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The theory of organic evolution roughly puts it that all living organisms as we currently have them on earth came as a result of descent from a common ancestor, even though not without varying degrees of modification. The modification has been hypothesized to have resulted from changes in the environment where organisms reside. As the environment changes, living organisms change along with it in order to ensure continued survival and reproduction.

<center>![](https://cdn.steemitimages.com/DQmXLw7WC6ctjAHSYsWea26KYpbVRroseeeX7wrw32FgA3D/image.png)</center>
<center><sup>source: [flickr](https://www.flickr.com/photos/spidermandragon5/2922128673)</sup></center>
As a result of the continuous quest to change with the environment, organisms acquire some abilities which were not inherent in them from births. Some of these abilities become embedded in the genomes of the organisms and are inherited by their progenies. The process of changes and diversifications from a single ancestral species to different forms as a result of changes to the environment is what evolution biologists refer to as adaptive radiation. This simply means that different species from a single ancestor come into existence by taking different lines of adaptive radiation.

The evolution of man results from a unique adaptive radiation and evolutionists believe that the ancestors of man are the fishes. Life is opined to have arisen from the aquatic environment and as events kept catching up with the water bodies, aquatic organisms started developing features which eventually enabled them to survive on dry land but not without major morphological and genetic changes to their bodies.


Man belongs to a division of animal known as the Chordates. All animals within this division have some peculiar characteristics which indicate that they must have evolved from a common ancestor. Some of the most prominent features include the possession of notochord either throughout or at some point in their life cycle, possession of dorsal hollow nerve cord, a pharyngeal gill silt and a post-anal tail. The animal division is further sub-divided into two namely; the invertebrate chordates otherwise known as protochordates and the vertebrate chordates. While the protochordates include the urochordates and the cephalochordates, there are five different classes of animals within the Vertebrates - two fish classes (Chondrichthyes and agnatha), amphibians, reptiles, birds (aves) and mammals.


The jawless fishes were reported to have been the first to evolve about 530 million years ago. From the jawless fishes which are now extinct, the jawed fishes evolved about 485.4 million years ago. Millions of years after (about 365 million years ago), a wide variety of fishes have evolved through different adaptive radiations and from one of them (the lobe-finned fishes, aka Sarcopterygii), the four-limbed vertebrates evolved. The amphibians were the first tetrapod to evolve and also the first to live successfully away from the aquatic environment even though they could not reproduce without water. Hence, they live on land and return to water during their reproductive periods.

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<center><sup> Evolution of jawless fishes from the Cambrium to the present. Image By Epipelagic - Own work, CC BY-SA 3.0, [link](https://commons.wikimedia.org/w/index.php?curid=24501994)</sup></center>

About 65 million years after, the first set of vertebrates whose existence is independent of the aquatic environment evolved from the amphibians. The reptiles are able to fully exist on land without having to go back to water for reproduction. Birds and mammals evolved from reptiles through different adaptive radiations.


Mammals happen to be one of the biggest class in the animal divisions. They are currently being represented by 3 major sub-classes and about 27 orders. Out of the 3 sub-classes which include the eutherian, the metatherian and the monotremes; the eutherians which are otherwise known as the placental mammals are the most diverse and widespread with about 20 orders. Primates are the most interesting in the group because humans have been hypothesized to have evolved from them, not without some evidence.


Evolution continued to take its toll and engineered changes within the primates with two groups (the proto-primates and the true primates) taking separate adaptive radiations line and paying their dues along the way. Proto-primates became extinct but the true primates continued their journey upward the evolution ladder with larger brains, eyes and muscles playing important roles before eventually diverging into old world monkeys and new world monkeys.


Those that are familiar with human evolution must have heard about the ancestor of man being the apes. The apes evolved from the old world monkeys and as time went by, they became distinct into two groups - the lesser apes which include the gibbons and the greater apes which include the gorillas, the chimpanzees, the orangutans and the early man. One of the most important changes that brought about the first human species is migration from quadrupedalism to bipedalism. From the greater apes to australopithecines which are generally believed to be the first Hominin and up to the modern day humans (Homo sapiens), evolution proceeded both biologically and socially.

<center>![](https://cdn.steemitimages.com/DQmdTpdzZvxn5rWNh3aCHSzY1EPFaR1BvxyYvSvRr5KTKcP/image.png)</center>
<center><sup>A family of old world monkey. Image from [pixabay](https://pixabay.com/en/green-monkeys-monkey-112275/)</sup></center>

Changes from primitive man to the present day man have been largely attributed to a lot of factors with the development of brain taking a center stage. The primitive man is believed to have thrived on raw fruits/leaves gathered within the forest and raw meats gotten from hunting games. The successful attempt to tame wildfires represented a turning point both in socio-cultural and biological evolution that eventually gave rise to modern man. Fire enabled primitive man to be able to extract more nutrients from his food through cooking and this led to the development of bigger brain which significantly improved their cognitive and tools developing skills.

It has been found that the brain of primates is about twice the size of the brain of other mammals of the same body size and this has been narrowed down to the consumption of more nutrients by true primates. Recent observation, however, reveals that the brain of the modern day *Homo sapiens* is actually smaller as compared to their early *Homo* predecessor and this has been attributed to limited nutrition in agricultural populations. The observation was further reinforced with rebound brain size witnessed in children growing up in industrial societies with adequate essential nutrients.

*Do you think the modern man would still evolve? What do you think we would evolve into? Feel free to engage me in the comment section.*

Thank you all for reading.

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### References

* [Wikipedia: Adaptive radiation](https://en.wikipedia.org/wiki/Adaptive_radiation)
* [Sciencing: Five classes of chordates](https://sciencing.com/five-classes-chordates-8145209.html
)

* [Wikipedia: Evolution of fishes](https://en.wikipedia.org/wiki/Evolution_of_fish)
* [Lumen learning: Evolution of primates](https://courses.lumenlearning.com/boundless-biology/chapter/the-evolution-of-primates/)

* [Scientific America: How Has the Human Brain Evolved?](https://www.scientificamerican.com/article/how-has-human-brain-evolved/)

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