Things that Make Us Human

Introduction

At first glance, this question may seem more philosophical than scientific. However, thanks to relatively new-found technology such as genome sequencing and fossil databases it is becoming more and more possible to approach this question from a purely scientific angle. One can look at what makes us human through multiple lenses such as classification, evolutionary and molecular levels. These are the parameters that will be used to discuss what makes us human in this essay.

Classification

The vastness and diversity of life on earth have been a cause of difficulty when trying to classify organisms and are still an ongoing process with new species constantly being found. Carolus Linnaeus is considered to be the founder of taxonomy as it was he who first suggested what is now known as Linnaean taxonomy in ‘Systema Naturae’ (Linnaeus, 1758) whereby organisms are grouped via 7 levels known as taxa( refer to figure) with the kingdom being the broadest of groups and species being the most specific. For example, Humans share their Kingdom, Phylum, Class, and Order with chimpanzees, only branching off at the family taxa (McNulty, K.P. 2016).

To what makes us human, binomial nomenclature (that was also created by Linnaeus) can begin to aid our understanding. This system uses the genus and then species taxa to give each species a name; ours being Homo sapiens (Loike and Tendler, 2002). This suggests that one of the factors that make us human is in fact a system human designed to categorize and collect data on all organisms. Furthermore, it is the actual characteristics that led to the creation of this species nomenclature that separates us from other organisms in the animal kingdom as followed:

Evolution and the genus Homo

Perhaps due to a change in brain size or human’s tendency to copy one another, around 100,000 years ago agriculture was born and soon became our main source of food supply (Wilson, 2012). This sparked the selection of a mutation ( in the form of a duplicated gene) which increased the number of salivary amylase in humans (Wilson, 2012)-meaning that our ability to digest and break down starch increased. It is this selection of the gene that shaped society as we know it today. Before this era, Humans were mostly hunter-gathers and thus traveled where ever food was plentiful; sometimes food would be scarce and sometimes it would be abundant. A shift to farming meant that human food supply whilst less diverse became more certain and stable. The stability in food supply will have undoubtedly increased the population size and rooted humans in one place. This switch to agriculture evidence that it was in fact our own behavior that resulted in the selection of the salivary amylase gene and thus our own conscious decisions have resulted in us becoming more and more human. It is arguable, however, that our conscious decision to switch to agriculture as the main food source is a result of brain size increasing and thus evolution via natural selection whereby larger brains were favored.

Molecular/ genetics

Chromosome 2

Genetically speaking, one of the most noticeable differences between humans and our closest living relatives (chimpanzees) is that humans have 23 pairs of chromosomes whilst chimpanzees have 24. On closer investigation, it has been found that chromosomes 2a and 2b in chimpanzees appear to have fused in humans resulting in one less chromosome in the human genome (Collins, F.2007). This suggests both a common ancestor and a distinct divergence between humans and the other primates all of which have 24 pairs of chromosomes (Varki and Nelson, 2007).

Chromosome 7

Another factor to consider when reflecting on what makes us human is not just the presence of a gene but the expression and variation of it. For example, the FOXP2 gene located on chromosome 7 (Maricic et al., 2012) is considered to be the gene that contributed to the progress in human speech. Whilst this gene is present in all other primates, in humans a mutated version exists whereby two substitution mutations have occurred resulting in two different amino acids that are not present in chimpanzee FOXP2 or any other primate (Enard et al., 2002). This implies that is it not the presence of new genes that make us human rather a variation in the genes that exist in many species. What is more, this evidences that the mere mechanism of natural selection could be the primary reason that H. sapiens exist? The improvement in speech and communication will have likely resulted in more effective group hunting, cooperation, and aided learning; suggesting that this variant gene increased the fitness of the human population. Thus its success.

However, in both H. neanderthalensis and H. denisova DNA some evidence of this altered FOXP2 gene have been found (Schreiweis et al., 2019). These samples may have been either contaminated by human DNA or are a product of direct interbreeding within the homo genus (Smith, 2007). If one assumes that the samples taken were valid, one can deduce that whilst FOXP2 may be a gene that makes us human it cannot be considered a gene that makes us H.sapien.