Arxiu d'etiquetes: hominans

Ancestors they didn’t teach you in school

Surely you know any of the following names because they are classic ancestors we learned in school: Lucy, Homo habilis, Homo erectus, Neanderthals… but our history has many more players, and every so often new discoveries are made that change our lineage tree. Find out in this article the latest findings your teachers could not explain to you .

HOMO NALEDI

Reconstrucción facial de Homo naledi por John Gurche. Foto de Mark Thiessen.
Homo naledi’s facial reconstruction by John Gurche. Photo: Mark Thiessen.

It is almost forced to start with one of the latest discoveries that is encouraging discussions in paleoanthropology to gain a key position in our family tree. The discovery of a new species, Homo naledi, was published the September 10, 2015 by Lee Berger et al. It was discovered in a cave system in South Africa named Rising Star at the Dinaledi chamber (“Naledi” means “star” in the local language, Sesotho). It is especially interesting for several reasons:

  • At the moment in the site have been found more than 1,700 human fossils accumulated, making it the largest of South Africa, behind the famous Sima de los Huesos (“Pit of Bones”, Atapuerca, Spain), the largest of the world, with more than 6,000 fossils.
  • The cave is very difficult to access, with corridors of only 19 cm wide, so it was a selected team of 6 thin paleoantropologysts (all women) that reached them.

Esquema del sistema de cuevas de la cámara Dinaledi. Imagen de Jason Treat, NGM Staff, NGM maps, fuente: Lee Berger, Wits. Tomada de National Geographic.
Scheme of the cave system of Dinaledi’s chamber. Image by  Jason Treat, NGM Staff, NGM maps, Source: Lee Berger, Wits. Adapted from National Geographic.

  • The bones belonged to 15 individuals of all ages, male and female, so we can get extensive information about the new species. Some were even on the floor of the cave without mineralize.
  • The physical characteristics of H. naledi are a mix of Homo traits (height, feet) and Australopithecus (shoulders, chest, pelvis), the genus from which most scientists believe Homo appears about 2.8 to 2, 5 million years ago. This may suggest that H. naledi could be the first Homo, the missing link between Australopithecus and us.

    Una parte de la impresionante cantidad de huesos de Homo naledi descubiertos. Foto de John Hawks
    Some of the impressive number of bones discovered Homo naledi. Photo by John Hawks
  • The most intriguing of this discovery, it is believed that the bones were placed there deliberately. By geography, access to the cave was the same as today, they could not fall into the pit, the bones could not be brought by a water flooding or any animal, they have no marks of violence … It could be a funeral ritual? So far, the first rites are attributed to H. neanderthalensis, with most modern physical characteristics and a large cranial capacity compared to H. naledi (1.475 cm3 versus 560 cm3  at the most).

The oldest known Homo fossil, 2.8 million years old, corresponds to a jaw found in Afar in March 2015 which has not been associated to any species. Was H. naledi the first Homo? Is it really an ancient species? Is it possible they had self-awareness so early and cared for their dead? Unfortunately, researchers have not been able to date the remains yet, so many questions remain unanswered and we will must wait for future interpretations of one of the most important discoveries of recent times.

THE DENISOVANS

In Denisova Cave (Siberia) in 2008 was found a non-spectacular fossil: a piece of a finger bone that was dated 30,000 years old and attributed to an individual of about 8 years which turned out to be a gir. But when DNA was extracted, it was concluded that belonged neither to H. sapiens or H. neanderthalensis, but to a new species. Later two teeth of another individual of the same population were found. In the same cave also Sapiens and Neanderthal remains were found.

Diente, muela, denisova, denisovanos, teeth, tooth, denisova
The denisovan teeth.  Photo by Max Planck Institute.

Is it possible that Denisovans hybridized with Sapiens? DNA studies in the current populations indicate that 5% of DNA aboriginal Australians, Papuans and other peoples of Melanesia is Denisovan. On the other hand we know that 20% of the DNA of accumulated European populations is Neanderthal.

WHERE DO WE LOCATE THEM IN OUR FAMILY TREE?

It is thought that Neanderthals and Denisovans had a common ancestor (H. heidelbergensis), who emigrated to western Europe and Central Asia evolving to H. neanderthalensis, who subsequently hybridized with us, and from Southeast Asia where would evolve in the hominin Denisova, who also hybridized with H. sapiens. This would explain the presence of DNA in the current populations of Australasia.

HOW THEY WERE LIKE?

The absence of more fossils or traces of objects and tools prevent us to know how they looked like and what were their skills. Nor it has been found explanation for the lack of Denisovan DNA in the Russian or Chinese populations, so close geographically to the Denisova cave. Denisovans remain a mystery to science.

THE FLORES WOMAN

Homo floresiensis. Reconstrucción de John Gurche
Homo floresiensis. Reconstruction by John Gurche. Photo by Chip Clark

Homo floresiensis, as its name indicates, lived on the island of Flores (Indonesia) only between 95,000 and 12,000 years ago. It was discovered 12 years ago. It is the only site where this species is found.

As in previous fossils, the mix of features caught the attention of the scientific community, especially for its small cranial capacity and height, earning them the nickname hobbit. First they thought it was an individual with a pathology, or a pygmy of a known species, as their morphology was very strange in a so modern fossil. But now we have remains of at least 12 individuals with the same traits, so we can talk (for the moment) of another species.

HOW THEY WERE LIKE?

  • Small height: the most complete skeleton belongs to a female only one meter tall and 25 kg weight.
  • Small skull: their cranial capacity (380-420 cm3) was similar to the current Australopithecus or a current chimpanzee, but the brain had a more similar Homo anatomy. The teeth were large relative to the skull.

Reproducción de cráneo de Homo floresiensis. American Museum of National History. Foto de Mireia Querol
homo floresiensis (LB1) skull cast. American Museum of National History. Photo by Mireia Querol

  • Long feet and short legs: feet were very long in relation to the legs, which were short and stout. This and more features suggest that locomotion was different from ours and were bad runners.
  • Long arms: besides a proportion nearest to Australopithecus and H. habilis than H. sapiens, arms were robust and had a powerful musculature.
  • Stone tools and fire: besides the existence of tools of earlier hominans found in the cave, some tools have been associated to H. floresiensis with a technology similar to the Oldowan Industry, the first to be invented. Also they dominated the fire.

WHY THEY WERE SO SMALL?

Controversy continues: was a direct descendant of Australopithecus (how could they have traveled so far from Africa?), or a recent member of our family tree so small due to lack of resources?

The insular dwarfism is an evolutionary process due to a long-term isolation in a small area with limited resources and lack of predators. Flores pygmy elephants (Stegodon) hunted by H. floresiensis  with this adaptation were also found. The opposite process it is the island gigantism, in which animals that are usually small on the continent are giants in the islands, such as the Galapagos turtles and the extinct lizards or rats of Flores.

Un lagarto gigante se enfrenta al hombre de Flores. Imagen de National Geographic
A giant lizard faces Flores man who has caught a rat. Image by National Geographic

H. floresiensis may be the result of this dwarfism, and some scientists believe it could actually be a reduced Homo erectus. The majority opinion today is that they were already so small when they reached Flores (such as the  Australopithecus from whom evolved), and modern features are due to convergent evolution with H. sapiens. Unfortunately it has not been able to extract DNA in good condition to put them in the phylogenetic tree for sure.

How did they get to Flores? They had a language, art and cultural expressions? Did they get in contact with our species? They were extinct due to a volcanic eruption? Who made the other ancient tools previous to H. floresiensis? The debate and the unknowns remain open.

REFERENCES

 

Hands-free in the Pliocene

In the previous post we discovered the anatomical changes associated with bipedalism in early hominids and the relationship of the selection of this feature with climate change. Is bipedalism a trait that makes us human? What are the advantages over other quadruped animals?

WHAT IS THE PLIOCENE?

Since the origin of our planet, geologists have divided time into different divisions of millions of years: the eons (Archean, Proterozoic and Phanerozoic), which in turn are divided into different eras. The Phanerozoic (from 542 Ma to present) is divided into three eras, from oldest to newest: Paleozoic, Mesozoic and Cenozoic. In this link you can see  the major biological milestones for each epoch.

cenozoic
Cenozoic detail. Full image

The Miocene is the time when the hominoids appear, (Proconsul is the most famous genus) and in the Pliocene appears, among others, Australopithecus. Homo sapiens do not appear until the Holocene, a blink in the planet’s history, as they say.

Usually the climate changes that have been happening throughout the history of Earth, represent extinction, diversification and new species, and so does our evolutionary branch: many authors relate climatic fluctuations with milestones of hominins. If you are interested in this interactive you can investigate this issue.

slideshow_plate_tectonics_02
Position of the continents in the Miocene after the collision between the Eurasian and Indica plates. (Photo by The Burgess Shale)

One of these climatic changes (caused by the collision of the Eurasian and Indica tectonic plates,  giving rise to the Himalayas and changing wind currents) was responsible for the disappearance of large tracts of rainforest, giving way to a landscape shrub or savanna. Hominoids who stayed in the forest, led to the current nonhuman apes, while those who occupied the savannatrees mosaic led to hominins, our lineage. What are the advantatges of bipedalism in that landscape?

ADVANTATGES OF BIPEDALISM

  • Handsfree: the two free limbs can be used to transport food and offspring. You can reach fruit trees without stepping on them and later, will allow the manipulation of tools, hunting and cultural events.
  • Less heat: without offering the entire back surface to the sun, and separating the body from the hot ground, it allows cope better with high temperatures and survive with less water.
  • More energy: walking on two legs consumes less energy than walking on four. This allow walking longer distances with less food, which is important in an environment where you have to flee or find food constantly. We have a great strength to walk or run many kilometers compared with quadrupeds.
  • Best visual field: the eyes have a higher position and can detect potential predators over shrubs or drive them away with stones if necessary. It is also easier to spot food sources.
  • Intimidating appearance: upright posture appears to increase body size and can avoid confrontations with certain predators.
  • Better communication: the insertion of the skull with the spine, leaving enough space for the vocal cords allow, over time, the appearance of articulate speech. Although other apes had the same brain capacity to talk, morphologically it is impossible because of the structure of their vocal apparatus.
Algunas ventajas del bipedismo. (Ilustración de Karen Carr Studios)
Some advantatges of bipedalism. (Illustration by Karen Carr Studios)

DISADVANTAGES OF BIPEDALISM

  • Low speed: for short distances, running on two legs is slower than four, in case of an unexpected attack by a predator, the chance to escape decreases.
  • Back pain: the stress that suffers our spine and legs throughout life due to upright posture, is the most likely cause of back pain, knees, hips and feet that suffer a large part of the world population.
  • Birth complications: our birth canal is narrower due to the structure of our pelvis, plus the large size of the skull of the young, it causes more pain and complications in human births compared to other mammalian quadrupeds.
Canal del parto en una mujer (izquierda) y una chimpancé (derecha). Foto tomada de Jose Mª Bermúdez de Castro
Birth canal in a woman (left) and a chimpanzee (right). (Photo taken of Jose Mª Bermúdez de Castro)

Thus, despite the disadvantages, in a warm environment, rather arid and with few trees for shelter from predators, who survived were bipedal hominoids. We consider our bipedalism as a trait that makes us human, as it is unique among animals: only birds are fully bipedal -like some extinguished dinosaurs, and except the penguin -with clumsy gait, their spine is not perpendicular to the ground, like ours.

REFERENCES

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Who are the hominids?

Today’s article is dedicated to primates. We will talk about some of its key features, the classification of the living species and we will discover who the hominids and hominans are.

GENERAL CHARACTERISTICS OF PRIMATES

Primates are an order of placental mammals that appeared about 65 million years ago in the tropical rainforest. There are currently over 400 living species, most of them arboreal. Since there are no single trait that defines them, they are difficult to classify; so we have to consider a set of features, which are:

  • Complex visual system: with frontally placed eyes, their vision is stereoscopic, allowing them to perceive the distance and depth with great accuracy. Most species can see in color.
  • High mobility of the shoulder: allows an easy arm movement in all directions. Hands and feet have five fingers and opposable thumb (at least in hands) allowing them to grasp and manipulate objects with precision. Although some have claws, most have flat nails and all (except some orangutans) have a flat nail on the big toe.
  • Torso and tail: several primates rest and move with an erect torso. Except apes, in some cases they have a prehensile tail, and can use it as a fifth limb.
  • Brain size: besides some species of toothed whales, some primates have, in relation to the body, the largest brain of all mammals.
  • Social organization: only orangutans, some lemurs and galagos are solitary, other primates are organized in complex social groups.

Gorila comiendo (Gorilla sp.) donde se aprecian algunas de las características descritas (Foto: pixabay.com)
Gorilla eating (Gorilla sp.) where whe can see some of the characteristics. Photo: pixabay.com

 

CLASSIFICATION

The relationships among the different groups of primates were not clearly understood until relatively recently, so the commonly used terms are somewhat confused (mokeys, apes…). Modern cladistic classifies primates in two suborders, Haplorrhini (“dry-nosed primates”) and Strepsirhini (“wet-nosed primates“). A possible classification would be:

Taxonomia primates english
Primates taxonomy. Clic to enlarge. Created by Mireia Querol based in an image taken of humanorigins.si.edu.

Traditionally primates are classified into three groups: prosimians, monkeys and apes.

PROSIMIANS

Prosimians are the oldest primate group. They are distributed throughout Southeast Asia and Africa marginal islands. Prosimians include lemurs, lorises, galagosindris, the aye-aye and tarsiers. They share the following characteristics:

  • Claws instead of nails (they have at least a fingernail)
  • Long snout with wet nose. They have the best sense of smell among primates
  • More lateral orientation of the eyes than other primates. These are big and have good nocturnal vision
  • Mobile pinna
  • Minor brain proportion than other primates

Aye-aye (Daubentonia madagascariensis). (Foto: Frans Lanting)
Aye-aye (Daubentonia madagascariensis). Photo: Frans Lanting

 

Tarser de Filipines (Foto: Kok Leng Yeo)
Philippines tarsier (Carlito syrichta). (Photo: Kok Leng Yeo)

OLD AND NEW WORLD MONKEYS

The New World monkeys are distributed throughout Central and South America. They have a long, often prehensile tail. The muzzle is flat and the nostrils are situated in the side. They are completely arboreal. The best known representatives are marmosets, spider monkeys, capuchins, and sakis.

Sakí cariblanco macho (Pithecia pithecia). (Foto: Charles Miller).
Male of White-faced saki (Pithecia pithecia). Photo: Charles Miller

 

The Old World monkeys are distributed throughout Africa and Asia. Usually they are bigger than New World monkeys. The nostrils are directed downward or forward. The Old World monkeys cover a wide range of species, such as macaques, baboons, mandrills, mangabeis, drills, colobus, proboscis monkeys, langurs

Langur dorado (Trachypithecus geei). (Foto: Wikimedia).
Gee’s golden langur (Trachypithecus geei). Photo: Wikimedia

 

APES

Apes are divided into two families: Hylobatidae (gibbons and siamangs) and Hominidae (orangutans, gorillas, chimpanzees and humans). They are distributed throughout West and Central Africa and South and Southeast Asia, except humans: we are distributed all over the planet and habitats. Apes have a flat face, with the nostrils downwards and an anatomy that facilitates upright posture and materials handling, including the creation and use of tools in some species.

Bonobo (Pan paniscus). (Foto: Pierre Fidenci)
Bonobo (Pan paniscus). Photo: Pierre Fidenci

In conclusion, hominids are human beings (Homo sapiens) together with orangutans (two species: Pongo pymaeus and Pongo abelii), chimpanzees (Pan troglodytes), bonobos (Pan paniscusand gorillas (two species: Gorilla gorilla y Gorilla beringei), because we all belong to the family Hominidae. The term also refers to all fossil species of this family, and therefore our ancestors, that we will discuss in future articles on human evolution. However, to refer exclusively to our evolutionary branch (including H. sapiens) the used term is hominans or hominas, which refers to a tribe (Hominini) of the Hominidae family.

REFERENCES

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