What makes something a hominin

It consists of nested, hierarchical groups that get more and more narrow as you go down the taxonomic chain. Phylum: Chordata animals that have a notochord at some point in their lives; in fish, reptiles, birds and mammals, the notochord becomes the vertebral column. Family: Hominidae modern humans and our close extinct relatives, such as Ardipithecus and Australopithecus. Under this system, the term hominid refers to members of the Hominidae family in taxonomy, names that end in -idae refer to a family.

For the first time, hominin brain size exceeded that of other apes. At this point, Homo erectus appeared. They made sophisticated tools , such as stone handaxes. This was a major technological advance. Handaxes needed skill and planning to create, and you probably had to be taught how to make one. It may have been a meta-tool — used to fashion other tools , such as spears and digging sticks. Like us, Homo erectus had small teeth. That suggests a shift from plant-based diets to eating more meat, probably from hunting.

The big-brained Erectus soon gave rise to even larger-brained species. These highly intelligent hominins spread through Africa and Eurasia, evolving into Neanderthals , Denisovans , Homo rhodesiensis and archaic Homo sapiens. Technology became far more advanced - stone-tipped spears and firemaking appeared.

Objects with no clear functionality, such as jewellery and art , also showed up over the past half-million years. Some of these species were startlingly like us in their skeletons, and their DNA. They might have thought of themselves, even spoke of themselves, as human.

The Neanderthal archaeological record records uniquely human behaviour , suggesting a mind resembling ours. Neanderthals were skilled, versatile hunters , exploiting everything from rabbits to rhinoceroses and woolly mammoths. They made sophisticated tools, such as throwing spears tipped with stone points. They fashioned jewellery from shells , animal teeth and eagle talons , and made cave art.

And Neanderthal ears were, like ours, adapted to hear the subtleties of speech. We know they buried their dead , and probably mourned them. To the extent Neanderthals were like us, they must have been capable of acts of great kindness and empathy, but also cruelty, violence and deceit. I admit this sounds speculative, but for one detail.

We met them, and we had children together. That says a lot about how human they were. But for Neanderthal genes to enter our populations, we had to not only mate but successfully raise children, who grew up to raise children of their own.

Mixing of genes also required their hybrid descendants to become accepted into their groups — to be treated as fully human. We were probably responsible for the extinction of these species. But there must have been times we looked past our differences to find a shared humanity. Extinction of Neanderthals, Denisovans, and other species took hundreds of thousands of years.

Why, if they were so like us, did we replace them? However, if you compare the humerus and femur and the muscles that cross the respective joints deltoids and gluteal muscles, respectively , you will definitely see similarities. Our pelvis is very unique and interesting. It has changed significantly from an ape pelvis see Figure 5.

The pelvis is made up of three bones: the two lateral bones, termed innominates or os coxae, and the sacrum. Collectively, they form a basin-like structure that holds our internal organs while providing support for our upper bodies. Each innominate consists of three bones that fuse during development: the ilium , ischium , and pubis see Figure 5. They meet at the hip joint.

Hominin innominates became shorter and broader, so that the ilium wraps around laterally from an earlier, more posterior position. This changed the orientation and action of our hip muscles, allowing for our striding gait and the ability to balance our weight on one fully extended leg while the other leg is in the swing phase. A portion of the gluteus maximus muscle inserts behind the hip joint in hominins versus lateral in chimps , and thus instead of abducting the femur moving it out laterally, as when doing jumping jacks , it changed to a powerful hip extensor backward motion for running.

Figures 5. The iliac crest is long and curved, as the bone wraps around laterally. The iliac blade is short but expanded horizontally. The iliac blades are buttressed or reinforced to handle the stress of our upper body weight.

The thick section of bone, termed the iliac pillar , can be seen running from the iliac crest at the iliac tubercle down behind the hip joint. The articular area, termed the acetabulum , is large and deep, providing a stable socket for the ball-like head of the femur.

The joints of the pelvis are very strong and relatively immobile compared to the shoulder joint. The sacroiliac joint between the ilium and the sacrum is large and more posterior and proximal to the hip joint than in quadrupedal apes.

Together with the strong pubic symphysis anterior joint where the pubis portions of the two innominates meet , these characteristics make for a very stable supporting structure.

The lower limb consists of the femur of the thigh, the tibia and fibula of the leg, seven tarsal bones of the ankle, five metatarsals of the body of the foot, and phalanges of the digits three per toe and two per big toe or hallux. The head proximal ball-like structure of the hominin femur is large. The femur angles medially inward from hip to knee, so that our upper body weight is transferred down through our hip joints to our knees.

This is termed the carrying or bicondylar angle. The knees of quadrupedal apes are directly below the hip joint, so there is more strain on the knee joints when they walk bipedally see Figure 5. We have two bulbous structures on the bottom of each femur, termed condyles. The innermost condyle, the medial condyle , has lengthened in hominins so that the femur sits on top of the flat tibial surface. If this were not the case, the medial condyle would not make contact with the tibial plateau , due to the bicondylar angle.

Weight is transferred through our innominate, hip joint, and lateral condyle of the femur see Figure 5. Each gluteus medius muscle alternately supports the opposite side of the torso and pelvis, so that it does not slump on the unsupported side.

Our feet see Figure 5. The tarsal bones of the human ankle are large and robust for support. The joint between the distal tibia and fibula is fairly immobile, so that the two bones are firmly lashed together. Together, they articulate with the talus most superior tarsal bone in a hinge joint. We have lost much of the mobility of an ape foot and thus have become less agile in climbing over time. The calcaneus or heel bone is very large and robust and, along with the ball of the foot distal end of the first metatarsal and the area below the baby toe fifth metatarsophalangeal joint , forms a tripod structure.

Our feet have three arches for support, shock absorption, and forward propulsion; they are the medial and lateral longitudinal arches and the transverse arch. Hominin toes became shorter and less curved over time. While shorter, the hallux became more robust and lost its degree of divergence and opposability, by coming into alignment with the lateral four toes, i. Just as there are evolutionary trends that characterize primates, there are also trends that characterize the hominins, i.

While all of the morphological changes involved with bipedalism are hominin trends, there are also relevant characteristics in other parts of the body. Most notable, our ancestors and their relatives became increasingly more intelligent.

This likely occurred in response to environmental stresses as well as competition with other hominins for resources. Skull size and shape changed in response to encephalization , i. Brains are very costly organs and researchers believe that in order for brain size to have increased, there would have had to have been a corresponding decrease in some other costly organ system. It is hypothesized that a higher quality diet allowed the hominin gut to shrink and, in turn, the brain to expand.

Marked encephalization in the hominin lineage began with the first members of our own genus: Homo. While there is some evidence that earlier species e. While the dimensions of the thorax remained wide and shallow, the shape of the rib cage changed from a more conical, ape-like thorax that could accommodate a large gut, to our more barrel shape.

As our brains became bigger, our ancestors gave birth to increasingly altricial helpless young that continued their development outside of the womb. Our offspring require protection and care for a much longer period than those of the other great apes, i. It is possible that they also did some hunting of small animals in much the same inefficient manner of chimpanzees today.

They probably ate insects and eggs as well. The classification of Australopithecus garhi is still very problematical. This Ethiopian fossil has been dated to 2. Largely for that reason, some paleoanthropologists have suggested that garhi is a variant of africanus. However, several features of the head of garhi look more like a holdover from the older afarensis species.

On the other hand, the relative lengths of the arms and legs of garhi are more reminiscent of the first humans. The discovery of butchered animal bones with garhi suggests that their diet included at least some meat, as was the case with africanus.

Paranthropoid Species. T he australopithecines have been referred to collectively as gracile species literally "gracefully slender" of early hominins. Most of them were relatively small, slender, and delicate boned compared to the somewhat more muscular, robust species paranthropoids that mostly came later. However, this is not always a reliable descriptive distinction because the range of variation in physical appearance of the two groups of species overlaps.

Subsequently, some individual graciles were bigger than some of the robust ones. However, the robust species shared some characteristics of their heads that dramatically show that they had diverged from the evolutionary line that would become humans.

They had larger faces and jaws accompanied by pronounced sagittal crests in the case of males. They also had much larger back teeth premolars and molars and smaller front ones incisors compared to gracile australopithecines and early humans who were alive at the same time.

Australopithecus gracile body Paranthropus robust body Paranthropus teeth upper human teeth lower Little is known about Paranthropus a ethiopicus the "black skull" other than it apparently was one of the earliest robust species--it lived about 2. So far, this species has been found only in East Africa. Since it had a smaller brain than the other robust species and it was early, aethiopicus is thought to be a transitional form from one of the gracile species that came before.

It had an unusually large sagittal crest shown below. Paranthropus robustus was a South African robust species that lived about 2. They had strong jaws and very large molar and premolar teeth with thick enamel. Males also had pronounced sagittal crests, though not as large as the species listed next.

Paranthropus boisei was a super-robust East African species that lived about 2. They tended to be more massive and beefy-looking even than Paranthropus robustus.

Male boisei were especially muscular. Like their South African cousins, robustus , they had prominent sagittal crests and very large grinding teeth with thick enamel.

These teeth would have been capable of cracking hard nuts and dry seeds. However, such food items may not have been important in their diet. Microscopic analysis of dental wear patterns and carbon isotope analysis of teeth indicate that what boisei predominantly ate was soft foods such as grasses, leaves, roots, and possibly even meat.

Early Hominin Body Size. The early hominins were significantly smaller on average than modern humans. Adult male australopithecines were usually only about 4. Females were much smaller and less muscular. They were usually 3. This is greater sexual dimorphism than is found in human populations today. In some australopithecine species, sexual dimorphism may have been nearly as great as among the great apes.

Possible Evolutionary Links. There has been a gap in the fossil hominin record for the crucial period before 4. New discoveries are now beginning to fill in the missing picture of evolution leading to the australopithecines at that early time. Beginning in , Tim White and several of his Ethiopian colleagues found fossils of what may be the immediate ancestor of the australopithecines at the Aramis site in the Middle Awash region of Northern Ethiopia.

The teeth of these very early fossils seem to have been transitional between apes and Australopithecus anamensis. Among the living apes, they were most similar to chimpanzees, however, they were not apes as we usually think of them today.

These Aramis fossils date to about 4. Because of their primitiveness, White has given them a new genus and species designation Ardipithecus ramidus , nicknamed "Ardi" rather than include them with australopithecines.