Evolution in general is a natural, continuous phenomenon that manifests differently in different species. Human evolution on the other hand becomes an unpredictable and highly debatable topic that meanders with every new study completed or fossil found. A lot of time, energy and resources have gone into researching human evolution, unlocking useful knowledge and just as many unanswered questions. A lot of our evolutionary past is certain; but our evolutionary future is elusive to predict. One thing is for certain – we are constantly evolving! This article not only gives a brief run through our evolutionary past but also tries to give an insight on the recent evolutionary changes occurring; most importantly the consistency of the evolution across different populations.
Human evolution is a lengthy process in which people originated from ape-like ancestors. Scientific evidence shows that we evolved over a period of approximately six million years. We, Homo sapiens, are part of a large human family tree containing more than 20 species of ancient human relatives (hominins).
The latest genetic evidence puts an intriguing twist on current thinking about how our species evolved - for example when Homo sapiens left Africa, rather than simply replacing archaic human species such as Neanderthals in other parts of the world, they interbred with them.
There are three main models to explain the evolutionary origins of human beings: the Recent African Origin or Out of Africa model, the Multiregional model, and the Assimilation model. Accumulated fossil, archaeological and genetic evidence supports the first view. The Recent African Origin model proposes that modern humans evolved once in Africa between 100-200 thousand years ago and that modern humans subsequently colonised the rest of the world without genetic mixing with archaic forms. This theory is given a huge boost through the discovery of mitochondrial DNA (genetic information carried separately to regular DNA) and its inheritance patterns. It showed that part of our genome, inherited only through mothers and daughters, derived from an African ancestor about 200,000 years ago. This female ancestor became known as Mitochondrial Eve. In the following decade, more genetic data both from recent human people and Neanderthal fossils were collected supporting the Recent African Origin model.
As long as there is variation in the population in terms of reproduction, there will be a difference in reproductive success – which means that natural selection can happen. This means that humans better adapted for survival in today’s world are more likely to pass on their genes to further generations. Humans are sheltered – in fact factors like globalization, improving health care and increased hygiene manage to slow down the process of natural selection. It is possible that we in modern societies have more individual freedom to express our genetic predispositions because social influences are more relaxed, and this leads to the genetic differences among us explaining more of the reproductive patterns.
There are, however, a few good examples to demonstrate our continuing evolution:
1. Drinking milk: When we began domesticating cows, sheep and goats, being able to drink milk became an advantage, and people with the genetic mutation that allowed them to digest lactose were better able to propagate their genes, as they were nutritionally better off than their lactose-intolerant peers.
2. Loss of wisdom teeth: Our ancestors had much bigger jaws to help chew roots, nuts and leaves. A third set of molars is believed to be the evolutionary answer to aid eating habits. Today, our jaws are much smaller due to our current lifestyle, which is why wisdom teeth are often impacted when they come in — there just isn't room for them in our mouths.
3. Resistance to diseases: In 2007, a group of researchers looking for signs of recent evolution uncovered 1,800 genes that have only become prevalent in humans in the last 40,000 years, many of which are devoted to fighting infectious diseases like malaria.
4. Shrinking brain sizes: The average volume of human brain has decreased from 1,500 cm3 to 1,350 cm3. Our brains shrink not because we're getting dumber, but because of efficiency. This suggests that our brains are being rewired to work faster while taking up less space.
‘Extended Phenotype’ is a recently developed concept. A phenotype is an observable trait of a gene. So hair colour, height or blood type are all phenotypes. The extended phenotype takes this a step further, into the habitat that an organism is compelled to build for itself. Just as much as a bee’s hive, or a beaver’s dam is an extended phenotype - so is human society, built by and lived in by humans. This can point out a fascinating and also incredibly worrying loop in the course of our own evolution. As our extended phenotype becomes ever more convoluted and complex, it extensively defines our environment, so much so that we are in fact now being subject to the selective pressures that we have created ourselves. As more and more human generations are born, the very fabric of our nature weakens. Our biology becomes hyper-dependent on an environment, which we (the products of our biology and environment) have created.