Natural selection is the concept that Charles Darwin proposed in his famous book “On the Origin of Species” in 1859 to explain the evolution of live organisms. Before Darwin, evolution was already recognized as morphological changes from ancestral species to modern species based on fossil records. Lamarck’s adoptive evolution is one of those theories. It says that God makes each species. Then, each adopts its environment based on demands. A famous example is the long neck of giraffes. Because ancient giraffes try to eat the leaves at high, their neck becomes longer.
Darwin saw that differently. He cognized that all species are connected through ancestral origins. A new species is originated from the pre-existing original ancestor. Each current species is selected by the environment from the pre-existing inheritable variation. In the case of giraffes, it is considered that modern long-neck giraffes are selected from the variation of ancient giraffes with various neck lengths.
To eat the leaves at high, shorter necks are disadvantageous, and their chance of survival will be lower. The environmental demands gradually select the ones with a longer neck.
Although the story of the Galapagos is very famous, Darwin also knew about the domestication of plants and animals, such as flowers, pigeons and others. He recognized the inheritance and variation of unique traits in domesticated plants and animals before Mendel’s discovery. He knew a cross of two distinct species cannot reproduce, called hybrid sterility. He wondered why each species appeared to adapt well to its environment. He was thinking deeply about what the species meant. Finally, he pictured life as ‘the struggle for survival.’ He perceived the individuals who disappeared during the survival struggle as a part of an evolutional process. Darwin proposed three keywords: inheritance, phenotypic variation and selection. Darwin tried to eliminate the view of teleology and agency from evolution: no goal, purpose, or intention.
The very famous phrase ‘survival of the fittest’ was not created by Darwin but by Herbert Spencer. This interpretation was suited at that time, that was, the emergence of industrialization, capitalism and imperialism. It is justifying the idea that the winner takes all. This phrase appears to represent Darwin’s idea of natural selection. However, I wonder if this is happening in nature. Without the involvement of human activities, the diversity of species generally keeps increasing in nature. No situation looks like the winner takes all. On the other hand, in the human modern society, monopoly of wealth is quite common. Something might be fundamentally different between nature and human society.
The actual natural selection in nature is ‘death or alive.’ The most important point is ‘survive to reproduce.’ As far as an individual survives, it has a chance to reproduce. Does the fittest have a better survival chance than the non-fittest? No. Actually, there is no way to measure fitness because life challenges in nature are unpredictable and inconsistent. The cause-consequence of survival can be retrospectively described, but no property can predict the likelihood outcome of the following challenges independent of the previous ones. ‘Death’ means elimination. Is there better ‘alive’ or worse ‘alive’? No. All survivors have an equal risk of ‘death or alive’ in the next unpredicted challenges and an equal chance of reproduction.
Interestingly, the fitness concept emerges if the challenges are fixed, predictable, and consistent. That is an advantageous trait to perform better in those challenges. ‘Fitness’ is the concept of common advantages for consistent, predictable challenges. In this context, it is possible to make the matrix of ‘fitness.’ The matrix predicts the next ‘death’ and ‘alive.’ It also allows us to measure better or worse within the survivors.
‘Death or alive’ challenges for individuals in their daily lives in nature are local and spontaneous. Not uniform and continuous. What is the most significant factor controlling ‘death or alive’ is whether an individual happens to get trapped in danger or not. Each challenge an individual faces is entirely independent from others and previous challenges. ‘Luck’ is the best way to describe its survival. In nature, there is no rule. Only survivors continue. There is no better or no worse. Just survive and reproduce.
‘Luck’ is the essence of survival. There is no ‘fitness’ because of no standard rule in nature. This means that natural selection in nature cannot perform as selecting-better. It only works as selecting-out something that cannot continue to reproduce in the condition at a given time. The fundamental contribution of natural selection in evolution is ‘extinction’ but not ‘speciation,’ which is making a new species.
Only through human activities it became possible to apply fixed, predictable and consistent selections. With this consistency, not only ‘death or alive’ but also ‘better or worth’ selections within survivors become possible. With very high thresholds of ‘death or alive’ selections towards better, we created domesticated plants and animals and antibiotic-resistant bacteria. To make this type of selection work, the selection criteria should be consistent for a certain period and uniformly applied to the whole population. If the selection criteria keep changing unpredictively, having the fitness matrix is impossible. The uniform, consistent and high-threshold selections commonly happen in modern human societies. In nature, only this happens at the levels of continental or global changes, often leading to massive extinctions.
Is there a winner and a loser within survivors in nature? The most essential property of living things is the continuity. If an organism cannot replicate and reproduce, life ends. We currently exist as a live organism because our ancestors successfully reproduced. Were our ancestors a winner of fitness battles? Not necessarily. Just survivors. Lucky enough and good enough to reproduce. Barely surviving is good enough if they can reproduce. You may think about battles of males for their reproductive partners. The reality of reproduction in nature is ‘first come, first served.’ We occasionally see in TV shows that two deer fight over one female. Does the loser have no chance of mating? Yes, he does! Simply by bumping into another female. Can a female choose? That is a too high risk because there is no guarantee of finding another male.
Another misunderstanding we often have is that reproductive success correlates with individual fitness. As I discussed above, there is no measurable fitness in nature but only quality controls for survival. After that, luck dictates survival. The correlation between survival and replication/reproduction would be high in prokaryotes because they do not need a partner. However, the situation is different in eukaryotes, particularly multicellular organisms. Because a partner needs to be involved in reproduction, survival and reproduction can be independent. Better survival but no reproduction and low survival but better reproduction happen in nature. Either is OK as far as reproduction is successful. The species continues. Because of successful reproduction in their past, therefore the current species exists. Importantly, reproduction is not the goal for individual organisms. But this is the reason we currently live.
Life started as haploids like the current prokaryotes, a single copy of their genome. Duplication of the copy, called replication, takes place in a monocellular organism. Then, the replicated copy is delivered to its daughter while the original copy is kept in the parent. In a prokaryote’s life cycle, the diploid state is transient. In this situation, survival and replication are almost equal. The survivors replicate. They do not need to find a partner to reproduce. Current bacteria are all descendants of the survivors.
Chromosomes are one of the most incredible inventions of eukaryotes. Beginning of sex, mating and meiosis because of chromosomes. Two haploids mate to become one diploid. Mating. The mated diploid organism has a pair of the same chromosomes. To go back to two haploids, meiosis needs to happen.
Interestingly, the diploid organism cannot simply split itself back to the original two haploid individuals. Instead, each chromosome identifies its homologous chromosome to couple them for exchanging part of their DNA sequence. Notably, the two sister organisms after meiosis are different from each other and different from their parents in terms of their genome information. Interestingly, if there is insufficient homology between the two homologous chromosomes, meiosis cannot be completed. The diploid organism cannot produce haploids anymore. However, this is not the end of the organism’s life, the dead end for reproduction. No progeny will be created.
Interestingly, three distinct strategies of life cycles are found in the current live organisms.
1. Haploidy dominant ‘haplontic’ – haploid mitoses and growth. The diploid state is transient—most fungi.
2. Diploidy dominant ‘diplontic’ – diploid mitoses and growth. The haploid state is transient. Animals. The gametes are called sperm and oocytes.
3. Haploid-diploid life cycle ‘diplohaplontic’ – both haploid/diploid mitoses and growth. Plants and some algae.
The point I emphasize above is that the success of meiosis is independent of the phenotypic traits of individuals. Without the success of meiosis, most multicellular organisms cannot reproduce except some that can perform asexual reproduction. Darwin also noticed the importance of fertility for species continuity based on the infertility of hybrids, although he did not know of fertilization, germ cells or meiosis. The importance of successful meiosis has been chiefly overlooked in evolutionary biology.
Natural selection has little contribution to speciation, creating a new species. It is worth mentioning that the definition of species is less solid than people think. A group of organisms shares and exchanges the genetic/genomic information pool. In other words, not being the same species means it cannot share its genetic/genomic information in their normal life. The key is reproductive isolation (or reproductive barrier). Ernst Mayr and others proposed seven types of barriers: temporal, ecological, behavioural and mechanical isolations (called prezygotic barriers), as well as hybrid inviability, hybrid infertility and hybrid breakdown (called postzygotic barriers). Not all reproductive barriers strictly block hybrid formation, the accidental mixture of two genomes. The current climate changes and human activities moving organisms around from one habitat to the other often cause genetic contamination of native species by invasive ones. This is because of no strict biological barrier between them.
Natural selection in nature cannot perform selecting-better. On the other hand, genetic drifts and founder effects not tied to fitness have stronger powers for creating local variations by allelic selection within survivors. However, this process only works within a single species sharing the same genetic pool.
Only humans can create consistent, uniform selections. Thus, the stabilized matrix of ‘fitness’ becomes available. Why can humans do that? We are the only species that created vested interests (or properties) that are extrinsically acquired assets in the future. Some animals have a territory, but it is not a property. The territory is only protected by the owner’s surveillance. Others can easily temporally invade it outside of its surveillance. Only humans have properties (owning something without surveillance to keep for the future). The judgement of good or bad is tightly linked with vested interests. Securing and sustaining the values of their owners for the future are considered good. ‘Survival’ is sufficient for all organisms except humans. However, humans invented languages and logic because of curiosity and empathy. The languages and logic permitted us to capture and share the past and future. This creates anticipation and anxiety. The unpredictability of the future causes anxiety. On the other hand, consistency minimizes unpredictability. The consistency shared in a group of people became a vested interest of the group. Simultaneously, this consistency permits the development of the matrix for the better. It became possible to conduct high threshold selections for the better.
This is the base of domestication and antibiotic resistance in bacteria. Both are the consequences of high-threshold consistent selections for ‘fitness.’ As a trade-off, they lose diversity. Domesticated organisms won’t survive without our help. Global antibiotic resistance in bacteria would not have emerged without humans’ overusage. If you accept that selecting better or aiming to be better is possible in nature, the view of teleology and agency would be inevitable in biology. However, without humans’ involvement, selecting better is impossible.
The concept of ‘survival of the fittest’ was favoured because it justified capitalism, modern industrialization and imperialization. The early data in population genetics and statistical mathematics supported ‘survival of the fittest.’ Unfortunately, this concept also facilitated the idea of eugenics in the early 20th century. However, these mathematical data only explain genetic drifts in a single species but not speciation. This concept presupposes that the better is selectable. The truth is that the better never exists in nature but only in human society.
Since the onset of life, the variation and numbers of life on the earth keep expanding. Biodiversity on the earth is increasing. Importantly, none of the organisms aims at reproducing, surviving or getting better. No goal and no intention. From the day1 of the first life on the earth, life exists because of continuation. Whatever methods and strategies are used, only survivors continue. This continuity keeps us alive. Although our human economic activities are somewhat similar to the process of biodiversity, they are fundamentally different. The variation and size of the economy have kept expanding since the prehistoric era. However, something is fundamentally different. A monopoly of wealth always shows up over and over. Unlike biodiversity, economic diversity is always decreasing. Because humans try to keep consistency, consistency always creates the matrix of ‘fitness.’ ‘Everyone is aiming at better’ does not exist in nature. Ultimately, ‘fitness’ is the creation of human imagination.