Are we underway in our evolution to source new species from Homo sapiens? Are Sapiens splitting into different sub-species? There is a whole host of such questions. Do we have any data, which could be used to provide answers to those questions? When could we, possibly, have such data? Let us take a brief look at it.
Steady or Not So Much
The first question to ask is if the evolution has a steady pace or does it vary? If it is steady then, probably, it would be possible to calculate how far Sapiens is on its way to spring new species. If the pace varies then the situation is more complex.
The theory that biological evolution happened at approximately the same pace was prevalent for a long time. One of the problems with this theory was that fossil records do not show transition forms of living objects from one species to another.
A very rare example of small, but detectable over time, changes within the same human species was recently discovered in South Africa. The time interval was around 200 thousand years. Those anatomical changes were in the direction, which was opposite to changes that happened within Homo Erectus lineage. That is an important reminder that evolution changes could happen in different, and sometimes totally opposite directions.
Then, in 1972, paleontologists Niles Eldredge and Stephen Jay Gould proposed a new theory, which is known now as “punctuated equilibrium”. A much simplified comparison of those theories provided in the next image.
In the gradualism model at the bottom part of the image, the thick solid lines, running in just one direction, illustrate that changes from one species to another happen at a steady pace. From time to time, new solid lines, which are pointed in a different direction, spring out. Those new thick solid lines help us visualize the emergence of new species.
The illustration of the punctuated equilibrium theory is in the top part of the image. It looks very different. Every thick solid line represents the string of the multi-generational evolutionary changes of the same species. That is the state of little or no morphological change, which is called stasis, or equilibrium. The duration of stasis, also known as punctuation, varies. That stability phase followed by rare bursts of evolutionary change, during which new species formed. Thin lines on the image represent the rapid evolution stage. Every thick line represents a separate species.
Do Not Forget the Scale
An evolution discussion should include an overview of used scales. Those scales could be time scales. They also could be scales of biological classification hierarchy levels involved. Paleontologists usually talk about geological time scale. That scale is, at least, many thousands of years, and could be many millions of years. An evolutionary biologist looks at the scale of new species introduction. Or they look at a much broader scale, when new families, or orders, or classes of organisms formed.
Eldredge and Gould’s theory of punctuated equilibria is limited in scale, and relates only to the formation of new species.
There is also an alternative view that both gradualism and punctuated equilibrium theories do not contradict each other much.
The explanation is that an appearance of instantaneous change in punctuated equilibrium, in reality, is a gradual change, which happens in a short time. Some description of this view is in the article “Speciation and Bursts of Evolution“. The image above illustrates such a viewpoint. Of course, ten thousand years is “short” only on a geological scale.
We are interested in Sapiens biological evolution in the last and future several tens of thousands of years.
Data About the Human’s Evolution Timeline
What we are trying to understand is how long it takes to form a new species in the genus Homo and what do we know about the current pace of evolution of Homo sapiens in that direction.
Researchers know many members of the genus Homo now. The dates of the first appearance of those human species are roughly described in the publication of the Smithsonian National Museum of Natural History.
The following table presents the above information and data about Homo denisova.
*) Homo heidelbergensis migrated into Eurasia from Africa around 400 thousand years ago. Some of them moved into Europe and evolved into Homo neanderthalensis. The other part moved into Asia and evolved into Homo denisova.
Long Road to Become Other Specie
We could see from this table that it took approximately 400 thousand years of evolution of Homo heidelbergensis into Homo sapiens. It looks like, overall, in genus Homo, a duration between a particular specie’s first appearance and this specie’s divergence into other species is in the range of 300 – 1,200 thousand years. What does it tell us?
If we accept the graduation theory of speciation for genus Home, then we could assume that one percent of gradual evolution into the next species happens in 3 – 12 thousand years. That is a pretty slow rate for humans.
If we accept the punctuated equilibrium theory then we have more uncertainty. The total duration of the stasis plus rapid transition phases would be in the range of 300 – 1,200 thousand years. The duration of the accelerated transition to a new species is tiny compare to 300 – 1,200 thousand years.
How long could be the transition phase? “I’d be happy to see speciation taking place over, say, 50,000 years,” said Gould. That is a citation from Roger Lewin’s article “Evolutionary Theory under Fire”. Let us use 10 – 50 thousand years as a rough estimate of a transition time in a rapid evolution into the next human species. In that case, we have one percent of evolution into the next species during the transition phase happening in 100 – 500 years. That is a very fast rate for humans.
Genetics Rules the World!
According to the authors of “A global reference for human genetic variation” article, the typical difference between the genomes of two Sapiens individuals was estimated at 0.6% of the total of 3.2 billion base pairs. Those were data from the year 2015.
We could choose another genetic marker as a measure of variation within the Sapiens population. I cited in my previous post that the typical difference in mitochondrial DNA within a species, including humans, is just 0.1%. And, at the same time, the mitochondrial DNA of our closest cousin, Neanderthals, has a 1 percent difference from Sapiens.
That gives us an approximate measure of how far genetics should change in Sapiens to spring a new species. In that, post-Sapiens species, the mitochondrial DNA should, probably, differ by 10 times or more from a typical variation within Sapiens, which is 0.1%.
Is it possible for scientists to uncover data showing that we, Sapiens, are on the way to split into two species? The short answer is “it depends”.
Pace of Evolution and Genetic Measure
Here is what we should expect if Homo sapiens will gradually evolve into post-Sapiens species.
The mitochondrial DNA difference from typical variation within the Sapiens population should increase from 0.1% to 1.0% in 300 thousand years. In demography, the average time between two consecutive human generations ranges from 22 to 33 years. We will assume that it is 30 years. Our scientists would need 300,000 / 30 = 10,000 generations of people to be able to robustly confirm the emergence of new human species.
The picture would be different if (a) punctuated equilibrium theory is valid, and (b) the estimate of 10 – 50 thousand years, as a transition time of rapid evolution into the next human species, is also true. Both are big IFs.
If both assumptions are correct, then an increase from 0.1% to 1.0% in the mitochondrial DNA difference from typical variation within the Sapiens population should happen in 10 – 50 thousand years. That is within 270 – 1667 generations of people. Therefore, we should not expect any quantifiable data within several or even tens of generations of people’s lives.
That leaves us with this outcome. Any quantifiable by genetics proof that Sapiens evolution is on the way to produce new species is, probably, doomed within many generations, or tens of generations of humans, to come.
On the other hand, we should be happy that our history is still a history of just one species, Homo sapiens. At least, for now.
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