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Four misconceptions about evolution

The controversy that emerged in 1859 about the concept of natural selection described by Charles Darwin in his book On the origin of species never stopped. More than ever, in the US, Turkey and other countries, religious movements strive for the teaching in Biology classrooms of the view of the intelligent design as an alternative explanation of how life works.

Opinion polls confirm that creationist or similar views are largely shared among the American population1. This distrust is explained as the result of several factors, including poor public understanding of the theory of Evolution and its mechanisms. In the public debates, even the proponents of an exclusive teaching of Evolution Theory in Biology classes seem to be quite often unfamiliar with what they want to defend2.

Yet, evolution is one of the most disseminated scientific concepts; but it has paradoxically suffered the adverse effects of this popularisation: over the decades, a series of ideas of what was the evolution developed in the public; and those ideas, rapidly transformed into preconceptions, have been deeply inculcated in the young citizen. From an early age, we are influenced by cultural references such as films, advertising, books, newspapers and debates that subtly affirm falsehoods about this theory. Let's have a quick look at four of these commonly spread misconceptions3.

A simplified explanation of natural selection. The incorrect version corresponds to a common view of natural selection, where species are seen as uniform, and react to environmental changes; the mutations that the species undergo are imagined to go exclusively in the direction of improvement. In reality, it would be much more correct to consider natural selection as the result of two phenomena: undirected mutations and non-random selection. The undirected mutations in the genome cause undirected new traits for newly born individuals (indicated by thick blue circles), and are responsible for variability among the population. The non-random selection is the process that determines if these traits help or not their carrier to have more progeny than its fellows organisms. Individuals who are not adapted to their environment will not have offspring, or have fewer of them (indicated by red crosses), while the others will spread their traits among the population. Here the population is never completely homogeneous and mutations occur randomly, but only the beneficial ones are selected. This diagram was inspired by (Gregory, 2009).

There is no hierarchy of life

Commonly, many people see evolution as describing a sort of life hierarchy, where the most basic organisms (i.e. the bacteria) would be at the bottom and the most complex (i.e. human beings) would be at the top. In that sense, evolution would have gone from bacteria, to unicellular animals, to fish, to mammals and to finally get to the human beings; from the lowest to the highest level, or from the simplest to the most complex.

But, this view of things does not hold when we try to exhaustively fill the hierarchy of life: for example, how do we determine the "higher" animal between the lion and the elephant, or between ants and bees? In fact, evolution does not describe a hierarchy of life, it is rather a description of how current living beings are related.

Natural selection, the main mechanism of evolution4, states that any being still existing today comes from a lineage that has succeeded in transmitting its genetic heritage through generations. Countless strategies to transmit genetic heritage have emerged through time, and all current organisms have their own5. In that sense, it is hard to qualify bacteria as "inferior": they have succeeded, as well as other organisms, to breed until today.

All living organisms, from bacteria to humans, to oaks and ants, are at the same step of evolution: those who are still here today and who continue to reproduce today. Evolution did not go from simpler to more complex, or from "inferior" to "superior" organisms, it went from the ancestral organisms to all current organisms.

Illustration by Renaud Helbig.

The idea of a hierarchy of nature where human beings would be at the top has been deeply instilled in Western thought, well before the notion of Evolution emerged: Aristotle had already elaborated such scala naturæ in On the soul; Carl Linnaeus used this principle when he developed his classification in his Systema Naturæ; it can also be found in Alfred Russel Wallace's work, a friend and defender of Darwin6. For many, when establishing this classification, the strength or the intelligence of an animal appears as a good way to rank living beings. But we are going to see that these characteristics are not always that crucial for natural selection.

The "law of the strongest" is not a law of nature

Is natural selection not describing a ruthless fight between individuals in order to transmit the genetic heritage? In this context, it seems logical to think that the strongest individual would be able to kill its prey, to threaten its predator and to overcome its reproductive competitors. Being the strongest looks like the best way to be the "winner of Evolution" with more food, less danger and no sexual concurrence, all of which is needed to have numerous offspring.

The problem is that usually being strong has a cost, and this cost is not worth the benefit in every context. Facing a predator, it could be more advantageous to flee quickly or to be small enough to easily hide, rather than directly face the threat; in case of starvation, better having stored fat, than having produced a large amount of muscle mass.

In fact natural selection does not go in the same direction in all different contexts: every individual is the outcome of a selection that makes it adapted to its specific environment (which includes the climate, the resources, but also its congeners and the surrounding species). If, in this environment, being the strongest in order to dominate others is beneficial for reproduction, then no doubt that this trait will be favoured by natural selection. Except that natural selection is not just a physical duel between individuals; on the contrary, quite often, the benefit goes to the quickest, the most parsimonious or the most careful.

Beings as weak as mice or sparrows have been selected over geological time; if they are still here today, it is not due to some so-called "error of nature", but because, in their environmental context, being strong is not an advantage.

So the law of the strongest does not apply in nature because there are other characteristics that, depending on the environment, can give you higher chances to survive. What really matters then, is to have the good characteristics that can help individuals survive, right ? Well... in fact, not exactly...

Survival is not the ultimate goal in natural selection

Being able to survive seems to be the key characteristic of nature. When looking at living beings, it is striking to see their universal aptitude to survival: an animal can dedicate all of its resources to escape a predator, a fallen tree can be reborn from its roots, a bacteria can respond to antibiotics threats, etc. Under this straightforward observation, it seems logical to state that survival is the ultimate goal in natural selection.

But cases of deliberate death are clearly observable in nature: in some spider species, mothers let themselves die close to their offspring to be then... eaten by them!7 This behaviour is a way to give the young the best start in life. Also known, a worker bee will not hesitate to sacrifice by stinging the animal who would come close to the hive, and this simply to protect its siblings able to reproduce (in a hive all bees are siblings) - with whom it shares a large part of its genetic heritage. In fact, even if survival is an instinct which has been largely selected by evolution; it is nevertheless not the genuine engine of natural selection, it is at most one of its by-product.

Survival is certainly a prerequisite for breeding: an animal which survives until it is able to reproduce is likely to have its genes transmitted to future generations. But beyond reproduction, if the individual is more useful dead than alive for the genetic heritage transmission, no doubt that its sacrifice will be favoured by natural selection. The question is not to know if the individual is able to survive, but rather if its survival contributes in any way to having a better chance to transmit its genes.

Natural selection does not make individuals act for the benefit of their own species.

Let us go back to the previous example of bees sacrificing themselves. Here it is a behaviour where the insect seems to have a purely altruistic behaviour, where its action has a deleterious effect on itself (in this case death) for the benefit of other congeners. Cooperation, like lionesses hunting together, is another behaviour that seems to indicate that individuals naturally tend to help their own kind. Both altruism and cooperation seem to make sense if we consider that a species is a cohesive group, which will fight against common threats, often represented as other species: bees against hornets, lions against elephants, etc.

One can note at first that the notion of species is quite delicate to handle, even for specialists. For example, if you think that a species is a group of individuals that are able to interbreed (as we are usually taught in school), you leave out the majority of life: bacteria, yeasts and other single-cell organisms that reproduce asexually8.

But more importantly, there is the problem of non-cooperative individuals. Let's take an example: in a bacteria colony, most cells seem to be altruistic. They produce and release in the medium a complex protein that is useful to consume a resource. If this product is not directly beneficial for the bacteria that has produced it, but helps all cells, and thus (and this is important) without distinction, then this behaviour would be purely altruistic: the cells use resources to produce something that anybody can use. It seems that bacteria tend to naturally help their own kind. But this simple explanation does not hold: let's then imagine that one bacteria has a mutation that makes it unable to produce the particular protein; it could then benefit from the selfless behaviour of others (by consuming the resource), and thus without paying the cost of the production of the protein. This gain of energy can be dedicated to its reproduction, it will have more offspring than its congeners. According to natural selection, after some generations, this mutation would then be largely spread among the population and the altruistic behaviour would be in decline.

With this example, we have shown that explanations like "individuals naturally tend to act for the benefit of their own species" do not allow to explain altruistic or cooperative behaviours in living beings; we need more subtle explanations. For the previous example, evolutionary biologists usually explain the emergence of these behaviours by arguments where only the purely personal interest is considered: the goal is always to better convey its genes than its congeners. Bees who sacrifice stinging predator do not do it for all the bees in the world, but only for their siblings of their hive with whom they share most of their genetic heritage9. If some animals hunt together, it is not in solidarity for the kind, but simply because the more they are, the bigger are the potential preys. If the share of each hunter is larger than what they would have hunting alone, then it is in the selfish interest of each member to hunt together10.

Conclusion

In my opinion, if evolution and natural selection principles are so difficult to pass into the public, it is because they go against profound ideas that one has about life and human beings. We would like to see ourselves at the top of the reign of life, as being necessarily the result of a selection that always brings more strength and intelligence, or as being naturally part of a cohesive group which faces adversity together. Unfortunately or hopefully, science does not always follow our philosophical views. It is not here to please us, flatter our ego, but simply to give us a coherent view of what the world is.

Bibliography

  • Alters, B.J., Nelson, C.E., and Mitton, J. (2002). Perspective: teaching evolution in higher education. Evolution 56, 1891 1901.
  • Clark, C.W., and Mangel, M. (1986). The evolutionary advantages of group foraging. Theoretical Population Biology 30, 45–75.
  • Dawkins, R. (1976). The Selfish Gene (Oxford University Press, USA).
  • Evans, T.A., Wallis, E.J., and Elgar, M.A. (1995). Making a meal of mother. Nature 376, 299 299.
  • Gregory, T.R. (2008). Understanding Evolutionary Trees. Evo Edu Outreach 1, 121 137.
  • Gregory, T.R. (2009). Understanding Natural Selection: Essential Concepts and Common Misconceptions. Evo Edu Outreach 2, 156 175.
  • Gregory, T.R., and Ellis, C.A.J. (2009). Conceptions of Evolution among Science Graduate Students. BioScience 59, 792 799.

Notes


  1. (Alters et al., 2002) 

  2. (Gregory and Ellis, 2009) 

  3. There exist many more misconceptions; some others can be found on the website http://evolution.berkeley.edu/evolibrary/misconceptions_faq.php 

  4. There exist other mechanisms for the spread of new traits such as genetic drift; I will only talk here about natural selection. 

  5. See the article of Agustín Ávila on Kinea: http://kinea.media/en/science-technology/agave-and-bat 

  6. See chapter Chap. XV, Wallace, A.R. (1889). Darwinism, an exposition of the theory of natural selection with some of its applications. 

  7. (Evans et al., 1995) 

  8. Charles Darwin was well aware of the difficulty to clearly define the notion of species. He dedicated the entire 8th chapter of his book to this topic (Darwin, C. On the Origin of Species (1859)) 

  9. It is kin selection. See for example (Dawkins, 1976); 

  10. In fact, this example is even richer in terms of natural selection. See (Clark and Mangel, 1986).