Big history

Human Evolution on the Ancestor's Trail

We have trekked through the last billion years of evolutionary time plotted on a twelve and a half kilometer trail.  At the gingerly pace of three to four kilometres per hour it took us approximately four and a half hours to cover the distance including information and rest stops.  At that pace, each average step of three quarters of a metre jumped forward sixty thousand years.  On that scale consider the following recent milestones in human evolution.

By six million years ago, (about seventy five metres from the end), early humans that had diverged from chimps had evolved upright posture and the ability to walk upright on short legs. Male canine teeth were about equal in size to females’, which indicates a significant shift in social life.

By four million years ago, (about fifty metres from the end), broad knee joints indicate clear adaptation to regular bipedal walking.

By three and a half million years ago, (about forty metres from the end), the oldest definite early human footprint trails, with footprints of other animals and environmental evidence have been discovered.

By two and a half million years ago, (about thirty metres from the end), early humans made basic tools and ate meat obtained from large animals that they hunted.  Clear evidence has been found of a double-curved spine, which indicates a shock-absorbing system associated with bipedal walking.

By two million years ago, (about the length of the PineCliff parking lot), fossil evidence of robust hip bones and lengthened thigh bones indicate that human ancestors could walk farther, faster and more easily which allowed early humans to migrate from Africa to Asia.  

By one and a half million years ago, (within the first few parking slots), the first major technological innovation of hand axes are developed and persist for another million years. 

By eight hundred thousand years ago, (the width of 4 parking stalls), early humans had control of fire and created hearths.  This heralded the beginning of the most rapid increase in early human brain size (relative to body size). The fastest pace of brain enlargement took place between 800,000 and 200,000 years ago.  This lead to prolonged maturation of the young when early human adults hunted large animals to feed their families.

By four hundred thousand years ago, (about the width of two parking slots), early humans made shelters and invented wooden thrusting spears.

By two hundred and fifty thousand years ago, (about three metres), early humans began to communicate with symbols—with evidence of the oldest known “crayons” (faceted sticks and chunks of pigment).

Modern humans (Homo sapiens) evolved in Africa around two hundred thousand years ago, (barely the width of a parking slot on this twelve and a half kilometer hike); they gathered and hunted food, like earlier human species. This estimate is based on the oldest known Homo sapiens crania and the estimated age of convergence (back in time) of all the mitochondrial DNA diversity recorded in living human populations. Three species of early humans overlapped in time with Homo sapiens. The other three species became extinct between about seventy thousand and seventeen thousand years ago.

About seventy four thousand years ago, (little over a stride ago,) humanity almost went extinct due to repeated large scale droughts in portions of Africa.  Estimates vary from 10,000 adults of reproductive age to as few as 600.  This bottleneck in human evolution reduced the genetic diversity of humans considerably.

By sixty thousand years ago, (about the length of a forearm from elbow to finger tip) cro-magnon modern humans had created permanent drawings and ventured out of Africa in waves reaching as far as Australia and Europe

The last Ice Age, which allowed humans to migrate across the Bering Straight to North America, receded about eighteen thousand years ago, (aboout the length of a man's foot) effectively isolating humans in the Americas for the next ten thousand years.

The agrarian age, beginning about twelve thousand years ago, (a distance of a stretched thumb to pinkie span), become a “turning point” in the history of life as they control the growth and breeding of certain plants and animals. Farming and herding ensue, which transformed natural landscapes—first locally, then globally. Food production led to settlement (villages, towns, cities) and population growth.

The common era for the last two thousand years, (at two and a half centimetres, it is barely the length of a thumbprint) provides us with a written history of our ancestors, how they lived and who they prayed to and has influenced the development of modern society.

The industrial age of the last three hundred years (half a centimetre approximately equivalent to the width of your pinkie nail) has seen unprecedented development of everything we see around us in modern cities and transportation. 

The extraction of fossil fuels from coal to petroleum to natural gas has released enough carbon into the atmosphere to trigger another era termed as the Anthropocene, that is, the Age of Man and a changing of the atmosphere to trigger another extinction event.

Within my life span of just a millimetre on this scale, the human population has more than doubled from three and a half billion to almost eight billion people.  Four fifths of the earth's land surface has been directly affected by humans and meat production rivals transportation for the effect on global warming.Personal responsibility coupled with governmental incentives and penalties will be needed to slow down the eventual and inevitable extinction of human life on this planet.  Switching to a vegan diet will benefit your physical and emotional health, the lives of sentient cousins and the health of the planet.

For more information:

https://www.si.edu/newsdesk/factsheets/milestones-human-evolution

Ancestor's Trail
  1. Ancestor's Trail Hike
  2. Why Is Life On Earth Carbon-Based?
  3. Metazoans
  4. 900MYA we had a common ancestry with Choanoflagellates (non-animal eucaryotes)
  5. 800mya we had a common ancestry with Sponges
  6. 780mya we had a common ancestry with Placozoans
  7. 730mya Ctenophores
  8. 680mya Cnidarians
  9. 630mya Flatworms
  10. 590mya Protosomes
  11. 570mya Ambulacrarians
  12. 565mya Tunicates
  13. 560mya Cephalocordates
  14. 530mya Agnatha
  15. 460mya Chondrichthyes
  16. 440-450mya FIRST GREAT EXTINCTION
  17. 440mya Actinopterygii
  18. 417mya Dipnoi
  19. 360-375mya SECOND GREAT EXTINCTION
  20. 340mya Amphibians
  21. 310mya Sauropsids (lizard-faced non-mammalian chordates)
  22. 251mya THIRD GREAT EXTINCTION
  23. 205mya FOURTH GREAT EXTINCTION
  24. 180mya Monotremes
  25. 140mya Marsupials
  26. 105mya Afrotheres
  27. 95mya Xenarthrans
  28. 85mya Laurasiatheres
  29. 75mya Glires (Rodents and Lagomorphs)
  30. 70mya Non-primate Eurachonta (Cologus and Tree shrews)
  31. 65mya FIFTH GREAT EXTINCTION
  32. 63mya Prosimians
  33. 58mya Tarsiers
  34. 40mya Platyrrhini
  35. 25mya Catarrhini
  36. 18mya Lesser Apes
  37. 14mya Orangutans
  38. 7mya Gorillas
  39. 6mya Chimpanzees and Bonobos
  40. Human Evolution on the Ancestor's Trail
  41. 7 BILLION HUMANS