Human Evolution: History, Timeline, and Future Predictions

Quote by V. S. Ramachandran
The human evolutionary tree is a complex structure, branching and re-branching at several points along the timeline. Though a complete study of human evolution is beyond the scope of one article, it endeavors to highlight the main stages, and also tries to makes predictions about the next step in the ongoing process of human evolution.
Did you know?
All males amongst modern-day human beings possess a Y chromosome inherited from a male that lived in Africa about 140,000 years ago.
The story of human evolution isn't just a single tale. It is actually a collection of several short stories, each connected to the other like the links in a chain. The human tribe, or the hominini, has evolved over millions of years, from creatures you would scarcely imagine to have anything in common with. We are the result of the adaptive evolution of several different species. Thus, in essence, within each of us, you can find the ghosts and spirits of many ancient animals of the past.

But we humans are basically primates, and therefore, our history must have more to do with that of the monkeys or the chimpanzees, than say, for example, a fish. We have the same five fingers, the same front-facing eyes, and even have similar behavior and habits as them. But believe it or not, humans, monkeys, chimpanzees, and indeed all the animals that we see around us today were all fish once living in the oceans. Therefore, in order to learn about our past, we have to learn about not just the monkey, but also the fish inside us.

So let's take a journey through the sands of time and let the tale unfold. This is the fascinating story of our bodies, and why we are built the way we are. This is the story of human evolution.
The Story of the Fish That Walked 400 MYA - 350 MYA
Dakosaurus profile
If I were to tell you that your earliest ancestor was a fish, would you believe me? Of course you won't! A monkey maybe; but a fish, no way! However, in all probability, that theory is true, and the evidence for it is present right there in your hands.
It is a widely accepted fact that life on earth began in the oceans. Nearly 3.6 billion years ago, the first living things in the form of simple celled organisms first appeared in water. These simple cells later combined to form multi-cellular life forms almost 1 billion years ago, and soon the oceans were swimming with all kinds of living things, including various fish, aquatic plants, etc.

Then, close to 365 million years ago, some ancient fish used their fins to crawl out of the oceans onto the lands. In order to move there, their fins evolved into feet and claws of reptiles, which later evolved into the paws of mammals with short fingers all pointing the same way. As these mammals spread over the lands and began living in various habitats, they evolved further, and finally their claws became hands, as these primitive mammals evolved into the first primates we are all the descendants of.
The Tale of Notharctus Tenebrosus 54 MYA - 38 MYA
Notharctus lived 54 to 38 million years ago. Though from its first fossil discovered in 1870, it was thought to be a member of an obsolete order of the mammalian family, the later discovery of an almost complete skeleton firmly established it as being a primate. It lived high up in the canopy of large ancient trees.
Notharctus is linked with humans, because it shared with us a unique characteristic - the opposable thumb. Life in the trees caused the lengthening of its fingers and the addition of an opposable thumb in order to allow it to reach the edible flowers and fruits growing at the ends of thin branches.

Northarctus Tenebrosus had large hind limbs, and a tail which helped it to balance itself on the branches of trees. It must have had a body weight of around 10 lb, and from head to tail would have been nearly 40 cm long.

Notharctus and the following species which lived amongst the foliage provided us with another important characteristic - our color vision. Early primates saw only a limited range of colors, but then one group developed full red green and blue (RGB) vision, to distinguish the ripe fruits from the green unripe ones. Thus, we not only owe our ability to grasp (opposable thumbs) but also our full color vision to the lives led by Notharctus and our early ancestors high up on the trees.
The Tale of the Elusive Ancient Primate 8 MYA
According to studies, modern-day humans share 98% of their DNA composition with chimpanzees. This fact indicates that our race and that of the chimpanzees must have had a common point of origin. In fact, many theories suggest that the human tribe, or the hominini, and all the other species and subspecies within our genus, including the modern-day apes such as gorillas and chimpanzees must have all descended from the same ancient primate.
However, fossil-based evidence hasn't been able to substantiate this theory, and perhaps it never will, because of the complexity involved in the classification and establishment of the relationship between the fossils of the numerous ape-like creatures of the time.

This elusive ancient primate, our common ancestor, must have evolved from the Notharctus species, and is believed to have existed 8 million years ago.
The Tale of Ardipithecus Ramidus - The Bipedal 5.6 MYA - 4.4 MYA
Australopithecus africanus
For several years, anthropologists had believed that bipedalism (the human ability to walk on two legs) was developed in response to changes in the habitat of our ancestors from woodlands to grasslands. However, the discovery of a new species - the Ardipithecus Ramidus in 1994, turned that theory right over its head.
Ardipithecus Ramidus lived mainly on trees, as is evidenced from its bone structure. However, the discovery of its skeleton showed that it had a hip bone structure which is remarkably similar to ours. Studies have concluded that such a hip structure must have enabled it to walk upright, though the reasons for it to do so are still unknown. One theory suggests that it must have stood up to have a larger field of vision while on ground where it must have felt less safer than up on the trees.

The Ardipithecus lived in the African continent, was 4 ft tall, and a good climber. It used all four limbs while on trees, but stood upright to walk on the ground. The members of this species also had smaller canines, which is another indicative factor towards our common lineages. However, another species was found that lived about the same time as Ardipithecus Ramidus, and which too was bipedal,. This discovery has since had many anthropologists debating about our relationship to it, with some even questioning whether Ardipithecus was even a hominini at all!
The Tale of 'Lucy' in the Ground with Earthworms 3.2 MYA - 1.7 MYA
Skeleton of lucy
In 1974, the fossilized remains of a female primate was found in Ethiopia. She was named Lucy, after the Beatles' song Lucy in the Sky with Diamonds. Dating methods indicated that Lucy lived 3.2 million years ago. Another excavation in 1978 showed distinct tracks of human-like footprints made by members of the same species, walking on two legs (bipedal). This species was named Australopithecus aferensis, after the people and the land of Africa.
Thus, it is now believed that the single line of evolution from fish to reptiles to mammals and finally to primates must have branched off into two different lineages, nearly 6 million years ago. One ultimately leading to the gorillas and the chimpanzees of present day, while the other to modern-day human beings.

Many believe that the first in the human line of evolution was, not the Ardipithecus, but the Australopithecines, which lived in the continent of Africa nearly 3 million years ago. Just like the Ardipithecus, the members of this species displayed several distinct characteristics linking them to modern-day human beings, the most significant of which was the development of bipedalism, or the ability to walk on two legs.

The Australopithecines show skeletal features distinct from other primates and closer to that of modern human beings. They had a greater forearm-to-upper arm ratio as compared to other hominids of the time, and exhibited increased sexual dimorphism. Fossils reveal that the average height of adults was up to 1.5 meters (4.9 ft), and their weight was nearly 120 lb. Skull fossils indicate that their brains had a volume of about 600 cc.

Australopithecines later subdivided into various subspecies, including Australopithecus anamensis, A. sediba, A. africanus, and A. afarensis, with each showing subtle differences compared to the other. All these sub-subspecies thrived in various parts of the continent of Africa, till they finally became extinct almost 2 million years ago.
The Complex Story of the Homo 2.58 MYA - Present
Homo habilis
Whether it was the Ardipithecus Ramidus or the Australopithecines, it is still unknown. But one thing is for sure, it was one of those two species that evolved into the final link in our chain of evolution - the genus Homo.

The long and complex homo lineage first began around 2.4 million years ago. Tracing the entire line along with all its branches down to us and establishing a relationship between each link is an almost impossible task. There are many species and subspecies within the genus homo which could or could not be related to us. The scientific opinion too, in this matter, is divided into many different camps, leaving us with the single option of detailing only the most significant members of this genus.
Homo erectus and fire
Among the earliest members of the homo genus were the homo habilis. These primates were very resemblant to the Australopiths in a number of ways. For instance, they too had long hanging arms. However, unlike the Australopiths, they had smaller teeth and much more human-like arms and feet. Their faces too were less protruding. They were short in stature, and had a brain size of 510 cc, which is roughly less than half the size of ours. Many homo habilis findings are accompanied with stone weapons, which points towards the development of mental capacity and intelligence. They lived in Africa nearly 2.33 million years ago.
Male and female homo erectus
Homo ergaster, or the African homo erectus, succeeded H. habilis. Their physical constitution evolved to be more nearer to modern human beings, but their brains, though larger than the H. habilis, were still smaller than ours. They are estimated to have been over 6 ft in height, with a less protrusive forehead, and smaller jaws and teeth. They had longer noses with downward-facing nostrils. They also had significantly larger brains compared to H. habilis, with skull findings pointing towards a cranial capacity of nearly 900 cc.

The H. erectus species thrived and existed for almost 1.5 million years. During this large span of time, they migrated out of the African continent and spread to other continents, including Europe and Asia, as is evidenced by their fossils found there. Homo erectus were also the first primates to use fire and hunt with weapons.
Human evolution of the skull
Lastly, in the final stages of human evolution, the neanderthals and the homo sapiens came into existence about 200,000 years ago. Both these species developed complex brain structures, and gave birth to language and culture, and their later members began to wear clothes.

Homo neanderthalensis, or the neanderthals, were very similar to modern-day human beings, with their DNA differing from ours by just 0.12%. They had larger brains than ours (1,600 cc), but at the same time had a larger bodily structure as well. The last of the neanderthals died out in Europe close to 40,000 years ago.

Early homo sapiens had nearly the same brain size as that of ours (1,350 cc), but had characteristic thick skulls and a prominent forehead. The rest of their anatomy was nearly similar to that of ours. Homo sapiens is the last surviving species of the genus homo, and modern-day human beings, or the homo sapiens sapiens are its subspecies.
The Untold Story of the Man From the Future In the Future
Human kind has come a long way. We were fish once, and now we eat fish for dinner! Our evolution has been phenomenal. So what does the future have in store for us? What evolutionary changes will modern-day human beings undergo? What will they look like in the future?

These certainly are interesting question, albeit, not very easy to answer. Making random predictions about the future can be dangerous. The great fictional detective Mr. Sherlock Holmes says, "I never guess. It is a shocking habit, destructive to the logical faculty". However, when on a difficult case, often, he too would dare to predict, provided that there were enough facts to support his assumptions. The future of human evolution is one such challenging mystery. So, following the lead of Mr. Sherlock Holmes, in the following few lines, we too shall dare to predict the future evolution of present-day human beings, based on as many facts as we can gather.
Loss of Muscle Mass: Present-day humans hardly get any exercise. The majority of us live very sedentary lives. Thus, it is quite possible that future humans will have significantly less muscle mass, and will rely on machines to do all the physical work.
Increased Myopia (Nearsightedness): Our ancestors lived in the wild. They required a large range of vision to scour the landscape. But, with most of us migrating to the cities, and with our cities getting more and more congested, we are hardly ever required to see more than 20 ft. away. This problem is more likely to escalate in the future. Thus, it is safe to assume that in the future, our myopia will increase and our hyperopia (farsightedness) will decrease.
Increased Skull Size: The muscle that works the most is the muscle that grows. This fact foretells that, considering that modern-day humans use their brains a lot more than older generations, it is quite possible that future humans will have increased skull size to accommodate their gigantic brains.
Lower Immunity: Advanced medicines of the future will enable us to fight off diseases much more efficiently than our natural immune system. Therefore, in the future, we will no longer need to have an immune system to protect us.
Racial Uniformity: Our ancestors originated in Africa, and later moved to various other continents, including Asia, Europe, Australia, and America. The different environmental and climatic conditions of these different regions caused them to undergo further physical changes, and this gave rise to different races and ethnicity. But thanks to the advances in the modes of transportation and communication, the world is becoming one again. With modern human society becoming a mixture of people of different ethnicity intermingling and living together, it is quite in the books that in the future, the lines of distinction between various races shall blur, and future human beings will most likely go back to being one uniform race again.
Lesser Teeth and Smaller Toes: Fossils of feet show that our ancestors had wider feet with longer and spread toes. But since hardly any of us goes about barefoot anymore, it is likely that in the future, our feet will be smaller with shorter toes. Also, since we ingest only cooked food, which is softer and hardly requires any chewing, possibly in the future, humans will have very small teeth.
Taller and Balder: Humans today are better fed and protected against the elements of nature. Thus, our descendants are most likely to grow taller as well as have lesser hair on their bodies.
Increased Life Expectancy: "And when he shall be immortal, he shall become a God." ―Anonymous. Though immortality might still be a distant dream, humans of the future will definitely live longer and better lives, just like we do when compared to our ancestors.
Selective Evolution-playing God: With all the terrific advances in science, especially in the field of genetic engineering, parents in the future will literally be able to 'manufacture' their children based on their personal preferences.
So, there you have it, a collection of short stories, which when combined together, form the single great tale of human evolution. We have come a long way, and the journey until now has been more than just exciting. From a single cell floating in the ocean waters, we have managed to become the multi-cellular wonders of nature that we are today. Where we will go from here, predictions apart, only time can tell.