Human evolution began with primates and then 7 million years ago, the separation began.

That is how we begin our evolutionary tree.

Now we all know it starts with the proto hominins, Sahelanthropus, Orrorin and Ardipithecus followed

by the Australopithecus and Paranthropus.

Then, finally came the genus Homo.

These stages of human evolution have been discussed in our previous videos but what

we have not discuss is why these stages occurred or what made these stages take place.

Now, the most common believe is that climate change is what drove the physical changes

in the body leading to evolution.

But you will be surprised by the number of other theories and hypotheses of why evolution

occurred.

Let me begin right away.

1.

The first one is known as the Savannah hypothesis.

This hypothesis states that, hominins were forced out of the trees they lived in and

onto the expanding savannah and as they did so, they began walking upright on two feet

but early hominins have been reported to be associated with densely wooded environments

and sometimes forest, thereby reducing the importance of a shift from closed to open

ecosystems in shaping these processesrendering this hypothesis weak.

2.

Next, we have the aridity hypothesis.

This one supports the savannah hypothesis stating that the savannah was expanding due

to increasingly arid conditions, which then drove hominin adaptation.

Therefore, during periods of intense aridification, hominins also were pushed to evolve and adapt.

3.

There is one known as the Turnover pulse hypothesis.

This theory states that extinctions due to environmental conditions hurt specialist species

more than generalist ones, leading to greater evolution among specialists.Hence, when there

is an environmental disruption, thegeneralists will tend to thrive by using new environmental

opportunities and by moving elsewhere to take advantage of other areas that have lost specialist

species.

Human species are considered a generalist species considering generalist species can

feed on a wide variety of things and thrive in various environments while a specialist

species eat a limited diet and occupy a much narrower niche.

4.

Next up is the Red Queen hypothesis which states that species must constantly evolve

in order to compete with co-evolving animals around thembecause in order for a species

to maintain its relative fitnessamong co-evolving systems continued adaptation is required.

According to this theory biotic interactions,rather than climate, are driving evolutionary forces.