealed similarities between humans, apes, and other mammals.

What is Phylogeny and Phylogenic Tree?

Phylogeny is the study of evolutionary relationships. The word phylogeny comes from two Greek words that mean “tribe” and “study of.”

Phylogenetic trees are a type of diagram that represents evolutionary relationships between different organisms. They help us understand the evolutionary history of life.

A phylogenetic tree is a branching diagram that shows how different organisms are related to each other, both in terms of their common ancestry and their evolutionary changes. It’s also known as the tree of life on Earth.

Phylogenetic trees are often created using the DNA sequences of organisms, but they can also be made using other information, such as the structures or functions of an organism.

Why Study Phylogenetic Trees?

Phylogenetic trees answer the following questions:

  • What are some of the major evolutionary changes that have occurred in different groups of organisms?
  • Which group is more closely related to another, and how did they evolve from a common ancestor?
  • What are the evolutionary relationships between different living things?
  • How have the organisms evolved to survive in their environment?

Who Uses Phylogenetic Trees?

These trees are used by many different fields, including evolutionary biology and zoology. Scientists construct phylogenetic trees to understand the evolutionary history of life. For example, molecular biologists who study protein sequences can compare the structure and function of these proteins to find out the evolutionary relationships among organisms.

Other users of these trees are botanists, who study the evolution of plants and how they interact with different environments. Students also need to understand how a phylogenic tree works to understand the evolution of various organisms.

The Process of Constructing a Phylogenetic Tree

In building a phylogenetic tree, organisms are sorted into clades. A clade is a group of organisms that share an ancestor. The most recent common ancestor in the tree is called the last universal ancestor or LUA. The LUA is the ancestor of all life on Earth, so it had to be a very ancient organism.

A phylogenetic tree then traces the evolution from each clade to another. There are many tree-building methods, but we will focus on two of them: parsimony and Maximum Likelihood.

The parsimony tree is built by finding the most economical scenario for evolution to occur, given what we know about how organisms evolve from one another. This explanation means that the tree with the fewest evolutionary steps is built first, and any changes are made to it if they cannot be matched up easily.

Maximum Likelihood is different in that it builds the tree from what we know about how these evolutionary changes happen at a statistical level.

Each organism in a clade has an amniotic egg, so amniotic eggs are a characteristic of mammals.

What are the limitations of phylogenetic trees?

These trees have various limitations. For example, they may not be able to show evolutionary relationships among organisms that diverged too long ago.

Phylogenetic trees also only show evolutionary relationships among organisms. They can’t show differences between the members of a group, such as different types of cells or tissues within an organism.


Cladistics is one of the ways of determining evolutionary relationships among organisms. They are based on shared derived characteristics that organisms acquire during their evolution from a common ancestor.

Cladistics is used to define relationships between different organisms by looking for shared, derived characteristics inherited from a common ancestor.


A cladogram is a diagram that shows how different organisms are related to each other, both in terms of their common ancestry and their evolutionary changes. It’s also known as the tree of life on Earth.

Image : common ancestry-humans and apes

How Do Cladistics differ from a Phylogenetic Tree?

Cladistics differ from a phylogenetic tree in two ways:

– Cladistic relationships do not focus on shared DNA sequences, only on derived characteristics.

– Cladistics only looks at the similarities of organisms, while a phylogenetic tree looks for differences as well.

Visual Connection

In cladistics, visual connection refers to using the physical properties of organisms to make comparisons and generate hypotheses. In other words, it is a visual guide for understanding evolutionary relationships.

For example, when comparing grass blades in a field, it is possible to point out that the types of grass are closely related. The different shapes, colours, and sizes of the edges provide a visual connection for researchers to the group and classify species.

Even without scientific proof, visuals form an adequate basis to create a reliable hypothesis. After this formulation then it becomes easier to classify different organisms.


Taxonomy is the study of how different organisms are classified and labelled. One of the goals of taxonomy is to make sure that every organism has a scientific name. This name not only distinguishes it from other organisms but also identifies its genus and species.

Another goal of the taxonomic study is to make sure that all species are classified into a genus and sub-genus. The broadest classification is the kingdom. The Linnaean system of classification is one of the most commonly used and easiest to learn.

This system starts with kingdoms, divided into species or divisions, then classes, followed by orders, and finally families.

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Relationships Between Taxonomy and Evolutionary History

There are many connections between taxonomy and evolutionary history. For example, they both classify organisms based on their genealogy or lineage.

Taxonomic groups are grouped into higher-level groups, and these can be used to determine evolutionary relationships.

Taxonomic classification is based on the organism’s hierarchy, and it’s often used to determine evolutionary relationships.

Taxonomy is studying how organisms are classified, while evolutionary history explores how different species are related to each other.

Taxonomy can be used as a tool in evolutionary history, but it cannot replace the study of evolution itself.

The Concept of Natural Selection

Natural selection is the process by which individuals with certain heritable traits that make them more likely to survive and reproduce will pass on those desirable traits.

Charles Darwin first proposed the theory of natural selection in 1859. It has since been adopted as the universal explanation for evolution.

Natural Selection Mechanism

The mechanism of natural selection is based on the idea that all organisms produce more offspring than can survive in a given environment.

In every generation, the organisms that are best adapted to the environment will survive and reproduce.

As a result, they pass on their heritable traits to future generations of organisms, and in this way, adaptations evolve through natural selection.

Some of the benefits of natural selection are the following:

  • The ability to evolve helps organisms maintain their genetic diversity and adapt to changing environments.
  • Natural selection allows only the “fittest” to survive and reproduce.
  • It allows for the long-term survival of a species despite environmental limitations such as competition or food availability.
  • It allows for the natural selection of mutations.
  • Natural selection also helps organisms to maintain a balance between production and consumption.

How do relationships evolve – for example, the relationship between a parent and child?

If we look at the evolutionary history of this relationship, it can be traced back to when life first evolved. The relationships between parents and children evolved from asexual reproduction to sexual reproduction. Determining evolutionary relationships can be done in many ways, but the most common are based on molecular comparisons and phylogenetic trees.

Image : asexual and sexual reproduction

Why are some relationships more successful than others?

Some relationships are more successful than others because they have evolved to survive in their environment.

Different organisms live in different environments, and those that can survive in their environment are likely to be more successful than those that cannot.

Therefore, organisms that can survive in their environments will live and reproduce while other microorganisms die off.

Evolutionary Psychology

Evolutionary psychology is the study of how our evolved psychological mechanisms are designed to solve specific types of adaptive problems. These problems have recurred for human ancestors in the environment of evolutionary adaptedness.

Evolutionary psychology is a new field that has gained much traction in recent years, and it’s still growing.

It’s the study of how our evolved psychological mechanisms are designed to solve specific types of adaptive problems that recurred for human ancestors in the environment of evolutionary adaptedness.

One type of adaptive problem that our ancestors faced was the need to survive in a hostile environment where there may not be enough food to go around.

One example is the adaptive problem of finding a mate with good genes and resources to have children who will survive.

Therefore, natural selection would favour individuals who had a tendency to be attracted to people with better resources and genes because this was the best strategy for survival.

How to Choose the right relationships in evolution

If you want to know how relationships evolve over time, the first question is: “What type of evolutionary relationship are we looking at?”. Many types of relationships can be examined, including parent and child.

The evolutionary history of this relationship can be traced back to when life first evolved. The relationships between parents and children have changed over time from asexual reproduction to sexual reproduction.

Determining evolutionary relationships can be done in many ways, but the most common are based on molecular comparisons and phylogenetic trees. Accurately describing phylogenies is one of the ways of determining the right relationships. It is done through maximum parsimony.

What is parsimony?

Parsimony is the principle that all else being equal, hypotheses with fewer assumptions are better than those with more. This principle suggests that the simpler one is better for two phylogenetic trees and is usually applied in phylogenies.

The principle of parsimony helps in relationships because it is less complicated. If you try to decide which tree has the fewest assumptions, the simpler one is likely to be the better selection.

What is Horizontal Gene Transfer?

Horizontal gene transfer is the transfer of genetic material between unrelated individuals. The introduction of foreign DNA into an individual’s genome can positively or negatively affect an organism’s fitness.

Negative horizontal gene transfer (HGT) is when foreign DNA introduces a mutation with no selection for the organism.

Positive horizontal gene transfer (HGT) is when foreign DNA introduces a mutation that selects the organism.

This transfer explains why some bacteria become resistant to certain antibiotics over time. It occurs in three stages, namely: Transformation, transduction, and conjugation.


Transformation is the first stage of horizontal gene transfer, and it occurs when bacterial DNA enters other bacteria via a process called transformation.

Foreign DNA will then enter the cell, and if it is not destroyed, the bacteria will produce copies of that DNA. This process can happen when there are environmental stresses on the bacterial cell.

It may also happen when the DNA is close to other bacteria (such as on a food particle). The type of stress that will cause the transformation to occur can be physical, chemical, or biological. The foreign DNA may end up in a new location and disrupt an existing gene.


Transduction is the second stage of HGT, and it occurs when a bacteriophage or plasmid transfers DNA from one bacterial cell to another.

It is a process that involves the movement of DNA between bacteria that are not related to one another, and it can happen in three ways:

  • through an infected cell,
  • plasmid transfer between cells in coexistence, or
  • by a DNA virus.

This process can happen when a coexistence of bacterial cells and the plasmid DNA (which contains only a few genes) is transferred between cells.

The DNA may get transferred to a bacterial cell that does not have the phage or plasmid, and these two will coexist.

Transduction can also happen when a phage particle or plasmid that has been injected into one bacterial cell will infect another.


Image : DNA transfer

The third stage of horizontal gene transfer is conjugation. This process happens when two bacteria are in contact, and their plasmid DNA will then be transferred to one another.

In this process, a plasmid is introduced into the recipient cell by way of an appendage called a sex pilus.

The transfer of DNA between bacteria is important because it can help with antibiotic resistance and the evolution of different bacterial species.

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Final Remarks

The evolution of the human species is just a small part of the story. There are so many other interesting aspects to explore and learn about that we encourage you to research further on your own! We’ve covered some core principles in this article.

There’s still much more information out there for you to explore. Other sources will give you an even better understanding of how different organisms have evolved and why they might be doing what they do today. Also, our professional biology writers can do it for you in case you do not know where to start.

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