Life in the Universe: II. Origin and History of Life on Earth part-3 - Remote Sensing Application - Completely Remote Sensing, GPS, and GPS Tutorial
Life in the Universe: II. Origin and History of Life on Earth part-3

To most Americans, the Leakey family are the best known paleoanthropologists. Mary and Louis Leakey (and now their son, Richard Leakey) established the first lineage for the ancestors to genus Homo with their discoveries in Olduvai Gorge in Tanzania. They along, with other scientists, have visited several African countries, with usually more than one locality in each country, with finds that are pictured in this diagram:

Anthropological discoveries in various African countries.

The "holy grail" for paleoanthropologists is the so-called "missing link" - the skeleton that can be considered the "starting point" for the hominids. This will likely be somewhere in Africa. Several candidates have now been found, but the experts do not agree on whether these are actually ancestral or are some offshoot in the evolutionary pathway back to the first creature than can be definitively identified as the starting point. One such candidate is named Sahelanthropus tschadensis, and is about 6 to 7 million years old.

Skull fragment from Sahelanthropus tschadensis.

From this, anthropologists can envision the appearance of Sahelanthropus, as shown below (this version is hairless but the creature likely was hairy like an ape):

Reconstruction of Sahelanthropus.

The term "hominid" goes beyond what we picture as humans - it is applied to two-legged animals that are bipedal (walk upright most of the time), which includes some of the apes. New fossil finds (generally parts of skulls and leg bones) in recent years suggest that two species are important progenitors to human lineage: Orrorin tugenensis (~6 million years ago) and Ardipithecus ramidus (4.5 m.y). Ardipithecus ramidus was discovered in Ethiopia in 1994 and is now considered to be the best documented precursor to the main line of hominids. Evidence from skeletons about half complete suggest that "Ardi" walked upright but also moved about trees. The next two illustrations show first the best example of a A. ramidus skull, next a reconstructed full skull and then a reconstructed complete skeleton from which a drawing of Ardipithecus ramidus has been produced:

Reconstruction of an A. ramidus skull
A full A. ramidus skeleton and a depiction of what it might have looked like when alive.

An informative discussion about these early hominids is found on this Wikipedia website.

The genus Australopithecus first appeared about 4.2 m.y. ago. The australopithecines are generally accepted as the progenitors of the hominids. A direct ancestor of the human race is generally agreed to be Australopithecus afarensis. The most famous of all paleoanthropological finds is "Lucy", of this species, found in northern Ethiopia (by Donald Johanson and his colleagues) in volcanic deposits dated at 3.2 million years. Here is her partial skeleton:

Lucy, the most complete Australopithecus afarensis skeleton.

The skull of Australopithecus afarensis is distinctive, in part because of its rather close resemblance to genus Homo:

An Australopithecus skull.

No complete Australopithecus skeleton has yet been found, but parts from different individuals help to fill the gaps. This illustration shows a reconstructed complete Australopithecus skeleton compared with modern Homo sapiens:

Skeletons of Australopithecus ramidus compared with Homo sapiens.

The vast majority of australopithecines and earlier hominids are known almost entirely from fossil remains found in Africa. Skeletal remains older than 100,000 years are rare anywhere else. This seems to argue for Africa as the ancestral home of those animals related to Man and to early contemporaries of Homo sapiens. There is some evidence for migration out of Africa of several genera but only Homo erectus so far can be cited as a species that left Africa before the last 100,000 years.

The latest find in the search for ancestors is Australopithecus sediba. Two partial skeletons of this new species were found in South Africa. They date between 1.7 and 1.9 million years ago. They have some characteristics of the genus Homo, so that their discovers claim that they may be transitional to that group. Others dispute this. The growing opinion among paleoanthropologists is that there may be no true "missing link" in the lineage tree. Instead there has been evolutionary development of various species among the several homonid genera (in parallel rather than series).

Skull of A. sediba child.

The genus Homo goes back to just over 2.3 million years; this branch evolved from the australopithecines (A. in the diagram) that extend back at least 4+ million years. Here is a skull of Homo habilis:

A Homo habilis skull, about 2 million years old.

This is an artist's view of Homo habilis:

Homo habilis.

Homo habilis used crude tools - stones for breaking bones, and possibly cutting tools made by chipping flint. There is debate as to whether H. habilis was a hunter (killed animals for food) or a scavenger (fed off of kills done by other animals). The species lived mostly on the ground (in the African savannah [grasslands]) but took to the trees for safety.

Homo erectus is presently held to be the immediate ancestor to modern Man. Homo erectus, who lived from about 1.8 million to 300000 years ago, was tall (more slender, and often above 6 feet in height). Homo erectus may have been the first homonid to develop a crude language. Bone remains of H. erectus have been found in Europe and Asia (Peking Man), even to Indonesia (Java Man). Just where H. erectus originated is not yet established; Africa is one possibility. Here is an artist's rendering of a group of H. erectus primitives hunting in the jungle:

A clan of H. erectus.

The last few paragraphs have introduced a lot of new information. A good overview/review is found at this website:Hominid species.

Climate played a role in the evolution and migration of hominids. Warm periods, and especially ice ages, were prime factors. This chart bears on that concept:

What would become modern humans - Homo sapiens - appeared about 200,000 years ago. Prior to that a form called archaic Homo sapiens co-existed with later H. erectus. H. sapiens probably evolved from H. heidelbergensis (as did H. neanderthalis). We show below a famous painting that represents the major "players" in Man's ancestry. Read the caption for identity of each individual:

The ancestral lineage for mankind; from left to right: Genus Proconsul (an ape which may have been bipedal); Australopithecus afarensis; Homo habilis; Homo erectus; Homo neanderthalis; Homo sapiens.

There are two schools of thought about the geographic origins of H. sapiens. One, the Multiregional group (sometimes referred to as "Eden"), considers that various strains of H. sapiens developed from Homo erectus in several regions of Asia and perhaps Europe. In this view, Homo neandertalensis (which settled mainly in Europe and the Near East) began in the western part of Asia and moved into Europe. If the Multiregional hypothesis proves valid, one or more archaic H. sapiens are the direct result. The second school is the Out-of-Africa group. Currently, this is now the more favored hypothesis. A good brief summary of the two hypotheses has been put on the Internet by Paraminder Dhillon.

In the last decade, mitochondrial DNA analysis (identifying the genes and breaking the organizational code to establish their sequence;) has led to strong evidence that H. sapiens originated in the savannah of eastern Africa. Tracing the genetics back in time has identified a baseline DNA case represented by a single individual, whimsically named "Eve" by paleobiogeneticists. Populations were small, not well intermixed, and adapted to warm climates. Based on evolutionary rates, Eve may be as old as 200000 years, but since no fossils of that age have yet been found, this progenitor may in fact be younger.

Thus, it appears that Homo sapiens began in Africa, from the Homo erectus progenitors that had settled there, and remained on the continent for about 150000 years. Some 40 genetic units lived there but were largely isolated from one another. One group is represented today by the "Bushmen" but most of the other units have died out or dispersed. There is some recent evidence that suggests H. sapiens almost died out, probably because of severe drought.

Most of the migration out of Africa has taken place over the last 60000 years. The sparsity of fossil remains has made it difficult to be precise in tracing the dispersion of Homo sapiens. These two diagrams are among several the writer found on the Internet.

One possible history of H. sapiens migration.
An Out of Africa map showing possible migration routes in the last 60000 years; from Scientific American.

Mitochondrial DNA evidence has allowed tracing of these African units both within that continent and more recent dispersion. About 60000 years ago, some of the African units left that continent (again, drought is suspected as the cause of a need to find more find and amenable environments) and entered the Middle East and western Asia. These spread further reaching eastern Asia and Australia about 50000 years ago. Some clans moved westward into Europe about 35000 years ago (where Cro-Magnon [of cave-painting fame] co-existed for a while with the Neanderthals. (The Neanderthals, stocky and robust, were at the time better adapted to live in a climate then dominated by glacial conditions; the mental picture of a "stupid" subhuman developed when an anthropologist released [about a hundred years ago] a picture of a Neanderthal that portrayed this species as a brutish caveman-like cousin to the apes has been debunked by DNA studies (the brain of Neaderthals is actually about 20% larger than H. sapiens); the smarter Cro-Magnons may have been responsible for the demise of the Neanderthals, either by interbreeding or more likely by necine force.) Others moved across the Bering Strait into North and then South America, with notable migration into these continents about 15000 years ago (there is evidence of even earlier Man in parts of western N. America). During these last 60000 years of Exodus, genetic variations gave rise to the races and strains we observe today. A major factor in development of the races was the need to adapt to changing environments that contained different exposure rates to solar Ultraviolet rays; this UV is moderated by Vitamin D that controls the adaptation of body pigments through mutations. The original race within H. sapiens is closely related to the Negro of today.

Most readers of this Tutorial know a bit about the co-existence of Neanderhals and Cro-Magnons. The latter is one of the groups of Early Modern Humans (EMH) that dispersed worldwide. The Neanderthals were once considered a subspecies of EMH but most paleoanthropologists now consider them to be a separate species (see entry on Neanderthals at this Wikipedia site). Comparisons of the skeletons of the two hominids show distinct differences:

A Neanderthal skeleton (left) compared with the taller modern man's skeleton; the lower leg is notably shorter.

The difference between a Neanderthal and a 21st Century Caucasian man is suggested by this intriguing image:

A fanciful comparison between a Neanderthal and a modern man; a gene in the Neanderthal's DNA suggests that red hair was common.

Cave wall painting is often cited as the clear sign of a distinct culture (for a summary of this art, move to this Wikepedia site. The earliest attempts at art may be markings in caves on the Nullarbor plains of South Australia. Wall paintings in southern European caves may be as old as 35000 years. This famous example, dated at 16000 years ago, is on a wall in a cave near Lascaux in southern France:

An auroch, a buffalo-like animal in a wall painting in France.

Anthropologists classify hominid pre-history using these terms: Stone age (subdivided into Paleolithic - a span over beginning more than a million years in which several Homo species used crude rock tools; Mesolithic - about 12000 to 7000 years ago; and Neolithic - 7000 to about 5500), the Bronze Age (5500 to 3200 years ago), and the Iron Age (starting about 3200 years ago). There is no evidence for when language - the use of spoken sounds to communicate ideas - began but it may have been earlier than 25000 years ago. Crop cultivations may have started about 12000 years ago.

Timeline for some of the activities of early modern Man.

Early civilizations (defined in a narrow sense as having established large groups of Homo sapiens with distinctive cultures that are recorded as written histories) began in Mesopotamia, the Nile valley of Egypt, the Indus Valley region of modern Pakistan, in the Huang He (Yellow River) valley of China, and on the island of Crete in the Aegean Sea. These peoples built cities, created writing systems, learned to make pottery and use metals, domesticated animals, and created complex social structures with class systems. Two complimentary sets of timelines for these civilizations are:

Early civilizations timeline.
Early civilizations from about 3500 to 1000 BCE.

We close this page with a rather interesting and humorous depiction of most of the accepted members of the hominids, shown side by side:

The present and past ancestors to humans; see below to link to the named individuals.

1 HOMO HABILIS ~ NICKNAME: Handyman LIVED: 2.4 to 1.6 million years ago HABITAT: Tropical Africa DIET: Omnivorous � nuts, seeds, tubers, fruits, some meat

2 HOMO SAPIEN ~ NICKNAME: Human LIVED: 200,000 years ago to present HABITAT: All DIET: Omnivorous - meat, vegetables, tubers, nuts, pizza, sushi

3 HOMO FLORESIENSIS ~ NICKNAME: Hobbit LIVED: 95,000 to 13,000 years ago HABITAT: Flores, Indonesia (tropical) DIET: Omnivorous - meat included pygmy stegodon, giant rat

4 HOMO ERECTUS ~ NICKNAME: Erectus LIVED: 1.8 million years to 100,000 years ago HABITAT: Tropical to temperate - Africa, Asia, Europe DIET: Omnivorous - meat, tubers, fruits, nuts

5 PARANTHROPUS BOISEI ~ NICKNAME: Nutcracker man LIVED: 2.3 to 1.4 million years ago HABITAT: Tropical Africa DIET: Omnivorous - nuts, seeds, leaves, tubers, fruits, maybe some meat

6 HOMO HEIDELBERGENSIS ~ NICKNAME: Goliath LIVED: 700,000 to 300,000 years ago HABITAT: Temperate and tropical, Africa and Europe DIET: Omnivorous - meat, vegetables, tubers, nuts

7 HOMO NEANDERTHALENSIS ~ NICKNAME: Neanderthal LIVED: 250,000 to 30,000 years ago HABITAT: Europe and Western Asia DIET: Relied heavily on meat, such as bison, deer and musk ox

Just in case you want to learn even more about human evolution, we provide this Internet link to the Wikipedia web site that summarizes the topic.

Now that humans have evolved into creatures with some sophistication and inventiveness, have they the ability and power to "create" life? In 2010, a partial answer to this provocative question has emerged. A group of bioscientists, led by Drs. Craig Venter, Hamilton Smith, and colleagues announced that they have produced a new species of bacterium by building up a genome using genes severed from a known bacterium Mycoplasma genitalium and then adding other essential parts from other living matter. While it is not the same as creation ex nihilo, i.e., starting from scratch, it is an important step in the human endeavor to "create life".

After this overview of the nature of life and its evolutionary progress, we need to expand our thoughts on how life may actually have originated in space, beyond just the Earth. This page is continued as page 20-12a, reached through the Next button.

Source: http://rst.gsfc.nasa.gov/