Natural selection is a type of organic order which helps to shape evolution. We as humans have removed ourselves from natural environment so do the pressures that force adaptation in all other species still apply to us?
What is evolution?
The scientific definition of Evolution…….
“The changes in the heritable traits within a population across many generations.”
“Species change over time, give rise to new species, and they all share a common ancestor.”
This all started with single-celled organisms (similar to bacteria) that attempted to make exact copies of themselves, however some of them made errors in the DNA code during the copying process.
This is how the first MUTATIONS occurred.
These mutations are random and created the first variations amongst individual cells. These random mutations were passed onto to the next generation of copies.
Everything living is a MUTANT!
The evolutionary process in multicellular organisms such as ourselves, has another layer of complexity. We still undergo random mutations such as when our cells make errors when copying themselves or by harmful environmental factors such as U.V. radiation.
We are also a product of an evolutionary process called recombination, which is how scientist say: “the mixing of DNA from both parents”. This mixing is completely random and thus creates a completely unique individual every time.
Therefore, multicellular organisms receive their unique traits from their parents and from any random DNA mutations that may occur.
Although individuals of the same species often closely resemble each other, each has a unique set of DNA and therefore traits. These unique individuals meet other individuals with unique traits and give rise to more unique individuals.
This process makes all multicellular that arise through sexual reproduction UNIQUE!
At first it appears to be completely random, meaning in theory humans should be able to evolve a subspecies with three heads.
However there is a force guiding random evolution that creates an organic order……..
Natural selection by Darwin’s order
Darwin most famously detailed that NATURAL SELECTION determined EVOLUTION. Natural selection is spurred on by a form of competition known best as “survival of the fittest”, which translates to survival of the organism best equipped to make copies of itself.
This widely accepted theory recognizes that individuals vary, and certain variations can better suit individuals to the role they occupy within their ecological niche. This boosts their chances of passing down these traits to future generations.
Unknown to Darwin certain mutations in the individual’s DNA are what caused certain traits to be heritable and thus able to be passed to offspring. These mutations can be positive, negative, or neutral, and may cause changes in the individuals morphology, physiology, phenology, biochemistry, structure and behaviour.
The negative mutations make the individual or it’s offspring less adapt for survival and reproduction so usually die out within a generation or so. The positive mutations are the ones that better able the offspring to survive and reproduce, thus making them more likely to reach future generations.
This process creates traits unique to individuals, and eventually adaptations in species, that make them fitter for survival. Over extended periods of time this process can even evolve entirely new species.
There are a number of factors that affect the survival and reproduction of individuals and thus influence which traits are favourable.
These include but are not limited to disease, how well an organism is able to compete for resources with individuals from the same species “intraspecific competition”, how well an organism is able to compete for resources with individuals from other species “Interspecific competition”, predator prey relationships, and how well it is adapted to survive and navigate the abiotic (non-living) factors of its environment.
Predator prey relationships aka the evolutionary arms race
One of the most fascinating relationships that spur evolution is that of predator and prey. Predator prey relationships have been famously dubbed the evolutionary arms race as levels of defence and counter-defence must continually escalate for species to survive.
Evolutionary speaking the deer (prey) must stay one step ahead of the wolf (predator) if it is not to end up a meal. The wolf must stay one step ahead of the deer if it is not to go hungry.
Deer that are fitter to escape the wolves are more likely to survive and possibly pass on those desirable traits to their young. Similarly, wolves that are fitter to catch deer increase their chance of survival and reproduction, possibly allowing the next generation of wolves to also possess these traits.
Over many generations wolves have become more effective hunters and deer have become more elusive prey.
This looks very much like competition in the short-term but in the long-term these species actually help each other thrive but that is a story for another day.
Homo Sapiens the ultimate predator
How do predator prey relationships affect humans?
For the largest part of our evolution humans were involved in predator prey relationships. Hunter-gatherers predated a multitude of species and on occasion would have been predated upon themselves.
The interactions they formed with their prey over many generations may have selected traits such as speed and endurance for tracking and capturing prey, manual dexterity for creating tools and setting traps, accuracy and co-ordination to better enable the individual to use projectile weapons, and many other favourable traits. Cognitive and behavioural adaptations would have evolved alongside physical traits.
Interaction with species that predated humans would have also caused adaptations. Traits that helped the hunter-gatherers to avoid, escape or kill his would-be predators would have been favoured. Behavioural traits such as a curiosity for species with large teeth and sharp claws would have quickly been weeded out of the gene pool.
Predator prey relationships which involve humans are almost non-existent in the modern world. Most of us have little contact with any wild species let alone predator prey relationships. Most of us no longer predate other species, and other species are not given the opportunity to predate us.
Even the traits in the farmers who are involved in most of our food production have little chance to be favoured or omitted in terms of predator prey interactions.
It is almost a certainty that the farmer can harvest his crop or send his animals to slaughter. Collective knowledge and technology play a far greater part in the farming of animals than the farmer himself. At least in regard to predator prey interactions.
There is no game of capture and escape, so traits that favour these conditions would not persist in subsequent generations.
Since humans removed themselves from natural ecosystems and began to create their own habitats they gained a permanent upper hand over all other species. This has effectively completely removed them from the evolutionary arms race.
Interspecific and intraspecific competition
Competition not only occurs within the same species (intraspecific), but it also occurs across different species (interspecific).
Intraspecific competition occurs when individuals of the same species compete for MATES and LIMITED RESOURCES such as space, food and water.
Interspecific competition occurs when two or more species compete for the same resources as with intraspecific competition. Generally, the more similar the species are the more intense the competition. Think of a forest where many different species of tree compete for sunlight, or an African savannah where lions compete with hyenas for prey.
Both intraspecific and interspecific competition can happen directly (interference competition) or indirectly (exploitive competition).
Interference competition can take the form of fighting, stealing, and ritualised combat. Ritualised combat was and is practiced by a number of human tribes to win mates and resources.
Exploitative competition occurs when individuals or species indirectly compete for limited resources. The classic example is treed competing for sunlight. Those that photosynthesize the most sunlight usually grow taller and overshadow other plants reducing their fitness.
Intraspecific competition is recognized as one of the main drivers of evolution. Competition between members of the same species for limited resources mean there are both winners and losers.
The losers may not survive and reproduce meaning their genes will not be passed on to future generations. This creates fitter populations in the long-term.
The same is true for interspecific competition which can sometimes lead to one species completely replacing another.
Humans Vs Human – Is intraspecific competition still relevant?
This poses the question does intraspecific competition still operate across modern humans in terms of evolution?
In terms of survival most of us are not subject to competing against each other for resources (intraspecific competition) in the modern world. Most of us have adequate food, water, and shelter to survive. As we don’t need to compete for these essential resources traits that would have favoured this competition are not likely to persist.
In addition, during intraspecific competition for favourable adaptations to persist to subsequent generations and negative adaptations to parish, there must be some winners and losers in the game of survival and reproduction.
In the modern world thanks to our large-scale co-operation, medical, and technological advancements the vast majority of us are able to survive and reproduce. There is no natural selection process, at least in regard to intraspecific competition to determine who is afforded this right.
This is not to say the modern world is without competition between humans and therefore perhaps a version of intraspecific competition, quite the opposite actually, only that this competition is no longer geared towards our survival needs. The developing world however is still subject to this form of competition.
As there is no competition related to survival between humans, both favourable as well as unfavourable traits remain within the human species.
For example, individuals carrying a mutated version of low-density lipoprotein receptor-related protein 5 “LRP5” gene are known to have stronger and denser bones compared to the average person. This makes them more resistant to breaking bones and skeletal degradation related with age. Evolutionary speaking this is advantageous as it makes the individual less susceptible to serious injury and would therefore promote survival. That is as long as they don’t try to swim, those dense bones make for sinkers ;).
Less favourable genes that still persist in our populations include those that play a role in short or long sightedness. 77% of people in the UK wear glasses or contact lenses. Disregarding age-related sight degeneration, it is unlikely the genes that give the individual less than ideal vision would survive long in nature.
Those who had not yet reproduced but had sight deficiencies may have struggled to find food, been eaten by predators, or walked themselves of cliffs. This would prevent the gene from reaching future generations. This is likely why we rarely see animals that rely on sight for hunting or evading predators with sight deficiencies. Natural selection does not favour sight deficient individuals or species. At least those that are diurnal and live above ground.
Fortunately, humans have been able to use their ingenuity to overcome many debilitating genes that would have once proved fatal in nature.
Man Vs animal Interspecific competition
Interspecific competition is the competition between different species for limited resources. This can result in the exclusion of one of the species or in their co-existence.
Interspecific competition with Human’s can be looked at in two ways. The first being that humans are in a continuous competition with all other species for the resources the planet holds.
We are continually evolving new technologies to prevent other species from consuming our food, as is the case with pesticides and pest.
We are in a continuous battle with all other species for space. Many species are continually culled to prevent them trespassing on human territory. Urbanization removes and displaces the majority of other species from their habitats. Even the concrete we continually lay is a competition against the weeds and plants that wish occupy the habitat.
In this sense humans are truly the kingpins of interspecific competition. We compete with everything and we win.
In another sense it is almost unfair to call it competition. Human’s cognitive abilities evolved more rapidly than any other species. Would we call the unarmed man facing the villain with a bazooka a fight? Other animals do not stand a fair chance to compete for resources whether it be habitat, food or water.
Evolutionary speaking humans certainly do not need to continuously adapt to stay one step ahead of the competition from other species.
We have not only won, we have cleared up.
The “win” naturally doesn’t take into account our need for other species for our own survival, but we will leave that for another article.
The multi coloured fox
Another component that is driving natural selection is the environment.
Environmental factors such as the type of biome, terrain, temperature, humidity, availability of water and weather extremes causes individuals with traits that favour these conditions to survive. Eventually evolving entire species with these adaptations.
This is perhaps best illustrated by foxes belonging to the genus “Vulpes” which can be found in almost every kind of habitat. There are 12 true species belonging to this genus and each have different adaptations that better suit them to their unique environments.
The Arctic Fox “Vulpes Lagopus” has a snow-white coat during winter to camouflage it against its frozen surroundings. After the ice has melted the Attic fox adopts its summer coat which is a dark grey/brown which acts as camouflage against the rocks and vegetation. These adaptations are not just for show, they make the fox a more effective hunter.
To thrive in the freezing conditions of the tundra the Arctic fox also evolved thick fur, and a small round body to minimize heat loss.
This is in accordance with “ALLENS RULE” which predicts endothermic animals with the same body volume should have different surface areas depending on the temperature of their environment.
Animals living in colder climates should have low ratios of surface area to volume whereas animals living in warmer environments should have higher ratios of surface area to volume. There are however exceptions to this rule.
This is perhaps why the Fennec Fox “Vulpes Zerda” which inhabits the Sahara Desert has instead evolved large ears to help dissipate body heat during the day.
Unlike the snowy coated Arctic Fox, the coat of the Fennec Fox matches the desert it inhabits.
The environment that the species inhabits is a huge driver determining natural selection. Which leads to the question are humans still adapting to their environment?
Environmental adaptation in Humans
Traditionally humans were not excluded in regard to environmental adaptation. Most noticeably we have evolved different skin, hair, and eye colour which reflect the climate we inhabit.
Humans are believed to have originated in Africa where direct sunlight is received almost year-long. This created a strong natural selection pressure for dark skin to evolve, as dark skin contains more melanin which helps to protect the skin against harmful UV rays. Those with dark skin were more likely to survive and reproduce increasing the likelihood these genes reaching future generations.
As humans moved into the northern latitudes selection pressures for dark skin became weaker. This meant genes were more likely to mutate, (such as the mutated gene responsible for white skin) and be passed onto future generations. Light skin became more beneficial as it enables the individual to absorb more vitamin D in lower levels of sunlight. Meaning those with lighter skin were more likely to survive and reproduce in these darker colder habitats.
Similarly, to other species humans also often conform to Allen’s rule. Individuals living in areas with lower temperatures tend to have proportionally shorter limbs for their height to reduce heat loss. Contrasted to those living in warmer regions which have proportionally longer limbs for their height to encourage heat loss.
This poses the question if modern humans are still evolving in relation to their environments? After all, now we have the ability to control the temperature of our immediate surroundings with technologies such as central heating and air conditioning.
We don’t use our physical bodies to navigate our urban environments as much as we use oil powered machinery. The urban environments most of us inhabit cannot be considered natural as they are removed from nature.
So although we may still be adapting and evolving to our new environment is it still via natural selection?
Natural or Human selection?
Whether or not humans are still subject to natural selection all depends on what we define as natural selection. If we define natural selection, as the pressures caused by the natural landscape and wild species that inhabit it, forcing adaptations in species over time, humans are no longer subject to “natural” selection, or at best subject to a drastically reduced version than our hunter-gatherer ancestors.
If we include artificial habitats, technologies that accompany them, and behavioural interactions that exist within the dominant culture as well as individual choices, as a form of natural selection then the answer would be yes.
It is not that humans are no longer adapting and evolving, only that we are adjusting, adapting, and will eventually evolve to a habitat that can be considered anything but natural.
For example, it has been predicted that by 2050 nearly 50% of the population will be short-sighted, therefore unable to focus on objects far away. The number currently stands at 34%. The increase is estimated due to the increased amount of time spent staring at screens and the reduced amount of time spent in nature.
Will humans eventually adapt and evolve not to be able to see over long distances and have traits that favour looking at screens?
Perhaps we should name this evolution via “human choice selection” rather than natural selection?
In the past rapid evolution occurred when there was rapid environmental change. Seeing as humans have influenced, transformed, or destroyed every habitat on Earth in such a short space of time it is no surprise that many non-human species that have survived so far will be forced to adapt and evolve or face extinction.
As for humans we have the choice upon whether we wish to adapt to our urban environments or natural environments. For now, at least!
Do we wish to incorporate ourselves back into natural ecosystems and in many generations see humans become better adapted to navigating them? Or perhaps we would prefer to see humans adjust and eventually adapt to sitting on chairs for prolonged periods of time and staring at screens?
Never before in history has a species had a choice in which direction it wishes to evolve. We can choose to adjust to urban environments or we can choose to adjust to natural environments or both. In any case our choices will echo the adaptations in the generations to come!
(To keep this article from being too lengthy I didn’t discuss a number of other factors that affect natural selection such as geographical barriers, genetic drift, and disease. I also never discussed the importance of co-operation in evolution which is arguably more important than “natural selection” especially for humans.)