Arxiu d'etiquetes: natural selection

From lab to big screen (II)

As I told you in the previous article on genetics and cinema, there is a wide variety of films that talk about genetics. In the next article we will talk about science fiction, with two well-known films. Beware: spoilers!

GATTACA (1997)

Director: Andrew Niccol

Cast: Ethan Hawke, Uma Thurman, Jude Law

Genre: Science fiction

Story line: Vincent is one of the last “natural” babies born into a sterile, genetically-enhanced world, where life expectancy and disease likelihood are ascertained at birth. Myopic and due to die at 30, he has no chance of a career in a society that now discriminates against your genes, instead of your gender, race or religion. Going underground, he assumes the identity of Jerome, crippled in an accident, and achieves prominence in the Gattaca Corporation, where he is selected for his lifelong desire: a manned mission to Saturn’s 14th moon (titan). Constantly passing gene tests by diligently using samples of Jerome’s hair, skin, blood and urine, his now-perfect world is thrown into increasing desperation, his dream within reach, when the mission director is killed – and he carelessly loses an eyelash at the scene! Certain that they know the murderer’s ID, but unable to track down the former Vincent, the police start to close in, with extra searches, and new gene tests. With the once-in-a-lifetime launch only days away, Vincent must avoid arousing suspicion, while passing the tests, evading the police, and not knowing whom he can trust.

Relation with genetics: GATTACA is the “genetic” film par excellence. Starting with the title, this is formed by the initials of the four nitrogenous bases that make up DNA (guanine, adenine, thymine and cytosine). In addition, the helical shape of the DNA is repeated in several moments of the film, as in the stairs of Vincent’s house.

The main issue is about genetic selection, all children born have been genetically selected, closely linked to bioethics. The idea of ​​this selection is to reach eugenics, that is, to improve the population by selecting the “best” humans. This concept can be related to the Hitler’s Germany, who believed that Germans belonged to a superior group of races called “Aryan”. Hitler said that German Aryan race had been better endowed than the others and that this biological superiority destined Germans to oversee an empire in Eastern Europe.

Although nowadays genetic selection is valid and is used to avoid diseases, it is not applied with the same purposes as those of the film. At present, it is decided to carry out genetic selection after having studied the family and carried out the appropriate genetic counselling. It aims to help patients and their families avoid the pain and suffering caused by a genetic disease and should not be confused with the eugenic objective of reducing the incidence of genetic diseases or the frequency of alleles considered to be deleterious in the population.

This is very related to the genetic discrimination, case also exposed in the film. Gattaca is situated in a possible future in which genetics, trying to improve the quality of life of society, causes a movement of discrimination.

When we talk about discrimination, we tend to think about racial discrimination. This is defined as the different or exclusive treatment of a person for reasons of racial or ethnic origin, which constitutes a violation of the fundamental rights of individuals, as well as an attack on their dignity. Racism has been present throughout the history of mankind, especially in the twentieth century with racial discrimination in the United States and apartheid in South Africa.

For some time now, genetic discrimination has been gaining weight. It happens when people are treated differently by their company or insurance company because they have a genetic mutation that causes or increases the risk of a hereditary disorder. Fear of discrimination is a common concern among people who undergo genetic testing, and is a current problem that concerns the population because your own genome does not have to be a curriculum vitae that opens or closes doors as happens in the film. Vincent goes to work in Gattaca after performing a urine test and a blood test, since in Gattaca they do not choose workers for their ability or ability but for their DNA.

However, the film ends with the sentence “There is no gene for the human spirit”. This means that, although the society in which Gattaca is located is based on genetic modification, it does not affect the morality and final character of people because there is no way to genetically relate to the spirit, only the body has the genetic information.

Video 1. Trailer Gattaca (Source: YouTube)


Director: Steven Spielberg

Cast: Sam Neill, Laura Dern, Jeff Goldblum

Genre: Science fiction

Story line: Huge advancements in scientific technology have enabled a mogul to create an island full of living dinosaurs. John Hammond has invited four individuals, along with his two grandchildren, to join him at Jurassic Park. But will everything go according to plan? A park employee attempts to steal dinosaur embryos, critical security systems are shut down and it now becomes a race for survival with dinosaurs roaming freely over the island.

Relation with genetics: In the first film of this saga, from dinosaur’s fossils scientists extract DNA to be able to clone dinosaurs. The cloned dinosaurs will be part of the Jurassic park on which the film is based.

It is true that DNA can be extracted from bones, widely used in forensic genetics. Same as the issue of cloning, which was known by the Dolly sheep, the first large animal cloned from an adult cell in July 1996. But the film goes further and raises the possibility of reintroducing, in today’s world, extinct species and challenge natural selection.

Video 2. Trailer Jurassic Park (Source: YouTube)




Check the evolution in your own body

42% of the US population and 11.5% of the Spanish people do not believe in evolution. However, there are different evidence that Darwin was right, some of them in your own body. Have you had your appendix or wisdom teeth removed? Find out in this post which vestigial organs you have inherited from your ancestors.


Vestigial structures (often called organs althouth they are not organs properly) are body parts that have been reduced or have lost its original function during the evolution of a species. They can be found in many animals, including humans.

Esqueleto de orca en el que se observan vestigios de las extremidades traseras. Foto: Patrick Gries
Orca skeleton in which vestiges of the hind limbs can be seen. This is a proof of its terrestrial origins. Photo: Patrick Gries

Vestigial structures were fully functional in the ancestors of these species (and in the homologous structures of other existing species), but currently its function is practically useless or it has changed. For example, the second pair of flying wings in some insects such as flies have lost their function and they have been reduced to balance organs (halteres). If you want to know more about the evolution of flight in insects click here.

Besides physical structures, vestigial features can also manifest itself in behavior or biochemistry processes.


Natural selection acts on species favoring features that increase their survival and eliminating the ones with no benefits, for example when changes appear in the habitat. Individuals with unfavorable characteristics will die or will breed less and that feature will be removed after some generations, while favorable traits will remain as their carriers can pass them to the next generation.

Sometimes there are features that are neither favorable nor unfavorable, so they continue appearing in the next generations. But all has a cost structure (energy, risk to become infected, develop tumors…), so selective pressure continues acting to eliminate something that is not conducive to the success of the species. This is the case of vestigial structures, which “take longer” disappear throughout evolution. Their existence reveal that in the past these structures had an important role in our ancestors.



We talked about it in How animals see the world. The third eyelid is a transparent or translucent membrane that protects and moisten the eye without losing visibility. It is common in amphibians, reptiles and birds. Among primates, it is only functional in lemurs and lorises.

membrana nictitante, nictitating membrane
Nictitating membrane or third eyelid of a masked lapwing (Vanellus miles). Photo: Toby Hudson

In humans the plica semilunaris is a remnant of the nictitating membrane. Obviously we can not move it but still has some lacrimal drainage function and helps on the eye movement (Dartt, 2006).

Plica semilunaris (pliegue semilunar). Foto: desconocido
Plica semilunaris. Photo: unknown


10% of the population has a thickening in the ear, a vestige of the common pointy ear in primates. This structure is called Darwin’s tubercle and has no function.

Variabilidad del Tubérculo de Darwin en la punta de la oreja (0= ausente). Puede presentarse en otras zonas del pabellón auditivo: ver publicación.
Variability of Darwin’s tubercle at the top of the ear (0 = absent).  Credit.
Comparación entre la oreja de un macaco y la nuestra. Fuente
Comparison between the ear of a yellow baboon (Papio cynocephalus) and ours. Credit

Also, primates (and other mammals) have mobile ears to lead the pinna toward the sound source: surely you have noticed it in your house dog or house cat. Humans (and chimps) no longer have that great mobility, although some people may move slightly pinna. It has been proven with electrodes these muscles are excited when we perceive a sound that comes from a particular direction (2002).

Auricular muscles responsible of movement of the pinna. Credit

The occipitofrontalis muscle has lost its function to prevent the head from falling, but participates in facial expression.


16% of Caucasians do not have this muscle on the wrist, neither 31% of nigerian people neither 4,6% of chinese people. It can even appear in one arm and not in the other or be double.

It is believed that this muscle actively participated in the arboreal locomotion of our ancestors, but currently has no function, because it does not provide more grip strength. This muscle is longer in completely arboreal primates (like lemurs) and shorter in land primates, like gorillas (reference).

And do you have it or not? Try it: join your thumb and pinky and raise your hand slightly.

mireia querol, mireia querol rovira, palmaris longus, musculo palmar largo, tendon
I have two palmaris longus in the left arm and one on the right. Photo: Mireia Querol


35% of people do not have wisdom teeth or third molar. In the rest, its appearance is usually painful and removal is necessary.

Yo no tengo el tercer molar. Foto: Mireia Querol Rovira
I don’t have the third molar. Photo: Mireia Querol Rovira

Our hominin ancestors had them, much bigger than ours. A recent research explains that when a tooth develops, emits signals that determine the size of the neighboring teeth. Reducing the mandible dentition and the other along evolution has resulted in reduced molars (and eventually the disappearance of the third).

Comparativa entre la dentición de un chimpancé, Australopithecus afarensis y Homo sapiens. Fuente
Comparison between the dentition of a chimpanzee, Australopithecus afarensis and Homo sapiens. Look at the reduction of the last three molars between afarensis and sapiens, Credit


If you touch your spine till the end, you will reach the coccyx or tailbone. It is three to five fused vertebrae, vestige of the tail of our primate ancestors. In fact, when we were in the womb, in the early stages of embryo development a 10-12 tail vertebrae formation is observed.

Distintos estados en el desarrollo embrionmario humano y comparación con otras especies. Créditos en la imagen
Different stages in human embryonic development (1 to 8) and comparison with other species. Credits in the image.

Subsequently it is reabsorbed, but not in all cases: it has been reported 40 newborns with a tail.

Neonato nacido con cola. Una mutación ha evitado la inhibición del crecimiento de la cola durante la gestación. Fuente
Infant born with tail. A mutation has prevented the growth inhibition of the tail during pregnancy. Credit

Although we have no tail, currently these bones serve as anchors of some pelvic muscles.

mireia querol, mireia querol rovira, coxis, sacro, sacrum, tailbone, rabadilla
Tailbone position. Photo: Mireia Querol Rovira


It is estimated that up to 5% of the world population has more than two nipples. These “extra” nipples can be presented in different ways so sometimes are confused with freckles or moles. They are located in the mammillary line (from the axilla to the groin), exactly in the same position as other mammals with more than two breasts (observe your house dog, for example). Usually the number of breasts corresponds to the average of offspring that has a mammal, so extra nipples would be a vestige from when our ancestors had more offspring per birth. Usual is 3 nipples, but has been documented a case of up to 8 nipples in a person.

Pezón suplementario debajo del principal. Fuente
Additional nipple below the main one. Credit



Surely you’ve experienced that if you bring anything into the hands of a baby, automatically he grabs it with such a force that would be able to hold his own weight. This reflex disappears at 3-4 months of age and is a remnant of our arboreal past and the way to grab the hair of the mother, as with the other current primates. Watch the next video in 1934 on a study of twins (minute 0:34):

On the feet there is also a reflex of trying to grab something when the foot of a baby is touched. It disappears at 9 months of age.

By the way, have you noticed how easily children climb on any handrails or higher zones in a playground?


Cold, stress or intense emotion (eg, listening to some music) causes the piloerector muscle to raise the hair giving the skin the appearance of a plucked chicken. It is an involuntary reflex in which some hormones, like adrenaline (which is released in the mentioned situations) are involved. What utility had this to our ancestors and has in modern mammals?

  • Increasing the space between the skin and the external surface, so that hot air trapped between hair helps on maintaining temperature.
  • Looking bigger to scare off potential predators or competitors.
Chimpancé con el pelo erizado durante un display antes de un conflicto. Foto: Chimpanzee Sanctuary Northwest
Chimpanzee with hair bristling in a display before a conflict. Photo: Chimpanzee Sanctuary Northwest

Obviously we have lost hair in most parts of the body, so although we retain the reflex, it has no use to us or to keep warm or to ward off predators. The hair has been preserved abundantly in areas where protection is necessary or due to sexual selection (head, eyebrows, eyelashes, beard, pubis…), but in general, can also be considered a vestigial structure.

There are more vestigial structures but in this post we have focused on the most observable. In future posts we will discuss other internal structures, like the famous appendix or vomeronasal organ.


Evolution for beginners 2: coevolution

After the success of Evolution for beginners, today we’ll continue  knowing the basics of biological evolution. Why  exist insects that seem orchids and vice versa? Why gazelles and cheetahs are almost equally fast? Why your dog understands you? In other words, what is coevolution?


We know that it is inevitable that living beings establish symbiotic relationships between them. Some depend on others to survive, and at the same time, on elements of their environtment as water, light or air. These mutual pressures between species make that evolve together, and as one evolve as a species, in turn it forces the other to evolve. Let’s see some examples:


The most known process of coevolution is pollination. It was actually the first co-evolutionary study (1859) by Darwin, although he didn’t use that term. The first to use the word coevolution were Ehrlich and Raven (1964).

Insects existed long before the appearance of flowering plants, but their success was due to the discovery that nectar is a good reserve of energy. In turn, the plants found in the insects another way more effectively to carry pollen to another flower. Pollination by the wind (anemophily) requires more production of pollen and a good dose of luck to at least fertilize some flowers of the same species. Many plants have developed flowers that trap insects until they are covered with pollen and then set them free. These insects have hairs in their body to enable this process. In turn some animals have developed long appendages (beaks of hummingbirds, butterflies’ proboscis…) to access the nectar.

Polilla de Darwin (Xantophan morganii praedicta). Foto de Minden Pictures/Superstock
Darwin’s moth (Xantophan morganii praedicta). Photo by Minden Pictures/Superstock

It is the famous case of the Darwin’s moth (Xanthopan morganii praedicta) of which we have already talked about. Charles Darwin, studying orchid Christmas (Angraecum sesquipedale) saw that the nectar was 29 cm inside the flower. He sensed that there should exist an animal with a proboscis of this size. Eleven years later, Alfred Russell Wallace reported him that the Morgan’s sphinxs had proboscis over 20 cm long, and a time later they were found in the same area where Darwin had studied that species of orchid (Madagascar). In honor of both it was added “praedicta” to the scientific name.

There are also bee orchids that mimic female insects to ensure their pollination. To learn more about these orchids and the Christmas one, do not miss this post by Adriel.

Anoura fistulata, murcielago, bat
The bat Anoura fistulata and its long tongue. Photo by Nathan Muchhala

But many plants not only depend on insects, also some birds (like humming birds) and mammals (such as bats) are essential to pollination. The record for the longest mammal tongue in the world is for a bat from Ecuador (Anoura fistulata); its tongue measures 8 cm (150% of the length of its body). It is the only who pollinates one plant called Centropogon nigricans, despite the existence of other species of bats in the same habitat of the plant. This raises the question of whether evolution is well defined, and occurs between pairs of species or it is diffuse due to the interaction of multiple species.


The cheetah (Acinonyx jubatus) is the fastest vertebrate on land (up to 115 km/h). Thomson’s gazelle (Eudorcas thomsonii), the second (up to 80 km/h). Cheetahs have to be fast enough to catch a gazelle (but not all, at risk of disappearing themselves) and gazelles fast enough to escape almost once and reproduce. The fastest gaelles survive, so nature selects in turn faster cheetahs, which are who eat to survive. The pressure from predators is an important factor that determines the survival of a population and what strategies should follow the population to survive. Also, the predators will find solutions to possible new ways of life of their prey to succeed.

Guepardo persiguiendo una gacela. Foto de Federico Veronesi
Cheetah hunting a Thomson’s gazelle in Kenya. Photo by Federico Veronesi

The same applies to other predator-prey relationships, parasite-host relationships, plants-herbivores, improving their speed or other survival strategies like poison, spikes…


Our relationship with dogs since prehistoric times, it is also a case of coevolution. This allows, for example, to create bonds with just looking at them. If you want more information, we invite you to read this post where we talk about the issue of the evolution of dogs and humans in depth.

Another example is the relationship we have established with the bacteria in our digestive system, essential for our survival. Or with pathogens: they have co-evolved with our antibiotics, so using them indiscriminately has favored these species of bacteria to develop resistance to antibiotics.


Coevolution is one of the main processes responsible for the great biodiversity of the Earth. According to Thompson, is responsible for the millions of species that exist instead of thousands.

The interactions that have been developed with coevolution are important for the conservation of species. In cases where evolution has been very close between two species, if one become extint will lead to the extinction of the other almost certainly. Humans constantly alter ecosystems and therefore biodiversity and evolution of species. Just declining one species, we are affecting many more. This is the case of the sea otter (Enhydra lutris), which feeds on sea urchins.

Nutria marina (Enhydra lutris) comiendo erizos. Foto de Vancouver Aquarium
Sea otter (Enhydra lutris) eating sea urchins. Photo by Vancouver Aquarium

Being hunted for their fur, urchins increased number, devastated entire populations of algae (consumer of CO2, one of the responsible of global warming), seals who found refuge in the algae nonexistent now were more hunted by killer whales… the sea otter is therefore a key species for the balance of this ecosystem and the planet, as it has evolved along with urchins and algae.

Coevolutive relations between flowers and animals depend on the pollination of thousands of species, including many of agricultural interest, so we must not lose sight of the seriousness of the issue of the disappearance of a large number of bees and other insects in recent years. A complex case of coevolution that directly affects us is the reproduction of fig.


As we have seen, coevolution is the evolutionary change through natural selection between two or more species that interact reciprocally.

It is needed:

  • Specificity: the evolution of each feature of a species is due  to selective pressures of the feature of the other species.
  • Reciprocity: features evolve together.
  • Simultaneity: features evolve simultaneously.



Evolution for beginners

Biological evolution is still not well understood by general public, and when we speak of it in our language abound expressions that confuse even more how mechanisms that lead to species diversity work. Through questions you may have ever asked yourself, in this article we will have a first look at the basic principles of evolution and debunk misconceptions about it.


Outside the scientific field, the word “theory” is used to refer to events that have not been tested or assumptions. But a scientific theory is the explanation of a phenomenon supported by evidence resulting from the application of the scientific method.

scientific method
The scientific method. Image by Margreet de Heer.

Theories can be modified, improved or revised if new data don’t continue to support the theory, but they are always based on some data, repeatable and verifiable experiments by any researcher to be considered valid.

So few people (sic) doubts about the heliocentric theory (the Earth rotates around the Sun), or the gravitational theory of Newton, but in the popular imagination some people believe that the theory of evolution made by Charles Darwin (and Alfred Russell Wallace) is simply a hypothesis and has no evidence to support it. With new scientific advances, his theory has been improved and detailed, but more than 150 years later, nobody has been able to prove it wrong, just the contrary.


We have many evidences and in this post we will not delve into them. Some of the evidence available to us are:

  • Paleontological record: the study of fossils tell us about the similarities and differences of existing species with others thousands or millions old, and to establish relationships respect each other.
  • Comparative anatomy: comparison of certain structures that are very similar between different organisms, can establish whether they have a common ancestor (homologous structures, for example, five fingers in some vertebrates) if they have developed similar adaptations (analogous structures, for example, the wings of birds and insects), or if they have lost their function (vestigial organs, such as the appendix).
Homologous organs in humans, cats, whales and bats
Homologous organs in humans, cats, whales and bats
  • Embryology: the study of embryos of related groups shows a strong resemblance in the earliest stages of development.
  • Biogeography: The study of the geographical distribution of living beings reveals that species generally inhabit the same regions as their ancestors, although there are other regions with similar climates.
  • Biochemistry and genetics: chemical similarities and differences allow to establish relationships among different species. For example, species closely related to each other have a structure of their DNA more similar than others more distant. All living beings share a portion of DNA that is part of your “instructions”, so there are also found in a fly, a plant or a bacterium, proof that all living things have a common ancestor.


Both expressions, frequently used, mean that living beings have an active role to adapt to the environment or “someone” has designed them to live exactly where they are. It is a typical example of Lamarck and giraffes: as a result of stretching the neck to reach the higher leaves of the treescurrently giraffes have this neck for giving it this use. They have a necessity, they change their bodies to success. It is precisely upside down: it is the habitat that selects the fittest, nature “selects” those that are most effective to survive, and therefore reproduce. It is what is known as natural selection, one of the main mechanisms of evolution. It needs three requirements to act:

  • Phenotypic variability: there must be differences between individuals. Some giraffes necks were slightly longer than others, just as there are taller people than others, with blue or brown eyes.
  • Biological fitness: this difference has to suppose an advantage. For example, giraffes with a slightly longer neck could survive and reproduce, while the others don’t.
  • Heredity: these characters must be transmitted to the next generation, the offspring will be slightly different to that feature, while “short neck” feature transmits less and less.
natural selection
The variability in the population causes individuals with favorable characteristics to reproduce more and pass on their genes to the next generation, increasing the proportion of those genes. Image taken from Understanding evolution

Over the years these changes are accumulated until the genetic differences are so big that some populations may not mate with others: a new species has appeared.

If you thought that this is similar to artificial selection that we do with the different breeds of dogs, cows who give more milk, trees bearing more fruit and larger, congratulations, you think like Darwin as it was inspired by some of these facts. Therefore, living beings are mere spectators of the evolutionary process, depending of changes in their habitat and their genetic material.


Genetic variability allows natural selection act. Changes in the genetic material (usually DNA) are caused by:

  • Mutations: changes in the genome that may be adverse or lethal for survival, indifferent or beneficial to survival and reproduction. If they have benefits, they will pass to the next generations.
  • Gene flow: is the motion of genes between populations (migration of individuals allows this exchange when mate with others in a different population).
  • Sexual reproduction: allows recombination of genetic material of different individuals, giving rise to new combinations of DNA.

Populations that have more genetic variability are more likely to survive if happen any changes in their habitat. Populations with less variability (eg, being geographically isolated) are more sensitive to any changes in their habitat, which may cause their extinction.

Evolution can be observed in beings with a very high reproduction rate, for example bacteria, since mutations accumulate more quickly. Have you ever heard that bacteria become resistant to our antibiotics or some insects to pesticides? They evolve so quickly that within a few years were selected the fittest to survive our antibiotics.


Theory of Evolution has various consequences, such as the existence of a common ancestor and that therefore, that we are animals. Even today, and even among the young ones, there is the idea that we are something different between living beings and we are in a special podium in the collective imagination. This anthropocentric thinking caused Darwin mockery and confrontations over 150 years ago.

caricatura, darwin, mono, orangutan
Caricature of Darwin as an orangutan. Public domain image first published in 1871

We use our language to be “more evolved” as a synonym for more complex, and we consider ourselves one species that has reached a high level of understanding of their environment, so many people believe that evolution has come to an end with us.

The question has a mistake of formulation: actually evolving pursues no end, it just happens, and the fact that millions of years allows the emergence of complex structures, it does not mean that simpler lifeforms are not perfectly matched in the habitat where they are. Bacteria, algae, sharks, crocodiles, etc., have remained very similar over millions of years. Evolution is a process that started acting when life first appeared and continues to act in all organisms, including us, although we have changed the way in which natural selection works  (medical and technological breakthroughs, etc.).


The truth is that we don’t come from monkeys, we are monkeys, or to be more rigorous, apes. We have not evolved from any existing primate. As we saw in a previous post, humans and other primates share a common ancestor and natural selection has been acting differently in each of us. That is, evolution has to be viewed as a tree, and not as a straight line, where each branch would be a species .

darwin, árbol, evolución, darwin tree, arbre evolutiu
First scheme of the evolutionary tree of Darwin in his notebook (1837). Public domain image.

Some branches stop growing (species become extinct), while others continue to diversify. The same applies to other species, in case you have asked yourself, “if amphibians come from fish, why are there still fish?”. Currently, genetic analyzes have contributed so much data that they make so difficult to redesign the classical Dariwn’s tree.

árbol filogenético, clasificación seres vivos, árbol de la vida
Classification of live organisms based on the three domains Archaea, Bacteria and Eukarya, data of Carl R. Woese (1990). Included in Eukarya there are the Protista, Fungi, Plantae and Animalia kingdoms. Image by Rita Daniela Fernández.

Evolution is a very broad topic that still generates doubts and controversies. In this article we have tried to bring to uninitiated people some basics, where we can delve into the future. Do you have any questions about evolution? Are you interested into a subject that we have not talked about? You can leave your comments below.