Subtle changes compounded over time (The 1 Percent genes: Part 2)

We usually think Neanderthals played a part in our evolution, even going as far as thinking we might carry their genes. But as you’ll soon find out, they were on a parallel road that ended a long while ago. Also, find out when our ancestors walked on two feet, used hand tools and the big deal with brains.

Part 1: Evolutionary Developmental Biology – A short history

Part 3: Mostly similar, yet totally different

Part 4: The fascinating journey of a gene

Scientists in the Evo-Devo sphere have been able to list the following as the features that need to be focused as we build the evolution chart:

  • Proportionate sizes of Brain
  • The proportionate span of limbs
  • Size and form of the Cranium
  • The shape of thorax and body
  • Longer thumbs and shorter fingers
  • Canine teeth being shorter
  • Shortened size of muscles for chewing
  • Longer periods, gestation in particular and lifespan in general
  • Skull sitting atop the vertebral column in an upright position
  • Fewer body hair
  • Pelvic sizes
  • The appearance of a chin
  • Spine in the shape of an S
  • The topology of the Brain

Our ancient ancestry

Homo habilus, a species that lived roughly 2.5 Million years ago is found have used tools, which prove enhanced mental abilities as well as motor skills. Earlier species are characterized by smaller brains, smaller bodies, legs shorter in relation to the torso and teeth being larger. The later species display bigger brain and bodies, smaller teeth and longer legs.  Since the present form of us hasn’t been around for long, much of the features that define us must have developed prior to the advent of Homo sapiens. It must be noted, however, that none of these are independent. Many visible changes like walking upright and on two feet are a result of smaller changes like those in the vertebral column, pelvis, feet, and length of limb all coming together. Not only that, being able to walk using only the feet meant the hands were free. This influenced further changes to evolve into our present forms where we exhibit great dexterity.

Australopithecus afarensis, a species that existed 3.6 million years ago was discovered to be bipedal, but with a small brain. This species is famous for a skeleton named ‘Lucy’ that was discovered in Ethiopia. The brain sizes of this and related species were about the same as a chimpanzee. Larger brains are found to be a product of later evolution. 1.8 million years ago, we see an upper shift in brain size and a similar event half a million years ago. These converge to provide the brain sizes that enable us to among other things, write this article that you are reading.

Did you know that in spite of the ongoing climate change and rise in temperatures, comparably we live in a colder period than it has been in the past 64 million years? It all started around 2.3 million years ago when the climate became more dry and cooler. This should have nudged the hominins to adapt to a constantly changing environments, which pushed the mental faculties. We observe a growth in brain size by a factor of two within 1 million years, as our ancestors started to experience changes in food and water availability, hunting tactics, and migration.

The Neanderthal puzzle

Whenever we hear Neanderthals, we imagine a close cousin of our species, larger heads and we might even assume that they influenced the genetic make-up of modern humans. Conclusive studies point in the opposite direction, though. Although Neanderthals co-existed with our ancestors, it was half a million years ago when they split from our group, before modern humans came into being. Also, it is quite confusing to see that this species went extinct even though they had bigger bodies and a bigger brain. But it must also be noted that early Homo sapiens did exist alongside Neanderthals, although only one of them lives to see this day.

A large brain in itself doesn’t mean much unless it’s large enough in comparison to the rest of the body. As an example, a whale’s brain is much larger than ours, but our brain weighs almost 20% of our bodies, a number that beats every other mammal. Also, in an adult, the brain takes up a quarter of the energy intake while it’s way higher in infants, a whopping 60%. But that doesn’t answer the question, how this change in size affected our cognitive abilities, to which Emerson Pugh, a scientist at IBM has an interesting anecdote. He says “If the human brain was so simple that we could understand it, we would be so simple that we couldn’t.” Hit a home run with that one.

Of course, those parts of our brains that control certain functions are well identified and studied upon. The cerebral cortex is the name given to the top portion of a human brain. A component within this is called the neocortex. The neocortex is a very interesting addition, seen only in mammals. Particularly in humans, this layer forms many ‘lobes’ that are important in their functions. The different lobes and their functions are listed below:

  • Frontal Lobe: Thinking, planning, and emotion
  • Parietal Lobe: Sensation of pain, touch, temperature, pressure, and taste. Also manages mathematics and logic
  • Temporal Lobe: Hearing, memory and processing emotions
  • Occipital Lobe: Processing visual data
  • Limbic Lobe: Emotional & sexual behavior and memory processing

Notes

This series is influenced by chapter ‘A beautiful mind: The making of Homo sapiens’ of the book Endless forms most beautiful by Sean Carroll.

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If you would like to learn more about Evolutionary Developmental Biology you can head over to this link: https://evolution.berkeley.edu/evolibrary/article/evodevo_01

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