Biology Online is a Biology blog and dictionary site that provides up to date articles on the latest developments in biological science. The Biology Online Dictionary is a completely free and open dictionary with over 60,000 biology terms. It uses the wiki concept, so that anyone can make a contribution.
Tag: evolution

On Mate Selection Evolution: Are intelligent males more attractive?

A study published in Science on January 11 seems to be the first to lay empirical evidence that concur with Charles Darwin’s hypothesis: … that mate selection might have contributed to the evolution of intelligence or cognitive abilities. Scientists from China and the Netherlands collaborated in a study on budgerigars, Melopsittacus undulatus. Based on what they observed, problem-solving skills apparently increased the attractiveness of male birds. Accordingly, female birds chose to spend more time with male birds that appear to be smarter.[1]



Darwin on mate selection

In animal kingdom, mate selection is a real deal. One of the generalized traits that distinguish the animal from the plant is the former’s tendency to select a mate. Animals, including humans, have their set of preferences when it comes to choosing a mate. While plants chiefly let nature do the “selection” for them, animals tend to seek a potential mate by themselves. And when they find a suitable mate of their choice, they often make a conscientious effort to succeed at coupling. In particular, males engage first in a courtship ritual, for example, by wooing a female with a song, a dance, or by a display of beauty or prowess.


Sexual selection evolved as one of the means of natural selection. A male, for instance, chooses a female to mate with, and, if need be, may tenaciously compete against other males to stack the odds in his favor. Charles Darwin’s long-standing theories on sexual selection are still relevant to this day. Darwin believed that sexual selection had a key role in how humans evolved and diverged into distinct human populations.[2] In view of that, sexual selection could have contributed as to how intelligence evolved.




Intelligent males, more attractive


budgerigars on mate selection
Female budgerigars (also called parakeets or budgies) apparently prefer smarter mates, according to a study. This finding seems to support Charles Darwin theory on mate selection.


Many studies on birds revolved around the notion that female birds favor male birds with vibrant feathers or stylish songs. A recent study claims that intelligence is preferred over such fancy features and skills.


In the first experiment conducted by Chen and colleagues[3], small budgerigars (Australian parrots) were observed inside their cages to test the hypothesis that intelligence might affect mate selection. To do that, they allowed each female budgerigars to choose among a pair of similarly-looking male budgerigars to interact with. The chosen males were called preferred whereas those that were not were referred to as the less-preferred. Next, they trained the less-preferred males into learning a skill that opens closed lids or boxes. They, then, allowed the female budgerigar to observe the less-preferred male demonstrate the skill. Consequently, almost all of the females changed their preference. They chose the less-preferred males over the initially preferred males.


To test if this preference was social rather than sexual, they conducted a second experiment with a similar experimental design but this time a female budgerigar was exposed to two females (instead of males). The results showed that none of the female budgerigars changed their preferences. [1, 3] Based on these experiments, the researchers concluded that the demonstration of cognitive skills altered mate preference but not necessarily social preference.


Video of the animal model, male budgerigar that learned a problem-solving skill that seemingly increased its attractiveness to females. [Credit: Hedwig Pöllöläinen].




Why did mate selection evolved? The answer could be associated with the species survival or longevity. Individuals must be able to stay in the mate selection pool, if not on top of it. In general, males deemed as superior or “preferred” will gain higher chances at mating, and thereby will have better opportunities at transmitting their genes as they dominate the access to fertile females. Females, on the other hand, gain an upper hand from the mate selection by being able to choose the seemingly finest among the rest. Females must choose. That is because they have a generally limited reproductive opportunity to give life to. Moreover, the energy that a female invests in producing an offspring is so great that it has to be worth it.



— written by Maria Victoria Gonzaga





1  Chen, J., Zou, Y., Sun, Y.-H., & ten Cate, C. (2019). Problem-solving males become more attractive to female budgerigars. Science363(6423), 166–167.


2  Jones, A. G., & Ratterman, N. L. (2009). Mate choice and sexual selection: What have we learned since Darwin? Proceedings of the National Academy of Sciences106(Supplement_1), 10001–10008.


3  GrrlScientist. (2019, January 11). Problem-Solving Budgies Make More Attractive Mates. Forbes. Retrieved from


Blindness – Evolutionary regression? Maybe not!

The recent Netflix’s hit flick, Bird Box, surely startled the viewers with the thrilling scenarios revolving around the precept that once seen, expect an abrupt ferocious death. Given that, Malorie (the protagonist portrayed by Sandra Bullock) blindfolded herself and the two children, and embarked down the perilous river to seek a safer refuge. (N.B. If you have not seen it yet, you probably need to pause to dodge the spoilers ahead.) Ultimately, they reached the haven, which was revealed to be an old school for the blind. The surviving community was a population of primarily blind, and as such, immune, people. By and large, this film emanated a message to me that blindness should not be taken as an utter handicap but a trait that tenders a likely evolutionary edge.




Blindness defined

Blindness is a complete, or a nearly complete, lack of vision. Basically, two major forms exist. A partial blindness means a very limited vision. In contrast, a complete blindness means a total lack of vision — not seeing anything, even light.1




Causes of blindness

Some of the common causes of blindness include eye accidents or injuries, diabetes, glaucoma, macular degeneration, blocked blood vessels, retrolental fibroplasia, lazy eye, optic neuritis, stroke, retinitis pigmentosa, optic glioma, and retinoblastoma.1


Congenital blindness refers to a condition wherein a person has been blind since birth. In fact, several instances of infant blindness are due to inherited eye diseases, such as cataracts, glaucoma, and certain eye malformations. In this case, genetic factors play a role. Retinitis pigmentosa, for example, is a hereditary condition. The retinal cells slowly disintegrate and ultimately leads to an incurable blindness later in life. Albinism also leads to vision loss in which, at times, reaches the category of “legally blind“.


The mapping of the human genome led to the identification of certain genetic causes of blindness. Scientists recently identified hundreds of new genes associated with blindness and other vision disorders. Bret Moore and colleagues found 261 new genes linked to eye diseases.2 Furthermore, they said that these newly-identified genes from mouse models likely have an analogous counterpart gene in humans. Thus, their findings could shed light in identifying the genes causing blindness in humans.



Eye evolution

Humans evolved eyes that enabled sight or vision. About 500 million years ago, the earliest predecessors had eyes that could detect light from the dark. This early eye, called an “eyespot“, could sense ambient brightness (but not shapes), which sufficiently helped orient single-celled organism (e.g. Euglena) to circadian rhythm and photoperiodism, and of course to food.3


Soon, the eyespot evolved into a rather complex light-detecting structure, such as that found in flatworms. Their eyes could detect light direction. Also, their eyes enabled them to seek a better spot to hide from predators. As light was able to penetrate the deep seas, organisms such as Nautilus evolved pinhole eye. A small opening on it allowed only a thin pin of light to enter.  This dramatically improved resolution and directional sensing.3


The pinhole eye evolved lens that regulated the degree of convergence or divergence of the transmitted rays. Furthermore, the lens helped distinguish spatial distance between the organism and the objects in its environment.3


A modern human eye has become more intricate by the presence of other eye structures. For instance, a transparent layer called cornea covered the opening (pupil) of the eye. This caused the inside of the eye to contain transparent body fluid called  vitreous humor. The iris is the colored part near the pupil. The light-sensitive membrane, retina, contains the photoreceptor cells, i.e. the rods and the cones. Apparently, the evolution of the human eye concurred with the evolution of the visual cortex of the human brain.3

eye structure
Illustration of the eye with labeled parts.
[Image credit: National Eye Institute, National Institutes of Health.]




Blindness – an evolutionary regression or a gain?

blindness eyes
Is blindness an evolutionary regression?
[Photo by omar alnahi from Pexels]


Should blindness be considered an evolutionary regression or an evolutionary gain? Blind beetle species that live in light-less caves, in the underground aquifers of Western Australia and the eyeless Mexican cave fish are some of the animals that once had a sight but lost it over millions of years.


Simon Tierney from the University of Adelaide offered an explanation to this seemingly evolutionary regression.4  Accordingly, the loss of sight in the cave fish species apparently led to the evolution of increased number of taste buds. In particular, pleiotropy might explain this manifestation. A pleiotropic gene, in particular, controls multiple (and possibly unrelated) phenotypic traits. In this case, the gene responsible for the eye loss might have also caused the increased number of taste buds. The eyesight may not be imperative in a light-deprived habitat; however, an amplified number of taste buds for an improved sense of taste is. Douglas Futuyma of the State University of New York at Stony Brook explained: 4


“So the argument is these mutations are actually advantageous to the organism because the trade off for getting rid of the eye is enhancing the fish’s tastebuds. It really looks like these evolutionary regressions are not a violation of Darwin’s idea at all. It’s just a more subtle expression of Darwin’s idea of natural selection.”




Heightened senses

In 2017, a research team posited that blind people do have enhanced abilities in their other senses. To prove this, they brain scanned blind participants in a magnetic resonance imaging (MRI) scanner. Accordingly, the scans revealed heightened senses of hearing, smell, and touch among blind participants as opposed to the participants who were not blind. Moreover, they found that blind people had enhanced memory and language abilities. Lotfi Merabet of the Laboratory for Visual Neuroplasticity at Schepens Eye Research Institute of Massachusetts Eye and Ear said:5


“Even in the case of being profoundly blind, the brain rewires itself in a manner to use the information at its disposal so that it can interact with the environment in a more effective manner.”





As the popular maxim goes, the eyes are the windows to the soul. In the presence of light, our eyes can perceive all the seemingly playful colors and spatiality that surround us. At times, a simple stare is all it takes to convey what we could have said in words. Despite the loss of sight in some of our co-specifics, their brain configured into an avant-garde stratagem that enabled them to do most of what a seeing person could. Based on what the researchers observed, they had enhanced interconnections in their brain that seemed to compensate for their lack of sight.  Hence, blindness appears not as an evolutionary regression but probably a shift of path forward the evolutionary line.



— written by Maria Victoria Gonzaga





1 Blindness and vision loss: MedlinePlus Medical Encyclopedia. (2019, January 1). Retrieved from


2 University of California – Davis. (2018, December 21). 300 blind mice uncover genetic causes of eye disease. ScienceDaily. Retrieved from


3 TED-Ed. (2015, January 8). YouTube. YouTube. Retrieved from


4 How does evolution explain animals losing vision? (2015, March 18). Abc.Net.Au. Retrieved from


5 Miller, S. G. (2017, March 22). Why Other Senses May Be Heightened in Blind People. Retrieved from


SELFISH GENE – selfish to persist

What is a selfish gene? A selfish gene is not a gene that makes an individual selfish. In fact, it may even be involved in the demonstration of a selfless act, a mark of altruism. Selfish gene elements (or selfish DNA) are nucleotide sequences that make copies of itself within the genome. They are regarded as unhelpful as they are of no use since they do not make a protein product. Sometimes, they may even cause harm. However, selfish genes have a vital impact on the survival of the species as a whole.




Selfish gene as a concept in evolution

Richard Dawkin coined the term selfish gene. He also proposed a gene-centric view of evolution in his book “The Selfish Gene”, which he wrote and published in 1976. An excerpt of his book states: “Genes are competing directly with their alleles for survival, since their alleles in the gene pool are rivals for their slot on the chromosomes of future generations. Any gene that behaves in such a way as to increase its own survival chances in the gene pool at the expense of its alleles will, by definition, tautologously, tend to survive. The gene is the basic unit of selfishness.” 1


Selfish gene, defined

Selfish gene - illustrated by vix maria
Selfish gene has a vital impact on the survival of the species as a whole. [Illustrator: Vix Maria]


Dawkin defined gene as a piece of chromosome that is sufficiently short to live and function long enough. A gene, he delineates, “functions as a significant unit of natural selection”.1 Based on this notion, genes tend to be selfish in a way that they would compete for their survival. They spread by forming replicas that ought to be passed on across generations. And we, as living beings, are only their vessel and an ephemeral vehicle that conveys them to the next vessel.


The genes are the immortals…. They are the replicators and we are the survival machines. When we have served our purpose we are cast aside. But genes are denizens of geological time: genes are forever. – Robert Dawkin1


Accordingly, a selfish gene would compete for its seat (loci) on the organism’s genome. Those that efficiently make copies of themselves would likely increase in number and survive in the gene pool whereas those that are less effective in the competition would tend to decrease in number.



Selfish gene and altruism

In spite of its reputation as egoistic, a selfish gene favours altruism, especially, if the act would help its replicas in other members of its species survive. Many animals – from mere ants to the more intricate humans – display altruism, which refers to a set of acts depicting a seemingly selfless behavior for the benefit or well-being of others. Hence, even if the altruistic act would eventually harm an individual, it would still prove beneficial to a selfish gene since more of its replicas in other members could wind up persisting.




Selfish gene elements

Selfish gene elements (sometimes referred to as selfish DNA) are nucleotide sequences that make copies of itself within the genome. They do not necessarily add up to the reproductive success of or confer significant advantage to the organism. Sometimes, they may even cause harm.


Recently, researchers have sequenced for the first time two selfish genes from the fungus Neurospora intermedia. A fungal spore that carries the selfish gene known as the “spore killer” would kill the sibling spores lacking the gene. 2


Another example of a selfish gene element is that found by the UCLA researchers in a strain of the roundworm Caenorhabditis elegans. They found a pair of selfish genes, one that encodes for a poison and the other that encodes for its antidote. The offspring that does not inherit the gene for the antidote dies while still an embryo because it fails to protect itself from the poison (toxin) produced by the mother. 3





These studies on selfish genes implicate that there might be many more of them and are probably just hiding in plain sight. Discovering them could one day lead to important uses. For instance, selfish genes could be used as genetic control that would deter the development of pesky parasites at the molecular level.



— written by Maria Victoria Gonzaga




1 Dawkins, R. (2016). The Selfish Gene: 40th Anniversary edition (4th ed). Oxford University Press. ISBN 0191093076.
2 Uppsala University. (2018, October 15). Unravelling the genetics of fungal fratricide. ScienceDaily. Retrieved from
3 University of California – Los Angeles Health Sciences. (2017, May 11). Study of worms reveals ‘selfish genes’ that encode a toxin, and its antidote: Discovery could suggest new ways to stop the spread of disease. ScienceDaily. Retrieved from