J. V. Siry, Ph.D.

The Imperiled Planet

The Dominant Animal, Chapter 3Our Distant Past

an on line guide

Annie Dillard, Weasels, Pilgrim at Tinker Creek

















Our Distant Past: "A species in search of its origins."

Outline | Examples | Vocabulary | Argument | Summary

Our human family tree.



"Imagine… some 150 million years earlier"

The Origins of life

Fossil Record

The Human Line
• the chimp line split from the human line roughly 6-7 million years ago
• the spur of brain growth from about 400 cc to 1350 cc . . .was a response to ?

The Fossil Record of Culture



"The Archaeopteryx was the first missing link"

"intermediary characteristics between what, in modern times, are distinct . . . "

"in 1875 (1861) a more complete fossil was found,…"

the lizard (reptile) bird (aves) as a common ancestral species.


By analogy:

"That group, the primates, began an adaptive radiation some 50 million years ago, and human beings are one branch of that radiation."

p. 55.


The Origin of life { 56 The RNA world –chemosynthetic evidence



                                               i.     how and where life itself began . . .remains unresolved” { pages, 56-57.

"Or it may have started with the appearance of a self-replicating molecule such as RNA, a single stranded close relative of DNA, which functions in modern cells and which can serve both as a carrier of information and as a catalyst" ( that role–the catalyst–"being played by proteins in today's organisms)."


                                             ii.     surface rocks exposed to UV radiation vs. deep sea thermals


see Miller text

Fossil record


"the repeated finding of animals that had been described on the basis of fossil specimens but that later turned up alive and just as described from ancient fossils."


Coelacanths or lobed-fin fishes off of the Comoros isles and Madagascar in Africa

Wollemi pine growing in the canyons of the Blue Mountains of Australia was but a two million year old fossil specimen before.

{ page. 58

Marine ascidians


An example of marine ascidians are significant for understanding the rule of neoteny in the evolutionary past. These animals in their larval stage "free-swimming" possess a structure that is the precedent for vertebrate backbones, called a notochord; but this structure is not retained in he adult form of the organism in these species.


Fish are vertebrates.


1.    Fish-tetrapod ancestor {59-60


"the finding of a fossil fish, 375 million years old, that makes a wonderful transitional form from amphibians, which are descendants of fishes and distant ancestors of ours.…had front fins that were partly feet."

p. 59.



2. no such reversal in the fossil record”  
p. 59
"The fact is that the continuous evolution of of organisms from only relatively simple ones in the distant past to the huge variety today, including many much more complex forms, is amply documented in the fossil record."
    p. 59




Twin "trilobites, in rocks of the Cambrian period, 500 million years ago."

p. 59.

The human line

p. 60.

                                               i.     Chimpanzees and brain size: 400 cc is the ape brain's volume.

Brain size increases are enigmatic:

they require huge amounts of blood

hence they relieve the body of waste heat

they are about as large as the pelvic girdle and hence

the birth canal's circumference is smaller than the skull.



                                   ii.     Southern African Apes – Taung child , a three year old child fossil, 1924 find.


"perhaps the most stunning missing link was found in the 1920s."

"in a lime quarry" in South Africa: 4.1 and 1 million year old group of small brained hominins about 400-580 cc in volume.


1.    Human family tree is a “bush” because of the cross-breeding { 62-63

Not a linear relation of older to newer forms of hominins


Australopithecus --> homo erectus --> homo neanderthalensis --> homo sapiens

p. 62.

But, these findings confused the linearity of the earlier ideas of descent:

Ardipithecus kadabba, 5.8 to 5.2 million years old.

Ardipithecus ramidus, is 4.4 million year old bipedal ape.

Australopithecus afarensis, 3.3 million years old.

p. 62.


Hominid split from chimps 2.    7 million year old :

After the chimp and pygmy chimp lines split from ancestral human line, "our early ancestors evolved an upright posture while retaining essentially chimp like brains."

page 65 .


"And what caused the later rapid expansion of human brains over the past 2.5 million years? "

{ pp. 65-66.

Homo neanderthalensis split from homo sapiens 500,000 years ago.

yet there is evidence of Neanderthal DNA in humans


35,000 years ago Neanderthals disappear from the record.

pp. 64-65.


Fossil record of Culture

p. 66.

What do we find in the remains of hundreds of sites?

homo habilis represents the dawn of tool-making 2.5 million years ago

Olduwan from the Olduvai Gorge in Tanzania's great rift valley

Then there are two human episodes in which divergent groups left Africa for Eurasia

• one million years ago or more (1.7-1.8) were the move of homo erectus

• another was .2 million years ago (200,000) homo sapiens


There is an unimaginably complex connection between the ability to speak & the capacity for using or making stone tools


"the Great Leap Forward" is a cultural "revolution" that transpired 50,000 years ago as a precondition for modern human's contemporary dominance

p. 67.



“Interestingly, there is a connection between the ability to make stone tools and the ability to speak. Chimps. . . . but they do not have the fine hand-eye coordination that would let them manufacture stone tools. . . . 


hammer"It turns out that the same kind of neuromuscular coordination required for stone tool manufacture is also essential to the ability of our tongues to undergo the incredible gymnastics that are required to produce speech.”

P.  67.


"This common pattern of variation in evolutionary rates has long been known. In the early 1970s a situation of relative stasis followed by rapid evolutionary change was given a special name, 'punctuated equilibrium,' which some people still misinterpret as some kind of novel evolutionary process."

P.  66.

Fossil evidence is sustained not broadly contradicted by DNA & mitochondrial DNA

Fossil evidence is replete with "missing" intermediate forms

Not all habitats and species are prime for fossilization (birds no; reptiles yes)

Fossil evidence is not "disordered" over time once sequenced

Fossil specimens have on rare occasions been found persisting today

Ernst Mayr and Homo Sapiens sapiens and Human origins

Ian Tattersall and the cost of being human.


Earth  Lawrence Berkeley lab

Hall of Human Origins; The American Museum of Natural History

 Science, geology and biology on the internet


Science centric news


Geological time clock versus the Geological time spiral

previous chapter


Mayr | Thomas | Wilson | Hardin | Darwin | Margulis | Steingraber | Carr | Keller | Watson


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September 9, 2012

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