In part 1 of the series, “How did our ancestors survive?”, I wrote that our first ancestor is the ape that stood upright and started walking on two legs. According to the Smithsonian National Museum of Natural History this huge milestone occurred somewhere between 6 to 8 million years ago. Here is the info from its website.
Fossil and genetic evidence tells us that the last common ancestor of the humans and living apes lived between 8 and 6 millions years ago. We do not yet have its remains.
It is important to understand the process of evolution to fully comprehend the importance of this milestone. The way I understand evolution after watching the TV Series Cosmos is that evolution happens due to a copying error in the DNA. The example in the Cosmos episode was given of a brown bear giving birth to a white bear cub due to a copying error. This error propagates albeit slowly in the next generations because the white bears get a natural advantage over their brown siblings due to icy (white) conditions prevailing during that time. Slowly over many generations, the brown bears become extinct in that region and the white bears survive thus splitting one species into two. All because of a small copying error in the genetic code.
If we apply the same evolutionary process to humans, a copying error caused an ape to stand upright and start walking on two legs. Somehow, this ape coped with the prevailing conditions better than the other apes and when the genes were passed onto the next generation, the offspring that walked upright prevailed better than the offspring that did not get the copying error. It is important to note that not every offspring will get the same DNA and so it safe to assume that some offspring were still apes.
If we look at this scenario a little bit closely, the first human ancestor was living with apes and had apes as offspring. How long could it have been before there was a family with only humans? The first entirely human family. Your guess is as good as mine. Maybe, 1000 years or more. How many years before there was a small community or tribe of only humans? Maybe a million years or more.
Anyhow, here is what Daniel Lieberman in his book, The Story of the Human body writes about standing upright.
As we start our exploration of the human body’s story in order to ask what humans are adapted for, a key first question is: why and how did humans become so ill adapted to life in trees, as well as feeble, slow, and awkward? The answer begins with becoming upright, apparently the first major transformation in human evolution. If there was any one key initial adaptation, a spark that set the human lineage off on a separate evolutionary path from the other apes, it was likely bipedalism, the ability to stand and walk on two feet.
Lieberman, Daniel (2013-10-01). The Story of the Human Body: Evolution, Health, and Disease (Kindle Location 455). Knopf Doubleday Publishing Group. Kindle Edition.
Continuing a few pages later here is what Daniel Leiberman says about the Last Common Ancestor (LCA) between humans and chimps.
Alternatively, a few paleoanthropologists speculate that the LCA was a monkey like creature that walked on top of branches and climbed trees using all four limbs. These views notwithstanding, the balance of evidence suggests that the very first species in the human lineage evolved from an ancestor that wasn’t considerably different from today’s chimps and gorillas.
Lieberman, Daniel (2013-10-01). The Story of the Human Body: Evolution, Health, and Disease (Kindle Locations 514-517). Knopf Doubleday Publishing Group. Kindle Edition.
Since there is general consensus among scientists that bipedalism was the first evolutionary change that triggered a new species to evolve, the cause is not yet known. Why an ape decided to stand upright and walk is still a mystery. Was it because of a copying error in the genetic code? Or was it because an ape was a Curious George who invented a new mode of locomotion? Either way, one small change of becoming bipedal caused such a transformation.
There was not much of a social life or daily life for our first ancestor. No usage of tools or language. Not much different from a monkey in the pursuit of survival but it all started with this ancestor. This ancestor is know to belong to a group called Sahelanthropus tchandensis and may have looked like the image below.
In my next post, I will write on the ancestor who became the first hunter-gatherer and what this ancestor did to survive?
Thanks for reading and have a great day!
P.S., Links to the rest of the posts on this topic