No Diversity in Humans, it was Toba or just Sex?

"Modern humans display less genetic diversity than great apes, a puzzling finding given our much larger census population size (1, 2). Interestingly, recent studies have shown that modern humans are not the only hominins characterized by comparatively low levels of genetic diversity. The variability of Neanderthal mitochondrial DNA is on par with that found in modern humans (3–5). More importantly, the effective population size of the common ancestor of modern humans and Neanderthals was recently estimated at 9,999 (95% CI: 9,603–10,335)*, concurring with Noonan et al.'s (6) assumption that the effective population size of the common ancestor was similar to that of modern humans, ≈104. Why are all 3 of these Pleistocene hominin populations characterized by levels of genetic diversity that are lower than those found in extant great apes?" - Culture, population structure, and low genetic diversity in Pleistocene hominins

The lack of diversity in Humans is that kind of thing that makes any evolutionist anxious for a "Natural" explanation, something in the environment that made it happen!

The Toba catastrophe theory is exactly that, the environmental cause that the holly Natural Selection must explain. Species, Sexual Selection, who cares? In the end, all it matters is Natural Selection! This is the way it must be...

I will give my own explanation for what caused the lack of Diversity in humans to the point of being almost clones (virtually identical DNA). This means that you will end up with two causes, that I named like this:

• The Toba cause;
• The Sex cause.

The Toba cause:

Simple putted, 75.000 years ago, a Supervolcano in Indonesia called Toba, erupted, causing an extreme change in the environment that led to the death of many modern humans almost to the point of extinction, and doing so, made a genetic bottleneck that eliminated the human diversity that existed before. Simple, practical, all questions answered... or so it looks like.

But not all questions were answered:

• Why modern humans, and only modern humans, lost their diversity the way they did?
• How it proves that modern humans had more diversity before the eruption in the first place?
• Why modern humans never had recuperate a bit of that diversity considering that the event happen half way the existing time of modern humans?
• Why modern human with an astronomical population size had never catch up a bit of diversity?
• Why ancient stone tools in southern India were found above and below a thick layer of ash from the Toba eruption and were very similar across these layers?

Many studies dismiss this cause, like the following:

"The Youngest Toba Tuff (YTT) eruption, which occurred in Indonesia 74,000 years ago, is one of Earth's largest known volcanic events. The effect of the YTT eruption on existing populations of humans, and accordingly on the course of human evolution, is debated. Here we associate the YTT with archaeological assemblages at Jwalapuram, in the Jurreru River valley of southern India. Broad continuity of Middle Paleolithic technology across the YTT event suggests that hominins persisted regionally across this major eruptive event." - Middle Paleolithic Assemblages from the Indian Subcontinent Before and After the Toba Super-Eruption

The reason for this hypothesis is the same as the Red Queen one. The fanaticism of Natural Selection over everything else, including Sexual Selection.

The Sex cause:

As I have been arguing in my Posts, with references to many scientific studies and publications, Sex reduces genetic diversity. So, to explain why humans lack all that wonderful diversity that pure Naturalists love so much, the Sex cause is a good place to start.

First of all considerate the following hypothesis:

• Sex is the mechanism of speciation that defines and standardizes the respective Species;
• Sexual Selection opposes Natural Selection as the first decreases diversity while the second increases it.

Supported by:

"We reviewed arguments from a diverse assemblage of biologists—ecologists, cancer biologists, population geneticists, paleontologists, molecular biologists, genome theorists, epigeneticists—who implore that sex reduces genetic variation." - Root Gorelick Henry H. Q. Heng, 2010.Sex Reduces Genetic Variation: A Multidisciplinary Review

In this moment I answered all the previous questions but one:

• Why modern humans, and only modern humans, lost their diversity the way they did?

To start with, you should see what distinguish humans (homo) from other animals:

• Upright walking and consequent liberation of the hands;
• Ability to make tools that overcame physical limitations;
• Capacity to change the Environment.

Slowly but steadily, and contrary to other animal, Natural Selection lost its initial grip on humans, leaving it to Sexual Selection alone that without opposition was able to destroy the preexisting diversity.

So simple, isn't it? Ok, I will explain slowly, step by step...

1. Homo habilis;
2. Homo erectus;
3. Homo neanderthalensis;
4. Homo sapiens (modern humans).

Homo habilis is the human species that started to lose body hair, and a good cause for it was clothing. I know that there are studies that point out the beginning of clothing 70.000 years before, but there are also other studies that say that Neanderthals used clothes, many thousand years before, so the clothing I talk here are simple furs from other animals. This means that the use of clothing was not out of reach to the Homo habilis and certainly is hand to hand with its lose of body hair.

It must be said that Natural Selection is a more critical kind of thing (life and death) than Sexual Selection, and body hair needed to protect us from cold, found its critical purpose in night and winter. So, clothing was only needed to eliminate this critical purpose of body hair, the one that really matters to Natural Selection.

This doesn't meant the end of the Natural Selection grip on humanity, no. With the decreasing of body hair close to nothing, Homo erectus changed its skin color from white to black. Yes, Natural Selection gave up body hair to Sexual Selection but took black skin color in exchange (promoted by the African Savannah). Nevertheless, the bargain was positive to Sexual Selection, better black than hairy.

With humans able to tool making, use of caves as shelter and fire making, soon Environment started to be a very different thing, acting less directly on the human animal. The relationship between humans and Nature changed from a direct to an indirect one, convergent to an environmental alienation as we have today.

With an human environment more and more alienated of the real one, new challenges emerged. In this new alienated environment, intelligence become decisive to a new and complex courtship that gave birth the Homo sapiens, well capable of the most mystified and sophisticated relationships decisive in the breeding race dictated by an ubiquitous ruler, Sex.

There is no better example of this lose of grip from Natural to Sexual Selection than the reverse of the skin color bargain as soon as Homo emigrated to north, first as Neanderthals and later as modern humans (see Why we born Racist!). This and many other traits were lost in favor of Sexual Selection, until very little remained of the original human diversity, in an alienation process that lasted more than 2 million years.

In conclusion, the greatest triumph of humanity as a Species was not hairless or even intelligence, but the lost of its diversity through environmental alienation, the triumph of our species over the rule of Natural Selection greedy to disrupt the loved dominant standard called homo sapiens.

This could end here, but a ruler is a ruler, and Sexual Selection makes its own victims from all those who don't comply with its standard...