The one about Human Evolution
We are used to thinking about ourselves as the only humans because that’s how things have been like over past 12,000 years. But life used to be very different for millions of years before with many different species of us humans roaming the earth. About 200,000 years ago modern day humans joined the party. And since then every other species under the Hominidae family has gone extinct and only one remains — Homo Sapiens.
The cradle of humankind, said Darwin, was Africa. His reasoning was simple:
In each great region of the world, the living mammals are closely related to the evolved species of the same region. It is, therefore, probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee: as these two species are now man’s nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere.
We have to remember that when Darwin wrote these words, no early human fossils had been found anywhere; his conclusion was based entirely on theory. The fact that this is true is evidence of Darwin’s brilliance.
Technically we can trace any evolutionary story back to the origins of DNA itself and formation of cyanobacteria (fossilized evidence above), the first life on Earth about 3.8 billion years ago when our Earth was 700 million years old. From that first DNA came the entire diversity of life on earth. So, the last common ancestor of humans and chimps existed about 10 million years ago, but the last common ancestor between us and crows existed 320 million years ago, and last common ancestor between us and bacteria existed 3 billion years ago. But I will start the story of our human ancestry with the entrance of first primates about 65 million years ago, right after the age of dinosaurs ended. In this blog you will learn how we went from the emergence of first primates to modern day humans capable of complex thoughts and emotions. Before I start the story, let’s go over some basics.
DARWIN’S ORIGIN OF SPECIES
Darwin’s 1859 best seller Origin of Species book had two theories. One is that all species of life on Earth have arisen from other pre-existing species. The second in that the process that drives evolution is natural selection: some individuals in a population have more offsprings than others; offspring tend to inherit the attributes of their parents; so later generations contain more of the sort of individual that, in previous generations, left more offspring. The individuals who leave the most offspring tend to be best adapted to the local conditions. So natural selection causes living creatures to evolve to be well-adapted for life. Some attributes, such as a peacock’s tail or the antlers of a stag, appear not to help living creatures survive the rigors of the environment but to help them compete to attract members of opposite sex. Darwin later published a book explaining these attributes by the theory of sexual selection — a special case of natural selection. Individuals (usually males) compete against each other for a limited number of mates, rather than for limited environmental resources.
TAXONOMY
An organism’s taxonomy helps us trace its lineage back to the beginning. This is what a Homo Sapien’s taxonomy looks like:
The first category is Domain (not shown in diagram above). We belong in Domain, Eukarya. Other domain is Bacteria. First eukaryotes came about 2.7 billion years ago. Under Eukarya, we belong to Kingdom, Animalia. Other Kingdoms include Plant and Fungi. Amongst the animals, we belong in the Phylum, Chordata. Chordata represents all vertebrate animals. First chordates came about 530 million years ago. Of all vertebrates, humans belong to the Class of Mammalia. First mammals came about 200 million years ago and lived in the shadows of dinosaurs. Some of the mammals evolved into primates about 65 million years ago.
Then about 10 million years ago, the Hominidae family that gave birth to modern humans split from chimpanzees. First Homo genus evolved in East Africa about 2.5 million years ago from an earlier hominin (same as hominidae) called Australopithecus. Some of the species ventured off to Europe and Asia and evolved separately with different traits. For example, Homo neanderthalensis who lived in Europe and western Asia were bulkier and more muscular than us as they evolved in harsher climates. Homo erectus (upright man) evolved in eastern Asia and hold the record for longest surviving homo species. Humans have been around for merely 200,000 years when compared to over 2 million year survival rule of Homo erectus. One of the species that remained in Africa gave birth to the first Homo sapiens about 200,000 years ago.
Animals are said to belong to the same species if they tend to mate with each other, giving birth to fertile offsprings. Mutations in DNA usually only crossover within the same species. Now, this is mostly true but there are exceptions. Like some wild dogs and wolves have been observed to mate. And our own species of humans mated other species including Neanderthals and Denisovans. In fact, most humans have 1–4% neanderthal DNA. What defines a species may soon need revision.
Species that evolve from a common ancestor are grouped together under the heading “genus”. For example, lions, tigers, leopards and jaguars are different species under the genus Panthera. But a german shepard and a chihuahua are the same species collectively known as Canis familiaris.
What characterizes as a primate?
Primates arose from small terrestrial mammals with adaptations to live in trees. This was an extremely helpful adaptation as it protected primates from land dwelling predators. Primates, like all humans, have opposable thumbs that allowed them to grab the tree branches easily. To understand what opposable thumbs mean, try grabbing things without using your thumbs. Primates also developed more complex forward-facing visual systems that gave them depth perception. This is important if you are jumping from one branch to another so we don’t fall off. Primates also have a higher degree of shoulder mobility compared to other animals. Other than these traits primates also have flat nails, upright torsos, pendulous penis, and grasping tails.
The Cretaceous — Paleogene Mass Extinction
About 66 million years ago, Earth was hit with one of its several mass extinctions. This particular event was caused by impact from a massive asteroid or comet. Both the mass extinction and its cause are evidenced by a layer of earth known as the K-Pg boundary which is found all across the continents. It’s a dark colored boundary dating 66 myo and containing high levels of iridium. Iridium is rare on Earth and is found in abundance on asteroids. Extensive fossils are found before this boundary and none beyond. The impact location is known as Chicxulub crater in Mexico.
Animals that were able to fly off, bury in ground, or dive in oceans were able to survive this extinction event. The dinosaurs that could fly are direct ancestors to the birds we see today. Small primates the size of rodents burrowed underground and are the direct ancestors of us humans. One’s already living in oceans survived and other amphibians like turtles and some mammals went back in oceans.
THE FIRST PRIMATES
About 70 million years ago, one group of mammals branched into two groups: Dermoptera and Primates. Dermoptera includes mammals like flying lemurs (not really lemurs) and are the closest non-primate relative to us. The Primates branch over next several million years and split in 3 different branches: Plesiadapiformes, Strepsirrhini and Haplorhini. Us humans, chimpanzees, apes etc belong to the Haplorhini branch.
PLESIADAPIFORMS
Plesiadapiformes first appear in the fossil record between 65 and 55 million years ago, although all groups directly assigned under this order are extinct today. They had primate grasping hands and feet, but were still primitive with a small brain. They were the size of a mouse and lived in tress, feeding on flowers and fruits. Up until 56 million years ago, plesiadapiforms were the only primates. Shortly afterward, fossil strepsirrhines and haplorrhines appeared and rapidly began to diversify.
STREPSIRRHINI
Strepsirrhini fossils have been found in Europe, North America, Africa, and Asia. They are defined by their wet noses unlike the dry nosed haplorrhines. Modern strepsirrhinis include lemurs, lorises, and galagos.
HAPLORRHINES
Haplorrhines are divided into tarsiers and simians. Simians include Old world monkeys and New world monkeys. Modern day humans evolved from the Old world monkey branch of haplorrhines.
NEW WORLD MONKEYS
Some of the simian monkeys split off about 40 million years ago and lived on the isolated continent of South America. These include modern day spider monkeys, howler monkeys, woolly monkey, uakari monkey etc. A broad nasal septum with nostrils on the sides differentiate them from the old world monkeys that birthed humans and apes.
OLD WORLD MONKEYS
They live in Africa and Asia, mostly in the tropics, but some range into snowy climates in Japan and the mountains of western China. Modern day baboons and macaques belong in this group. They have front facing nostrils (like us). But unlike us they have cheek pouches to store food.
Hominoids (apes and humans) split from old world monkeys about 30 million years ago.
GREATER AND LESSER APES
The Old world monkeys gave rise to two lineages: Greater and Lesser apes. One of the biggest difference between these apes and old world monkeys is a lack of tail. Lesser Apes gave birth to gibbons. Greater Apes split in two different lineages with two different common ancestors: Sivapithecus and Dryopithecus. Chimpanzees, gorillas, and humans descended from dryopithecus. Its Asian contemporary, Sivapithecus, gave rise to orangutans.
All great apes exhibit skills and intelligence way beyond the capabilities of monkeys or gibbons. They make complex nests for sleeping in at night. They practice strategic planning in their social lives. When tested in laboratories, great apes can solve complex psychological problems. They can also recognize themselves in mirrors — like humans they are self aware. Here are some examples of the great apes using self made tools:
Genetically, humans are closest to chimpanzees and, reciprocally, chimpanzees are closer to humans than gorillas. There is only about 1 percent difference between our DNAs. We diverged from chimps around 10 million years ago.
Interesting thing about our chimp ancestry:
Chimpanzees live in a male dominant social hierarchy which is full of conflicts, aggression, bullying and even killing of each other. Their close relative, Bonobos on other hand live in a extremely peaceful female dominant hierarchy. If two groups of bonobos meet for the first time, they are more likely to form friendships than start a war. Chimpanzees on the other hand will fight till only one alpha male remains. Kind of makes you wanna wish we descended from bonobos instead :)
HOMININS
The term hominin describes living humans and all other species comprising the lineage that diverged from that of chimpanzee about 10 million years ago. The hominin fossil record is currently made of 24 species with modern day humans being the only species still alive today. It’s important to understand that this is not a linear evolutionary model. At any given point several different species of Homo genus resulting from different lineages existed on Earth. Only some of these species are our ancestors and rest became extinct without giving rise to new species. Last species to go extinct was the indonesian Homo floriesiensis about 12,000 years ago.
Savannah Hypothesis: emergence of grasslands and arid landscapes pushed some chimpanzees to abandon trees to go explore. Upright walking, it is suggested, was the most efficient way of moving over open grasslands, with the added benefit that it freed the hands for carrying items or for making tools. Upright walking also gave them better vision that helped in seeing danger in time to hide.
I won’t go over all 24 hominid species, but here are the most notable ones in chronological order:
Sahelanthropus tchadensis
AGE: 7–6 mya
LOCALITY: Toros-Menalla, Chad
FOSSIL RECORD: single skull, fragments of jaw and teeth
The first common ancestor of all hominids. A 7–6 million year old skull fossil nicknamed, Toumai (hope of life), was found in Chad, Africa.
Orrorin tugenensis
AGE: 6.2–5.6 mya
LOCALITY: Tungen Hills, Kenya
FOSSIL RECORD: jawbone, teeth, fragmented arm, thigh, and finger bones
Orrorin Tugenensis is possibly the first bipedal hominid. In 2001, fossils of arms and legs were discovered in Cheboit, Kenya. Several features of the femur (thigh bone) such as the round shape of the ball joint that fits into the hip socket and its orientation to the shaft suggest bipedalism
Ardipithecus ramidus-oldest hominid
AGE: 4.5–4.3 mya
LOCALITY: Aramis in Middle Awash, and Goma, Ethiopia
FOSSIL RECORD: One nearly complete skeleton; various skull, jaw, teeth, and arm fragments
The partial remains of 100 different individuals have been discovered, including an almost complete skeleton known as ARA-VP-6/500 or Ardi. They lived in open woodlands and foraged for fruits, nuts, and possibly insects. Scientists determine diets of extinct species by analyzing the thickness and molecular content of teeth enamel. Though bipedal, they also spent time moving around in trees.
Kenyanthropus platyops
AGE: 3.5–3.3 mya
LOCALITY: Lomekwi, Kenya
FOSSIL RECORD: skull, upper jaw, teeth
Kenyanthropus fossils were found along with hundreds of artifacts and stone tools. This is the earliest evidence of tool making. Human evolutionary tree had not even reached the homo genus yet when the first stone tools were formed. These primitive tools were possibly used to remove meat from the bones and smash them open for marrow.
Australopithecus afarensis
AGE: 3.7–3 mya
LOCALITY: Tanzania, Ethiopia, Kenya
FOSSIL RECORD: partial adult skeleton; nearly complete baby skeleton; complete knee joint; limb fragments; several mandibles
This species is considered to be the hominid that gave rise to our lineage. Fragmented remains of several hundred individuals, including males, females, and juveniles, have been found in East Africa. Among these were the fossilized remains of world famous australopithecus, Lucy. She is named after the Beatles song Lucy in the Sky with Diamonds, which was playing while the archaeologists celebrated their discovery. Her entire family of 13 individuals may have died together in a flash flood. Australopithecus were making stone tools as well.
This is also the first hominin species to leave behind well preserved footprints known as the Laetoli Footprint Trails. The tracks appear to have been made by three individuals. This also provided first evidence that bipedalism had started even before the arrival of first homo species.
Homo habilis
AGE: 2.4–1.6 mya
LOCALITY: Tanzania, Kenya, Ethiopia, South Africa
FOSSIL RECORD: several skulls, fragments of hand, arm, leg, and foot bones
Homo habilis (“handy man”) is the earliest member of the genus Homo to appear in the fossil record. This species is characterized by slightly larger brain, smaller molars and premolars, and more human-like feet than those of earlier hominins. They were the pioneers of Oldowan stone tool manufacturing which was later adopted by other species of homo genus. These tools were a bit more sophisticated than the older Lomekwi tools.
Olduvai Gorge in Tanzania is one of the most significant archaeological site. Spanning 30 miles long and 300 ft deep, it is composed of layers and layers of history. The site is divided into seven major beds, the oldest of which is Bed I including fossils Homo habilis fossils from 1.75 million years ago. The newest bed dates to 15,000 years ago. This site contains one of the most continuous record of human evolution making it invaluable.
Homo georgicus
AGE: 1.7–1.8 mya
LOCALITY: Dmanisi, Georgia
FOSSIL RECORD: skulls, lower jaws, fragments of upper and lower body
This is one of the first hominins to leave Africa. Remains of Homo georgicus were found on a single site in Georgia.
SUPPORTIVE CARE: A intriguing find at the archaeological site hints towards a supportive care environment amongst the Homo georgicus. A skull belonging to an elderly man showing signs of prolonged teeth loss was unearthed. When teeth are lost, the empty sockets within the bone resorb and create a scooped-out jaw shape like in the fossilized skull below. This particular man must have lived till old age and must have had a supportive social group to be able to manage without teeth.
Homo ergaster
AGE: 1.9–1.5 mya
LOCALITY: Kenya, Tanzania, Ethiopia, South Africa
FOSSIL RECORD: one nearly complete skeleton, few skulls, fragments of pelvis and limbs
The name Homo ergaster roughly translates to “working man”, a reference to the more advanced tools used by the species. This was the first species to show a modern humanlike body shape, stature, and limb proportions. Several sets of footprint trails found in Koobi Fora formation, Kenya show evidence that Homo ergaster had feet very similar to ours. A remarkably complete skeleton of an adolescent boy named “Turkana Boy” was discovered in 1984, Kenya.
This “working man” hominin made some of the most advanced tools of their times including handax. Hundreds of handaxes and other stone tools lie scattered across the ground at Olorgesailie, Kenya. Archaeologists believe that manufacturing of handaxes requires complex cognitive abilities. When neuroscientists recorded brain activity of human subjects making these tools, Broca’s area, the region in brain associated with language production was activated.
Homo erectus
AGE: 1.8 mya- 30,000 ya
LOCALITY: various sites in China, Java Indonesia
FOSSIL RECORD: one complete cranium, several incomplete crania, teeth, jaws, few limb bones
Known as the Java man, this is the longest surviving species of Homo genus. The first fossil was found on the island of Java in 1891 by Dutch army doctor, Eugene Dubois making it one of the oldest Homo species to be discovered (Neanderthals were the first). On returning to Holland in 1895, Dubois tried to persuade European archaeologists of this significance of his find. Not until the late 1920s was ‘Java man’ eventually accepted as an extinct human species, albeit not one originating in southeast Asia as Dubois believed. This was not an “asian version” of human species. Homo erectus originated in Africa, as Charles Darwin had suggested, and around 2 million years ago left Africa, reaching the Black sea by 1.7 million years ago and Java by 0.8 million years ago; here they perhaps survived until as recently as 27,000 years ago, coexisting with modern b humans.
TAMING FIRE: This was most likely the first species to tame fire which is evidenced by microscopic traces of wood ash found near Homo erectus fossils. They were also the first species to cook their food. Cooking food gave hominins a great advantage. They no longer needed big, strong jaws to chew through meat. Hominins that adopted cooking, eventually evolved to have smaller jaws and the extra energy was diverted towards a bigger brain.
Zhoukoudian caves in China have revealed some of the most important evidence of Homo erectus in Asia.
Homo heidelbergensis/rhodesiensis
AGE: 600,000–450,000 yo
LOCALITY: Kenya, Tanzania, Ethiopia, several sites across Europe
FOSSIL RECORD: a few complete skulls, fragments of jaw and limb bones
This species lived over a wide area from Africa(rhodesiensis) to Europe(heidelbergensis). Though initially considered to be two different species, they are now understood to be the same species. Few remained in Africa and few travelled to Europe. One’s that remained in Africa most likely are the direct ancestors of modern day Homo sapiens. One’s that left for Europe gave rise to Neanderthals, and possibly even Denisovans. This species had brains almost as big as early Homo sapiens. They were also expert hunters known to use handaxes and wooden thrusting spears. Evidence for these tools were found in Germany(Schoningen, Lehringen) and UK(Clacton).
The next three species that I will mention lived roamed the earth with Homo sapiens. We interacted with them, formed friendships, mated them, learnt from them, and fought them to extinction.
Homo floresiensis
AGE: 700,000–12,000 yo
LOCALITY: Flores, Indonesia
FOSSIL RECORD: One complete skull, parts of 11 individuals
They evolved separately on the Flores island of Indonesia. This was the last species to go extinct about 12,000 years ago. The caves where floresiensis fossils were found show evidence of use by modern humans over last 10,000 years.
This was a very small hominin about 3 ft tall. The island of Flores has long been separated from Australia and Asia. Its isolation could, over a long period of time, have lead to hominin species living here shrinking in size when compared to their mainland relatives — a phenomenon known as island dwarfism.
Homo neanderthalensis
AGE: 430,000–30,000 yo
LOCALITY: across Europe and southwest Asia
FOSSIL RECORD: a number of entire skeletons and various fragments from more than 275 individuals
Named after the Neander Valley near Dusseldorf, Germany where the human like bones along with worked stone tools and bones of extinct Ice Age animals such as mammoths, giant deer and woolly rhinos were discovered in 1856. As you can imagine this discovery would have caused quite a stir back then as it depicted our ancestry completely different from the biblical version. Not only we had extinct cousins, the antiquity of humans was now far greater than 2,000 years.
Neanderthals thrived in Europe for around 300,000 years before modern day humans arrived there. They occupied much of Europe from Wales south to Gibraltar and eastwards to Caucasus.
Them along with the longest surviving Homo erectus were the most successful species of its time. The record of neanderthal life is remarkable because it includes individuals of all ages, from premature fetuses to the very elderly. Remains of more than 100 fetuses and small children have been found hinting at high mortality.
They survived the dramatically fluctuating climate changes of the final part of Quaternary Ice Age until around 28,000 years ago when they became extinct.
MODERN BEHAVIOR: In many ways, neanderthals were just like modern humans. In fact, at their time they were more advanced than the coexisting Homo sapiens. Neanderthals have shown evidence of cooking their food by boiling it. They built even more sophisticated tools than Homo ergaster’s handaxes. Some of these tools used ancient adhesives. They hunted birds for feathers and exploited aquatic resources. Neanderthals also used to bury the dead. Fossilized finds in Kebara cave, Israel hint towards deliberate burial. Neanderthals also had modern traits such as planning ahead, complex social networking, technological innovation, flexibility to adapt to changing environments, symbolism, and rituals. They also consumed plants with medicinal properties including penicillin fungus. Fossils in St. Cesaire, France have shown evidence of neanderthals using items of personal adornment. There is also evidence of them using makeup found in shells holding dyes.
Homo denisovan
The extraction of DNA from a 41,000 yo finger bone and teeth from Denisova cave in Siberia have led to the discovery of a completely new species. These Denisovans migrated out of Africa separately from Neanderthals and Homo sapiens. In the evolutionary tree they branched of from us and Neanderthals about a million years ago. Denisovans interbred with modern humans. Traces of denisovan DNA is found in modern day humans.
Homo sapiens and the Story Beyond
Homo heildelbergensis that remained in Africa most likely gave rise to the first Homo sapien about 200,000 years ago. Not much happened for next 130,000 years. We remained in Africa and didn’t evolve all that much. Our cousin neanderthals were way more advanced than us. But something happened about 70,000 years ago. These archaic humans migrated out of Africa and took over the entire Earth causing all other hominin and many other animals species to go extinct. The story of how this may have happened is explained in Yuval Noah Harari’s Sapiens. I highly recommend this book to anyone interested in the story of our orginins, but be warned, it’s not pretty. It’s full of inconsideration and brutality on our part, most likely a gift to us by our more aggressive chimpanzee ancestors. I will summarize the story of how we went from a nobody species to the master species.
Yuval Noah Harari breaks down our rise as modern intelligent humans in three distinct revolutions:
COGNITIVE REVOLUTION: Exactly what happened 70,000 years ago that made Homo sapiens so adept to rule is debatable. But the most leading theory is an accidental genetic mutation. This mutation changed the inner wiring of our brains and gave rise to a huge congnitive revolution by giving us the gift of language. With language, we could form big supportive communities and make complex plans. Within a remarkable short period, sapiens reached Europe and Asia. Between 70,000–30,000 years ago sapiens invented boats, oil lamps, bows and arrows, needles for sewing.
AGRICULTURAL REVOLUTION: Until 12,000 years ago, humans foraged and lived as hunters and gatherers. Then 12,000 years ago, someone figured out how to plant things. This was much easier than foraging as a small area of land could now provide for a larger population. This revolution caused human population to grow and spread exponentially. Keeping track of harvests also led to development of maths and record keeping.
SCIENTIFIC REVOLUTION: Rise of agricultural revolution freed up many people to think and share knowledge. Writing was invented. And before you know we have Indians building wheels and Egyptians building pyramids. And now we have humans discovering the inner workings of the very universe that birthed us.
This entire growth of modern day humans happened extremely fast. Humans climbed from the bottom of food chain to the very top in an instant compared to evolutionary times. We went from feeding on bone marrow from leftover bones to feeding on entire animals. This exponential climb to the top of the food chain was disastrous in many ways as no species was ready for it, including us. This is what resulted in human traits such as anxiety, fear, and mistrust as we were used to always being on edge due to predators. And it led to extinction of 70% of the species that existed with us as we continued to burn forests for farming and killing animals for food and clothing.
But here we are today, the only living hominin species. It cost a lot to get to this level and now we face a dire responsibility towards not only our fellow animals companions but also towards our planet.
Hope you found this post informative as well as interesting.
