How humans emerged in their present form


This page discusses human evolution over millions of years. This perspective does not fit the thinking of some religious movements and you may prefer to pass it over if you are a Creationist.

Otherwise, over 60 million years ago, the dinosaurs ruled the globe.

Human origins

Mammals, from whence humans came, kept a low profile at that time, and they were of small build. They were able to survive underground, through many nuclear winters, after the dinosaurs became extinct. As far as is known, the Earth received a direct hit from a large asteroid and this created a mass extinction event.

It had global impact on life and rock formations (and is known to geologists as the “K/T event”).

At even earlier times, 100’s of millions years before, mammals themselves did not exist. Reptiles ruled the roost – in the seas and on the land in later years.

Modern mammals still possess an ‘inheritance’ from these reptilian ancestors – namely, our brain stem and our cerebellum.

This reptilian brain, in the darker shade, below, still keeps us functioning without conscious thought; our breathing, and heart and sleep patterns, are monitored and regulated 24/7.

Older and not so smart sibling

In other parts of the website, I have referred to the reptilian brain and the early mammalian brain as the ‘older, and not so smart sibling’.

These are labelled in a diagram, below,  that helps to identify the ‘reptilian’ brain, from the early mammalian brain, and our modern human brain (labelled by me as the ‘‘smarter and younger sibling’).

source: Kaja Nordengen Your Superstar Brain

The history that follows is arguable, and better researchers than me are well able to offer a rather more diverse set of possibilities. Even so, what follows is a rough approximation and I prefer that to some contentious sense of  ‘accuracy’. 

A quick history covering a few million years

Let’s simply say that the early mammalian brain had a lot of ‘add-ons’ – a bit like Microsoft Windows –  with a reptilian base that evolved over tens of millions of years until, around:

4 million years ago: early hominids, now a class of mammal, started to walk on two legs. These hominids possessed a brain weighing less than a kilo.

2 million years ago: homo habilis began working with tools.

1 million years ago: homo erectus saw the brain gaining weight to about 1 kilo; with enough capability to manage fire and develop hunting techniques.

Less than 1/2 million years ago: homo sapiens, modern ‘humans’, emerged with further development of the brain, then weighing almost 1.5 kilos. There is evidence of ‘thinking’ and creativity.

Only a little over 100 thousand years ago, homo sapiens, the even more modern human, began to generate concrete evidence of abstract or symbolic thought culminating in evidence of jewellery-making appearing less than some 50 thousand years ago.

As far as we can tell, that ability evolved to permit the complex erection of structures such as the Pyramids less than 5 thousand years ago.

There are arguments about these dates as there is some suggestion that other ‘mass extinction’ events swept aside earlier evidence of creative communities of humans.

Our own moon was created by another major collision between Earth and a stray planet very early on in the story of our solar system.

Size does not matter

Other mammals, dolphins and cows, have a brain of similar size to humans but the human brain shows an ability to innovate. For instance, the brain of the Blue Whale is around 8 kilos, considerably bigger than our own (but it does have to manage a body weighing some 170 tons!)

When it comes to creativity and innovation, what seems to make the difference are the number and size of the neurons in the brain. I am told there are some 86 billion neurons in a modern human brain, with only 16 billion located in the cerebral cortex (the ‘smarter and younger sibling’).

It is in the number and location of our neurons that human beings stand out from other animals.

The social engagement system

It would appear that we owe our success, as a species, to:

Stephen Porges uses the expression – the ‘social engagement system’. It emerged from changes to the Vagus nerve, an ancient control mechanism. He labelled that social engagement system the Ventral Vagus as it worked in and around the upper part of our body.

By contrast, the more ‘primitive’ Dorsal Vagus operates in the lower body. Rather similar to the ‘reptilian’ system, the Dorsal Vagus reacts in moments of crisis. To manage severe threats, we can revert to strategies that a reptile uses efficiently e.g. slow rates of breathing.

The tricky thing is that mammals are warm-blooded creatures and experience side effects when the Dorsal Vagus is triggered. These responses contribute, at least in part, to our troublesome responses to trauma.

Flight and Fight

Elsewhere, I have discussed the detailed workings of different brain parts,  For the present, suffice it to say that one key area that has much impact on our modern behaviour is the amygdala.

This limbic nucleus,  and the Vagus nerve,  play a key role in deciding whether – in an instant – we will fight, fly, freeze or faint in order to stay alive in the face of threat.

It is the impact of these aspects of a nervous system that play a large part in our survival, and in sustaining emotional and bodily regulation in the face of threat. Called on too frequently, and the amygdala starts to play up.

How can small safe experiments respond to millions of years history?

Much of this website is devoted to small, safe experiments intended to make us more aware of the behaviour generated by this ‘not so smart and older sibling’.

If I had one intention in constructing this website, it would be:

Some other pages on those safe experiments

Practical relaxation

Controlled breathing

Body Scan

Just noticing

Categories of safe experiment

Why ‘small’ is beautiful

These pages contain specific suggestions. You may want to read more widely so …..

Other lead to consider might be

What is a Nudge

Following the scenic route

The autonomic system

Neuroscience and safe experiments

An Index of all pages on Your Nudge