Biology, Chemistry, Physics

What is a Human?

Part One: The Science

Humans seem pretty important, I mean, for a start it’s the only *intelligent* life form we know of… actually, intelligent is the wrong word: you could consider many animals intelligent- some use tools, some have complex mating rules, some have complex societies, some can even do basic maths and “talk back” to us. So what actually makes Humans, Humans?

The Biology

A biologist would say: humans are apex predators made of cells working together to make tissues, tissues combining to make organs, and organs combining to make the organism. We are the most modern species of the Homo genus… but may other species that could be considered ‘human’ or ‘hominin’ walked the Earth for far longer than us! A hominin is any organism of the genus homo, but also Australopithecus and some earlier genera: these last three can be considered the ‘ancestors’ of humans, and display some similarities to humans (for example they contain a gene that allowed neurons to lengthen, and some began to use fire), but are more closely related to modern bonobos, as they were of a similar size (about the size of an 11 year old human) and were probably still covered in hair. Additionally, their brain size was just 35% of what ours are today! Despite this, they are considered to be the first truly bipedal apes! Then, around 2.8 mya the genus homo evolved: the first being homo habilis. These were probably the first species of the genus to use relatively elaborate stone tools! After this came homo erectus, around 2 mya, who used fire and more sophisticated tools, eventually leaving Africa around 1.8 mya! Homo erectus are so far the longest reigning human species, as they only went extinct 100,000 to 50,000 years ago! That’s 10x as long as Homo Sapiens have been around for! Yet they probably didn’t have language as complex as ours, and most certainly not the technology! Homo erectus lasted long enough to see three more species evolve: H. heidelbergensis, H. neanderthalensis and H. Sapiens! Weirdly, they all went extinct by 40,000 years ago, which coincides with the spread of Homo Sapiens throughout the world…

Human Evolutionary tree


But I guess there is a deeper question here: what is life?


The Chemistry

A chemist would say we are an assembly or mixture of molecules whose movement, behaviour and in fact, its life comes from various chemical reactions and other atomic interactions within the body. There are 60 elements that can be found in the average human body, but 99% of your mass comes from just 6: Oxygen, Carbon, Hydrogen, Nitrogen, Calcium and Phosphorus. You may notice that the most common 4 in the body, are also in the top 10 of the universe! This is probably no coincidence. It is the interactions of these elements and molecules that explain how your cells function! One of the most important reaction is respiration, the process of creating Adenosine Triphosphate (ATP), which is a store of chemical energy that can be later released for use or more temporary storage (eg. fat). Cells also contain proteins, sugars and lipids, which are used for all sorts of things in the body, and they are made up of just a few atoms, to hundreds, all chemically bonded together!


To find out more about the elements in the universe, click one of the images below!


The Physics

And a physicist? Well first they would tell you that life doesn’t actually violate the Second Law of Thermodynamics (to do with increasing entropy in a whole system), that’s just a misconception. For most physicists, humans have little to do with their work, but the fields of Biophysics and Medical Physics, are very much the intersection of physics and biology! Biophysicists aim to understand the goings-on inside cells and tissues using physics! This is because on the nanoscale (aka very very small) atoms and molecules simply obey laws of physics! For example, electrical conductivity in neurons, structural biology, and quantum biology. Quantum Biology is the application of quantum mechanics to biological objects, and it’s super cool! It is how random DNA mutations occur, and how enzymes work! Physics is also needed to describe how energy is used and released in the body!

The Psychology

Humans can be considered the most intelligent life form on the planet, as our brains are often described as ‘capable of higher order thinking’.

But what does this *actually* mean? It means that we are able to be creative and inventive to solve not only obvious environmental problems- like how can I get my next meal, or, how can I get to the other side of this hill- but expand upon them so much that our questions nowadays are ‘how can we land on Mars? How can I get to the other side of the world for a conference tomorrow? And this requires imagination, spatial awareness and communication rarely seen in other organisms. We can communicate with hundreds of people a day, and choose our words and conversations to suit the people we are talking to!

We are also one of the few species (although this number grows with new experiments) to be truly self-aware, and toddlers are able to recognise themselves in a mirror from 18 months. Because of this, each of us has our own perspective on the world, depending on everything we have been exposed to over the course of our lives: even if you can’t actually recall an event, it probably still influenced the way you think.


If you can’t trust an atom… trust in science!

☆it’s like magic, but it’s true whether you believe in it or not!☆

See you next time!



4 thoughts on “What is a Human?”

  1. Human brain is much advanced in the processing of motor knowledge to make tools and shape structural and functional objects using learning transfer. Thanks for the writing based on biological facts and findings

    Liked by 1 person

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