U4 AOS2 Topic 10: Hominin Evolution and Fossil Record

Evolution over time

Our ancestors moved from an arboreal lifestyle (living in or amongst trees) to bipedalism (an individual that moves on two legs) and this happened by the shortening of our arms and the lengthening of our legs, over this time our faces have become flatter, and our skulls have become rounder and smaller.

Hominin brains have increased in size overtime which has helped us to develop skills like planning and speech, every hominin species have a larger brain than their recent ancestors.

One of the reasons for this was the improvement in diet of the hominin species, they shifted from eating leaves to consuming more fruits and animals, and another reason was that around 800,000 years ago they started using fire to cook their food which made it easier to consume all the nutrients present in the food. 

Cerebrum is the largest part of the brain, which is responsible for functions like sensory processing, motor control, and visual learning, as the size of our brains increased the cerebrum became more, folded which help us to do a number of activities like speech, abstract thinking and planning.

Some of the differences between the skulls of us and our earliest ancestors are, a more centralised foramen magnum, shrinking of the sagittal crest, lessening of the brow ridge, flattening of the face, less protruding chin, more domed skull and smaller teeth.  

Another change that has occurred to the hominins is a change in the limb structure.

Hominins now have shorter arms, movement in the trees requires all 4 limbs to be in contact and when our ancestors started moving on the ground their arms became shorter, as our ancestors started moving on their legs their legs started to become longer, along with these changes the pelvis size also changed becoming shorter, this change in shape helped us to stand and walk upright.

 

Human fossil record

The human fossil record is incomplete due to various reasons such as, not all individuals die in conditions of fossilisation as they might decompose or be eaten by other organisms when they die. Another reason is that many rock layers are still inaccessible to researchers, so not all fossils have been found yet.

Homo neanderthalensis, commonly known as the Neanderthals were our close cousins around 40,000 and 400,000 years ago and there is evidence that breeding occurred between neanderthals and homo sapiens.

 

Neantherthals are different from us as they have a wider nose, shorter limbs, stockier build, flared rib cage, sloping forehead, an enlarged brow ridge, larger cranial capacity, and better resistance to colder climates.

Nuclear DNA studies in 2010 show around 1–4% of the human genome is identical to DNA found in Neanderthals which tells us that breeding occurred between neanderthals and homo sapiens.

In 2010 scientists discovered bones that were 40,000 years old, and these belonged to new specie known as Homo Denisova and it is believed that they interbred with a group of ancient humans.

In April 2019 a few researchers announced that they had discovered a new specie of hominin known as Homo luzonensis, this specie was discovered after a long foot bone was found in 2007 which is almost 67 000 years old. The fossils showed a mix of both ancient and modern human traits.