On the Selfish Gene
I finally got to finish Richard Dawkin’s The Selfish Gene, 30th Anniversary Edition (it was originally published in 1976) and it tells a wonderful story of evolution by focusing on the gene. Dawkins revamps my understanding of biology by proposing a gene-centric view of life. He then introduces the notion of “replicators” and “vehicles”. You can call the first self-reproducing molecules replicators, and you may also be tempted to designate the same label to living beings today. Not exactly, according to Dawkins. It is in fact the gene within living organisms that are replicators. What does that make us? We are in fact the vehicles created by a conglomerate of genes in order to propagate themselves. Dawkins himself marvels at this incredible notion:
We are survival machines – robot vehicles blindly programmed to preserve the selfish molecules known as genes. This is a truth which still fills me with astonishment.
This is an unsettling thought, but it is evidenced by nature where genes and organisms are in conflict – such as the mating behaviour of the male of some species of spiders. It also has interesting implications. Parasites that are able to transmit their genes using the same outlet as their host (e.g. through sperm and eggs) eventually fuse into their hosts and become part of the host organism. What was once a parasite becomes a symbiotic part of the host – and this could explain the evolution of eukaryotes – which conspicuously harbour mitochondria and chloroplasts of different DNA from the cell nucleus.
Our own body contains trillions of somatic cells which do not participate in producing gametes. But therein lies their role in helping the germ cells produce gametes, for without the support from somatic cells, the germ cells would perish. A tantalizing analogy given is the eusocial bee’s hive where the worker bees are sterile and only the queen produces offspring.
The “selfish” gene theory ironically explains other biological phenomena such as kin selection and altruism. Kin selection works because genes that encourage an organism to help relatives (which are likely to contain the same gene) will increase the likelihood of transmitting itself to the next generation. Since we are likely to be surrounded by kin, any gene that promotes altruism also becomes successful by the same token. Thus these “selfish” genes actually result in unselfish behaviour in organisms. Dawkins cites the Prisoner’s Dilemma, which is a well known problem in game theory, and shows us how a “nice guy” strategy, or tit for tat proves to be most advantageous in iterated games.
Let us understand what our own selfish genes are up to, because we may then at least have a chance to upset their designs, something that no other species has ever aspired to do.
There are some who may misconstrue that our “selfish” genes advocate for us to live selfishly. But this is hardly the case, as although our genes may be “selfish”, they have created wonderful vehicles that do behave with reciprocal altruism. Perhaps then, contrary to what we may think, the selfish gene has ultimately become the cooperative gene and nice guys do finish first.
Note: For an online interactive game of “Prisoner’s Dilemma” visit http://www.iterated-prisoners-dilemma.net/.
Were Mesozoic Sea Monsters Warm-Blooded?
Warm-bloodedness is the ability of an animal to maintain their body temperature at a roughly constant level, regardless of the environmental temperature. However, this term has now fallen out of favour in lieu of more specific definitions of thermoregulation.
Endothermy is the ability to regulate body temperature via internal mechanisms that generate heat such as muscle shivering or fat burning. In other words, the concept is similar to an internal “furnace”.
Homeothermy is the ability to maintain a constant internal body temperature that does not depend on the external temperature.
Tachymetabolism refers to the ability to control body temperature by having a high resting metabolism.
The reason why there are 3 definitions for warm-bloodedness is because scientists have discovered that not all traditionally warm-blooded animals (mammals and birds) fit into all categories. On the flipside, some “cold-blooded” animals such as the bluefin tuna and mackerel shark display some features of “warm-bloodedness”
In the Mesozoic era, while the dinosaurs conquered the land, 3 general groups of fascinating reptiles ruled the seas; the dolphin-like ichthyosaurs, the long-necked plesiosaurs and the serpentine mosasaurs. A study in the June 11th issue of Science suggests that these top-tier sea creatures could have displayed some features of warm-bloodedness. How did they arrive at this tantalizing conclusion?
Well, warm-bloodedness leaves clues even in the fossils of long dead animals. The ratio of various isotopes of oxygen are preserved in the phosphate minerals of tooth enamel. Isotope geochemist Christopher Lecuyer then compared the proportion of oxygen-18 isotope in the tooth enamels of ichthyosaurs, plesiosaurs and mosasaurs to those of the presumably cold-blooded fish in the same geologic strata.
What they found was that the marine reptiles had a higher proportion of oxygen-18 compared to the cold-blooded fish. This suggests that they had some degree of warm-bloodedness. The researchers concluded that ichthyosaurs and plesiosaurs had body temperatures of about 35-39 degrees Celcius, which is a whopping 20 degrees warmer than the sea temperature. Like tuna and swordfish, which are homeothermic and endothermic, ichthyosaurs and plesiosaurs could have generated heat from the muscles in their body.
Elasmosaurus, a plesiosaur, and one of my favourite prehistoric creatures.
Tylosaurus, a mosasaur, chomps down on a meal in the Late Cretaceous.
A school of Shonisaurus, the largest ichthyosaur discovered, roam the late Triassic seas
The marine sea reptiles were a huge evolutionary success, dominating the mesozoic seas. Warm-bloodedness may have played a key role to the success of ichthyosaurs and plesiosaurs because studies of body plans have suggested that these creatures were pursuit predators that needed to stay active to hunt. The evidence for mosasaurs is more equivocal but still enough to conclude that they had some degree of temperature control. This could be explained by the idea that mosasaurs were ambush predators that required less energy. Nevertheless, this study gives us enticing proof of how warm-bloodedness evolved in these majestic aquatic reptiles from their cold-blooded land cousins
How Endogenous Retroviruses Predict Evolution by Common Descent
I highly recommend the Facts of Evolution Series on Youtube. In this latest installment, the author talks about retroviruses. These are viruses that reverse transcribe RNA into DNA (which is the opposite of what most organisms do). Examples of such retroviruses are the HTLV-1 virus which causes leukemia and the HIV virus which causes AIDS. However, some retroviruses can insert their DNA into host germ cells where they are inherited by descendants of the host. These are called endogenous retroviruses (ERV), and they persist in the genome of the species that becomes infected.
Under the idea of common descent, we can predict the evolutionary relationships of different species by comparing their genomes and identifying ERVs. If the ancestor of humans have acquired ERV1 after the split from other apes, we can expect to find ERV1 in the genome of all humans but not in the genome of any other ape. With the advance of genetics, scientists are comparing ERVs between species and so far everything has added up, thus providing another strong evidence for evolution.
Interestingly, where mammals except monotremes are concerned, ERVs are known for role in allowing pregnancy to occur. During pregnancy, some ERVs are turned on and they cause an immunosuppressive effect to protect the embryo from the maternal immune system. It is thought that at some point a retrovirus infected an early mammalian ancestor, and this enabled the evolution of vivaparity as the fetus became more resistant to the mother’s immune system. They also play a role in the formation of the placental syncytium, via viral fusion proteins. An example of a viral fusion protein in retroviruses we see today is gp41 seen in HIV.
A Slew of New Ceratopsians
I just found out that the past week has been a busy busy week for ceratopsian discoveries. Ceratopsians are among the last wave of magnificent herbivorous dinosaur groups to emerge in the late Cretaceous.
This is Coahuilaceratops magnacuerna (Koh-WHE-lah-SARA-tops mag-NAH-KWER-na) which is the first horned dinosaur unearthed in Mexico. Its latin name means “great horned face from Coahuila”. The most unique feature of this species which lived 72 mya is that it had horns up to 4 feet long, which is longer than any other ceratopsian.
The 1 metre long Ajkaceratops kozmai is small in stature but it represents the first ceratopsian discovery in Europe. In the late Cretaceous, Europe was an isolated island landmass and this find is evidence of island dwarfism and the migration of ceratopsians from Asia. This ceratopsian is probably a protoceratopsid related to Magnirostris.
Sinoceratops zhuchengensis is another important discovery because before this ceratopsids have been exclusively found in North America. This late Cretaceous dinosaur also blurs the distinction between 2 subfamilies of ceratopsids, the chasmosaurines and the centrosaurines.
This fearsome looking creature from southern Utah is appropriately named Diabloceratops eatoni (Latin for devil horned face). At 80 million years old, it is also one of the oldest ceratopsids. Has to be one of the coolest frill horns in the dinosauria.
Last but not least is this stunning specimen from the Montana-Alberta border. Christened Medusaceratops lokii for its curved, snakelike frill-horns which resembled the head of Medusa, as well as its arching brow horns which are reminiscent of the Norse God Loki, this beast lived 78 million years ago and grew up to 20 feet long.
Should Medical Students Study Evolution?
It was Russian Orthodox Christian and evolutionary biologist Theodosius Dobzhansky who famously said in 1973 that “Nothing in biology makes sense except in the light of evolution”. Today, evolution is undeniably the keystone of almost every biological science. It is therefore shocking to know that one vital field seems to have been left behind. Where in the science of medicine is evolution?
To those uninitiated with evolution, the human body is often regarded as a perfect creation. Why then, do we get sick? Why for example, do we get heart attacks? When I read about a disease in a medical textbook I expect to find the following:
1. The signs and symptoms of the disease
2. The etiology or pathophysiology of the disease
3. Diagnostic criteria
4. Management
Hence, medical science tells us how heart attacks happen and which kinds of people are most at risk. But does medicine tell us why human beings get heart attacks at all? How can it be that this most basic of questions goes not only unanswered by medicine, but largely ignored?
In 1994, “Why We Get Sick”, a groundbreaking book by Randolph Nesse and George C. Williams ushered in public awareness of evolutionary medicine. To put it simply, it is the application of the principles of evolutionary theory to understand health and disease.
We are already familiar with the concept of antibiotic resistance but current medical education seems to downplay the role of evolution by scarcely mentioning it. Humans and pathogens engage in an evolutionary arms race that can be succinctly explained with a quote from Lewis Carrol’s novel “Through the Looking Glass”. In it the Red Queen says:
“It takes all the running you can do, to keep in the same place”
Hence humans and pathogens are waging an arms race, with each side making small improvements via natural selection in order to maintain its biological fitness. This is known as the “Red Queen hypothesis“. The question posed by the book is this : Could human conditions and sickness be explained by evolutionary principles?
Firstly, human beings are susceptible to some kinds of diseases via our genetic makeup. You may ask why would a defective gene that causes a disease such as sickle cell anemia continue to persist? Shouldn’t natural selection have eliminated it? Unfortunately this isn’t the case because genes don’t care about how happy or healthy we are, it has no purpose but to make sure it gets transmitted to the next generation. Anything that increases the chance of a gene being passed on will be present in future generations. Scientists have discovered that although homozygotes with both copies of the defective sickle cell gene develop sickle cell anemia, heterozygotes with one copy of the defective gene have an increased resilience to malaria.
Sometimes a gene that causes disease has no disadvantage in reproductive output, some have hidden advantages while others still are quirks that only present with disease in a novel environment. Why does a deadly neurodegenerative disease such as Huntington’s disease occur? Because it typically has a late onset in life, whether a person has Huntington’s doesn’t affect how many children he or she will have, and the gene that causes Huntington’s will continue to propagate for generations.
It is also important to understand the environment in which humans evolved in the first place – the African savannah. Imagine now the environment we live in today. We sit on our butts most of the day and load ourselves with a diet rich in “nutrients” that use to be much rarer : salt, sugar and fat. Could it be that “modern” diseases such as lower back pain and heart attacks are actually a result of our bodies having not enough time to evolve and adapt to a new and novel environment?
The budding field of Darwinian medicine can have huge consequences on how we understand disease and how patients are treated. Yet evolution is curiously absent from the medical curriculum. What do we do with the evolutionary hypotheses proposed on disease? We need them to be scientifically tested and thus more research needs to be done in a field that could revolutionize medicine as we know it. Only then can we make sense of why we get sick.
I highly recommend Nesse and Williams’ “Why We Get Sick : The New Science of Darwinian Medicine”, although it is a little old.
http://www.amazon.com/Why-We-Get-Sick-Darwinian/dp/0679746749
Web Resources on evolutionary medicine
1. http://www-personal.umich.edu/~nesse/ – Randolph Nesse’s website
2. http://en.wikipedia.org/wiki/Evolutionary_medicine
On the descent of man
During the past 2 weeks of my holidays I’ve been occupying myself with pc games and catching up on the TV shows I like.
But I’ve also been continuing my reading on evolution which has brought me to this nice cream coloured book I found in Borders last November but haven’t had the time to read since.
The Descent of Man And Selection in Relation to Sex, The Concise Edition
In contrast to my copy of The Origin of Species which I found difficult to read over 5 years ago, I very much preferred reading the concise edition of The Descent of Man (1871). This is because the notoriously longwinded chapters of Victorian English have been trimmed down into bite sized chunks. Neatly inserted between these chunks are slices of additional commentary by science writer Carl Zimmer which give Darwin’s notions a modern update.
Astoundingly, it is these updates which show that although Darwin had little knowledge of modern genetics at the time, the foundations of his ideas on human evolution largely hold true even to this day.
The Descent of Man is widely regarded as a classic work of science because it is in this book that Darwin finally addresses the elephant in the room – where did we come from? Interestingly the more well-known Origins of Species is bereft of any clue to human evolution save for a brief and vague mention that ” light will be thrown on the origins of man and his history”. Moreover it took more than a decade for Darwin to publish Descent after Origins, during which he took a detour on orchids and variation under domestication. Why the long break?
According to primatologist Frans de Waal who writes the foreword to this concise edition of Descent, Darwin had said that he wanted to keep his own musings about human evolution to himself. He judged that his ideas would be far too revolutionary and radical for the general public and publishing them would only serve to create a stronger opposition to his already controversial theory of evolution.
What is so radical about the Descent of Man? Well for starters Darwin compares the anatomy of human beings and animals and reveals that the anatomical differences lie not on discrete dichotomies but instead on a single continuum. He points out that the peculiar anatomical anomalities called vestigial “organs” in humans which no longer serve their intended or original purpose (it is actually inaccurate to think of vestigial organs as serving NO purpose at all) are relics which link us to our cousins in the animal kingdom.
Darwin consistently mentions that the differences we share with animals are a matter of “degree and not kind”. This is a stark contrast to the views of his contemporaries such as Alfred Wallace who argued that humans were a species of ape, physically, but our intelligence could not have evolved and is a sign of divine intervention.
Darwin addresses this point by then comparing human and animal behaviour. He makes the case that humans and animals aren’t so different after all, that the social instincts that form the glue between animal interactions such as loyalty and altruism in nature actually form the basis of the evolution of human morality.
This was a HUGE deal because many people at the time (and even today) thought that if humans believed they were merely “animals” both physically AND mentally, there was nothing to stop them from “moral decay” or “acting like animals”. Darwin himself however rejected the view that morality was given by God and instead proposed that morality evolved in humans beings because it was important for our very survival. To quote Darwin himself,
It is obvious, that the members of the same tribe would approve of conduct which appeared to them
to be for the general good, and would reprobate that which appeared evil.
To do good unto others–to do unto others as ye would they should do unto
you–is the foundation-stone of morality.
The Descent of Man is a gem of a book because by comparing the physical structures and mental abilities of humans and other animals such as primates, Darwin predicted our origins from ape-like creatures before the first of them was excavated in Africa, before there was any knowledge of DNA and amidst intense opposition from the public. That is why it is a cultural and scientific milestone published well ahead of its time. I recommend it to all readers who have an interest in evolution.
Ken.
Leokl
The Philosophical Platypus 