Human evolution


Steinham Man is represented by a complete skull found in 1933 from a gravel pit at Steinham site in Germany. Its age is estimated to be same as for Swanscombe man, from the second interglacial period. Cranial capacity was 1070 to 1175 cc. Fore head was high but eyebrow ridges were heavy and the nasal opening broad as in Neanderthals.

Ehringsdorf Man is also known from Germany with a cranial capacity of 1350 cc. It lived up to 120,000 years ago. Forehead was well developed, eyebrow ridges heavy and chin reduced.

Swanscombe Man is known by two pieces of the skull roof consisting of one occipital and two parietal bones that are unusually thick. Skull is broad at the back but the occipital region is not projected behind as in Neanderthals. Cranial capacity was 1300 cc. Some stone tools were also discovered from the same site.

Fontechivade Man fossils are from France. Skull bones were thick and cranial capacity about 1400 cc. Supraorbital ridges were not prominent.

Solo Man is known by partial skull and 2 femur bones discovered from Solo river in Java in 1933. Forehead was low and eyebrow ridges heavy. Cranial capacity was 1300 cc.

Rhodesian man was discovered in Rhodesia (= Zimbabwe) in 1921. Cranial capacity was 1300 cc. Eyebrow ridges were heavy and jaw was projecting forward, although the dental arch was parabolic. The Rhodesian man was about 6 feet tall, neanderthaloid in appearance and is now regarded as a subspecies of Homo sapiens.

Neanderthal Man (Homo neanderthalensis) is known originally from Neander Valley in Germany. Later, fossils of about 200 individuals were unearthed from 70 sites in Austria, China, France, England, Germany, Greece, Italy, Iraq, Israel, Java, Russia and Yugoslavia.

The species lived between 200,000 and 30,000 years ago. The average cranial capacity was 1450 cc, which is greater than in modern man, but the brain was large posteriorly and ventrally. They were stout and powerfully built people, weighing over 80 kg and having an average height of 5’6”. Long bones were thick, slightly curved and had large areas for muscle attachment. Forehead was low and slanting, eyebrow ridges were heavy and cheek bones were large. Nose was broad and chin was absent. Stature was robust and completely upright. Teeth were large.

They were cave dwellers living in the most adverse environmental conditions and used fire, made stone tools and crude carvings and practiced burial. There is strong evidence of ritualistic practices, religious beliefs and ceremonious burials. The classic Neanderthals come from fourth interglacial period in Europe and had stocky and rugged stature, broad nose, stout mandible, projecting occipital region and no chin.

Causes of extinction of Neanderthals are not clear. The most plausible explanation is that a more advanced species, Cro-Magnon man evolved in Africa and migrated to Europe about 40,000 year ago and exterminated the Neanderthals. However, recent findings indicate that extinction of Neanderthals was not so fast and that it coexisted with Cro-Magnon for about 10,000 years and perhaps produced viable hybrids.

That leads to another possibility that they must have interbred with the new and more advanced populations immigrating from Africa, producing the modern man. But a study of mitochondrial DNA sequences recovered from the skeleton of a Neanderthal suggests that modern humans are closely related to each other than to Neanderthals.

Cro-Magnon Man(Homo sapiens fossilis) was a contemporary of Neanderthal man and lived in Europe during the upper Paleolithic period (about 40,000-10,000 years ago). Large number of fossils was found from a cave in Cro-Magnon in France. Male was 6 feet and female 5 feet 6 inches tall. Skull was like modern man, with a distinct chin, flat eyebrow ridges and orthognathous face. Teeth and jaw were distinctly like modern man. Cranial capacity was about 1500 cc., same as that of modern man.

They showed technological advancement in using bones, antlers, stones etc. to make tools and spears and also specialized tools such as needles, harpoons, engraving tools, blades, soft hammers and heat-treated flints. They used ornaments for the first time and performed rituals. Coloured pictures of animals in the deepest parts of the caves and also carvings of wood, ivory and stones point to their advanced skills. They apparently knew the use of fire but did not practice agriculture or domestication of animals. They also buried their dead with some rituals. 

 Both Cro-Magnon and Neanderthal man lived during the glacial period, when their main occupation was hunting wild animals for food, which they cooked on fire in caves. Cro-Magnon had better intelligence and advanced tools and arms and hence perhaps exterminated Neanderthal.

Towards the end of glaciations, they probably migrated to warmer parts of the world and settled down in colonies along the rivers to practice agriculture and domestication of animals, which gave them sure and constant supply of food. Evolution of man after that was very fast as compared to the earlier slow pace of evolution during Pleistocene epoch.

Homo floresiensis. Also named as Homo hobbit, the discovery of the little man from limestone cave at Liang Bua on the Indonesian island of Flores by the Australian archaeologists surprised everyone. The 18,000 year old fossils were only a meter tall and had cranial capacity of only 380 cc. These tiny people lived in isolation in the far-flung Indonesian island where giant rats, tiny elephants, Komodo dragons and other large lizards were abundant. The isolation forced the species to remain small-sized and live in holes in the ground to escape giant predatory lizards and hunt giant rats for food.

The molecular evidence.  Mitochondrial DNA is inherited maternally through the cytoplasm of the egg which contains about 100,000 mitochondria (sperm contains insignificant amount of mtDNA, only about 50), and is not subjected to the same selection pressure as the nuclear DNA.

The rate of mutation in mtDNA is ten times faster than nuclear DNA and is constant and hence can be measured to reveal a relationship between two species that emerged from common ancestor. Cann et al. (1987) analyzed 144 mtDNA samples from human groups of different origin and estimated the age of common ancestor as 150,000-290,000 years. Linda Vigilant et al. (1991) studied mitochondrial DNA of 189 people from different regions. Their direct maternal ancestry was found to converge to a single female in Africa called “mitochondrial Eve” that lived between 1,66,000 and 2,49,000 years ago.

  Data on amino acid residues indicates that chimpanzee and gorilla are genealogically closer to man than to other apes. The fusion of acrocentric chromosomes, which is called Robertsonian translocation, has perhaps taken place, which reduced the number of chromosomes from 48 in apes to 46 in man. Such chromosomal rearrangements and also pericentric and paracentric inversions alter the metabolic pathways and thus produce reproductive isolation. 

Single origin versus multiple origin of man

Molecular evidence seems to support the African origin of humans and then their migration to other continents to develop racial differences. All non-African mitochondrial DNA sequences are only variants of the African sequence, and African populations possess the maximum mtDNA variability suggesting their ancient character. A study by Hammer and co-workers of Y-chromosome of more than 1500 individuals from all continents also points to the African origin of man. Human populations all over the world are basically similar in anatomy and genetic composition and hence must have had a single origin in Africa.

Multiple origin hypothesis or multiregional proposal, on the other hand, suggests that all human populations in different continents evolved in parallel over long periods from Homo erectus. Hominids migrated out of Africa much earlier than the subsequent origin of modern man about 100,000 years ago in different geographic regions of the world. Fossils from the Chinese and Australian regions show continuous and independent progression from the Homo erectus stage to the present. Human ancestors were highly mobile creatures and hence constantly exchanged genes between populations to break the reproductive isolation and keep genetic variability to the minimum.

Cultural and social evolution of man

Modern humans, being highly social, learn from their experiences, share these experiences with the others and modify their behaviour based on constant learning. Unlike other animals, they are also capable of modifying their environment to suit their needs and keep considerable control over it.

An important difference between the genetic exchanges and cultural exchanges is that the former can take place between parents and offspring while the latter can take place among the unrelated individuals. Therefore, while the biological traits are transmitted vertically within the lineages, cultural traits are transmitted both vertically and horizontally within lineages or among the unrelated individuals.

Cultural evolution is therefore much faster than the genetic evolution. While the cultural evolution follows Lamarckian mode of inheritance, the biological evolution is driven by natural selection in which information is transmitted through DNA and the mechanisms of heredity. Cultural evolution is independent of genetic system and can take place without making any change in the genes.

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