Limits of Darwin theory?

The question of how Darwinism explains the *diminishment* of features like senses that were once useful, without an obvious disadvantage, is a valid question. (ericnutsch's answer is very good.)

There are two things to remember:

- First, sense organs can't be separated from the brain. Hearing is not just a property of ears, but ears+auditory parts of the brain.

- Second, genetics can't be separated from embryology. It's during the development of the embryo that genetics gets expressed. So embryological resources dedicated to building organs that are not used (or under used) by the brain, are a liability.

The classic example are the blind cave fish. After evolution within a dark cave they have vestigial, but useless eyes. Even if you take unhatched eggs and raise them in an environment with light, they are still blind ... which shows that the blindness is not just a factor of being born with good eyes that just never develop in a dark environment, but has been incorporated into the genes of the fish. Why? If the genes for eyes were harmless, why would evolution get rid of them? Because apparently such genes are a liability. Eyes use energy, even if there is no light to see. Parts of the nervous system get dedicated to receiving visual information that would be better redirected elsewhere. For these reasons, a fish whose embryological programming still produces functioning eyes in a lightless environment, is at a slight *disadvantage* to other species-mates without that programming. So blindness *is* an advantage in a consistently lightless world. So after many generations, the fish become more and more permanently (congenitally) blind.

In the case of hearing in primates, remember that hearing has to do with the parts of the brain dedicated to processing sound information. In the case of humans, it's not just that they lost the need for the type of sound sensitivity that our primate cousins still have, but rather that hearing became dedicated to a completely different *type* and range of sound information ... the sound of the human voice!

Human language is considered to be one of the driving forces behind the huge growth of the brain and intelligence. The brain areas dedicated to processing and creating language, as well as the abstract concepts they enabled, just grew. But this would also come at the expense of nervous-system resources used for other tasks, like sensitive hearing. In fact, over-sensitive hearing would become a liability in an environment of grunting and babbling species-mates.

The loss of smell would have a similar Darwinian explanation. Those areas of the brain dedicated to processing delicate smells just became an unnecessary liability ... those areas were best adapted for other functions. (Even the physical space taken up in the skull by large nasal passages, may have shrunk in response to the enlarging brain.) And once the brain capacity for processing subtle smell information is lost, the embryological resources dedicated to building a sensitive nose, become a liability.

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ejc below offers an alternative explanation that I failed to consider. I.e. just because our cousin species have good hearing and smell doesn't mean that our common *ancestor* did. It may just be that they developed good hearing and smell and we did not. However, my answer is based on the premise that our ancestors did have better sense of hearing and smell than we do, and lost it. Since most mammals have better hearing and smell than we have, this is a good bet. But in any case, such things do occur in nature, and they have a good, fully Darwinian, explanation.

There are no real "limits" to Darwin's theory. His theory simply posits that living beings adapt genetically to their environment through mutation and natural selection. Those best suited to the environment survive and have more young. Those less suited survive less and have fewer young and may eventually die out. His theory essentially speaks of an on-going and endless series of trials and errors, with no inherent limitations to the theory (since he did not write anything about an endpoint or ultimate conclusion of the evolutionary process).

Suppose John an Suzi caveman have 3 kids. One is has the big ear advantage, one has smarts and one has both.

The one with the big ears hunts well his whole life and is able to feed and raise 2 kids.

The one with smarts uses tools and group communication to hunt and is able to feed and raise 6 kids.

The one with both smarts and big ears also uses tools and communication to hunt, since it is obviously the better option, and is also able to feed and raise 6 kids. His ears helped him be the best hunter in the group, but the food is distributed evenly, since the real best hunter was the "team".

So in this scenario, though good hearing is an advantage, it is minuscule compared to intelligence, an thus not a determining factor in human evolution.

If some standard Punnit Square calculations are done in series, forming a caveman family-tree, we will see a tendancy away from big ears.

Cool question.

Well, I must say there are plenty of animals more elegant than humans, like the cats, sleek and graceful. Even a skunk has a lot of beauty. So I don't suppose it has to do with elegance.

We have prominent noses and ears, while some animals have just nostrils and hidden ears (birds e.g.)

We probably weren't very good hunters, but developed language to work together in a hunt and to warn of predators.

Why we became dominant, I don't know. I have to believe an intelligence was guiding us, but now we have outrun our dominance by overusing our dominance. Ironic, isn't it?

why do you think these organs don't have any disadvantage? Ear is not just a thing attached to our head. The most sophisticated part of it, which is responsible for interpretation of sounds is inside the brain. well, i am not a biologist, i am a computer programmer and I think 'better' ears mean more appropriate data to analyze. So the brain is busy with analyzing and interpreting sounds instead of inventing something useful.

On the other hand, predators like tigers or snakes are perfect hunters but they cannot evolve into intelligent species like primates did, because of their perfection and specialization in hunting. Like, tiger's pawn is perfect for sneaking, running and killing, but not for creating a weapon for example.

The only limit of the theory of evolution is that it doesn't help explain the origins of life on Earth very well. Not that it has ever tried (regardless of what creationists/intelligent design proponents try to tell anyone).

I don't really think I understand your point. Characteristics on an organism are only "good" or "bad" in terms of their environment. The organism as a whole isn't "good" or "bad", it just fits into its environment or it doesn't.

I think you are assuming that the most recent common ancestor of all primates had as good a sense of hearing or sense of smell as the "best" primate example today. You have to remember that all other primates have been evolving along side humans. They might have needed better hearing or better sense of smell to better fit in their environment. Since humans have, throughout their short history, been fiddling with the environment to better suit them (instead of the other way around), they haven't had to develop as "good" a sense of hearing or smell.

The limit of Darwin's theory of evolution is that it is showing some mechanisms of adaptation within the species into sub-species (micro-evolution) while such a thing as progressive evolution from "simple" life forms to "higher" life form (macro-evolution) can not be shown by facts, but remains untestable theory. Newly discovered facts on DNA and the function of genes strongly support this limitation of Darwin's theory.

u cant classify charachters as advantageous or disadvantageous in that manner. i agree that apes and other primates have good hearing and smelling power .this is b'coz they had tremendous use 4 that. they only when decided to use their intelligence evolved into humans. their REQUIREMENT for strong olfaction and hearing got diminished and their use of intelligence increased.this caused the brain to get modified in a way. i believe that if you start dev. ur smelling sense (as the chemists) do than ikt might become better than the primates.

in the course of evolution we might as well see babies born with diff charachters than we have today, simply on the need for that. the people living in caves have different instincts than ours that too simply due to need. the animals need good senses as they have a use for that, we don't need it advantageous or not,hence those charachters have reduced.(eg. the tail.why don't we have it any more. simply because its need has reduced. we have hands for that, during the course of evolution as the man began to get food easily on land he stoped climbing trees and the need for tail reduced, so why have that ?)

did you know, that only about 50 yrs ago, when human babies are birthed, their eyes dont open immediately.

like kittens....

if you've seen the movie 'evolution' with the head and shoulder shampoo joke thing, remember that the creatures could not live on land because of the presence of oxygen in the air, if im not mistaken.... but once a creature was birthed in the presence of oxygen, it lived,..... but the species became different from that it was born from.... i forgot the term for it, (when a species is separated, and after many years and generations, these two species cannot interlink cus they are different)

notice, kids these days, become so invovled with technology at a much younger age than we started... evolution, is not a process where by just because we bcome intelligent, we lose other good properties to balance it.

evolution can take place because we dont use a part of ourselves as much as we used to...

look at cavemen, they used to have pretty long sharp fangs.... and big jaws. nowadays, as we evolve, our jaws are getting smaller, our fangs arent that sharp, and our teeth have to be removed cus of the size of our jaws.... cavemen had big jaws because they needed to chew on their food, back then, who cared about tender meat, or even cooked meat, they used the muscles so, that their jaws had to be big strong, and with fangs to chew their food... after time we got smarter, and thought of cutting our food into smaller pieces, after getting used to eating smaller chunks of food, our body readjust, because our mind tells us to,.... and altho changes arent so effective in us, but in our generations and years to come, the effect shows well...

thus like wise, we can develop better hearing and smelling senses, but one, we need pratice, so we get used to it,... and we use our body parts to the maximum, and also implement it in the generations below, and with many years, our hearing might become more sensitive!!

i think ppl who play instrunments have good hearing...

thus if their generation plays it, hopefully they will be able to have better hearing.... that is ofcourse, without accounting for any negative factors.... im only looking at this aspect without seeing negative influences like radiation, etc.

hope my words helped

Most educated people in Europe and the Americas during the 19th century had their first full exposure to the concept of evolution through the writings of Charles Darwin click this icon to hear the name pronounced. Clearly, he did not invent the idea. That happened long before he was born. However, he carried out the necessary research to conclusively document that evolution has occurred and then made the idea acceptable for scientists and the general public. This was not easy since the idea of evolution had been strongly associated with radical scientific and political views coming out of post-revolutionary France. These ideas were widely considered to be a threat to the established social and political order.

photo of Charles Darwin in late middle age

Charles Darwin

1809-1882

Charles Darwin was born into a moderately wealthy family in Shrewsbury, England. His father, Robert, had the largest medical practice outside of London at the time and his mother, Susannah Wedgwood, was from a family of wealthy pottery manufacturers. She died when Charles was only 8 years old. Thereafter, he was raised mostly by his father and older sisters. Charles grew up in comparative luxury in a large house with servants. However, this was a socially very conservative time in England that set narrow limits on a young man's behavior and future possibilities. The constraints on women in Darwin's social class were even greater. Most were given only enough education to efficiently manage the homes of their future husbands and raise their children. Young men were expected to go to university in order to prepare themselves to become medical doctors, military officers, or clerics in the Church of England. Most other occupations were considered somewhat unsavory.

At his father's direction, Charles Darwin started university at 16 in Edinburgh, Scotland as a medical student. He showed little academic interest in medicine and was revolted by the brutality of surgery. He dropped out after two years of study in 1827. His father then sent him to Cambridge University to study theology. It was there that his life's direction took a radical change. He became very interested in the scientific ideas of the geologist Adam Sedgwick and especially the naturalist John Henslow with whom he spent considerable time collecting specimens from the countryside around the university. At this time in his life, Darwin apparently rejected the concept of biological evolution, just as his mentors Sedgwick and Henslow did. However, Darwin had been exposed to the ideas of Lamarck about evolution earlier while he was a student in Edinburgh.

Following graduation from Cambridge in 1831 with a degree in theology, Darwin was clearly more interested in biology than he was in a clerical career. Fortunately, John Henslow was able to help him secure a berth on a British Navy mapping expedition that was going around the world on what would ultimately become a five year long voyage. Initially, Darwin's father refused to allow him to go but was eventually persuaded by Charles and even agreed to pay for his passage and for that of his man servant on the journey. They sailed two days after Christmas in 1831 aboard the survey ship H.M.S. Beagle with Darwin acting as an unpaid naturalist and gentleman companion for the aristocratic captain, Robert Fitzroy. Darwin was only 22 years old at the time. The Beagle was a compact 90 foot long ship with a crew of 74. There was little space, even for the captain. Because of its small size, it was generally thought by naval men that the Beagle was ill suited for the rough seas it would encounter, especially at the southern tip of South America. Darwin frequently suffered from sea sickness on the voyage.

It was during the beginning of the voyage that Darwin read the early books of Charles Lyell and became convinced by his proof that uniformitarianism provided the correct understanding of the earth's geological history. This intellectual preparation along with his research on the voyage were critical in leading Darwin to accept evolution. Especially important to the development of this understanding was his 5 weeks long visit to the Gal�pagos Islands click this icon to hear the preceding term pronounced in the Eastern Pacific Ocean. It was there that he began to comprehend what causes plants and animals to evolve, but he apparently did not clearly formulate his views on this until 1837.

Picture of HMS Beagle, from an 1841 watercolor map highlighting the route of H.M.S. Beagle in its around the world expedition--Britain to Brazil, Argentina, Chile, Galapagos Islands, New Zealand, Australia, South Africa, Brazil, and finally back to Britain

H.M.S. Beagle

Five year voyage of H.M.S. Beagle (1831-1836)

The Gal�pagos Islands have species found in no other part of the world, though similar ones exist on the west coast of South America. Darwin was struck by the fact that the birds were slightly different from one island to another. He realized that the key to why this difference existed was connected with the fact that the various species live in different kinds of environments.

Map of Gal�pagos Islands in relationship to South America 600 miles to the east

Darwin identified 13 species of finches in the Gal�pagos Islands. This was puzzling since he knew of only one species of this bird on the mainland of South America, nearly 600 miles to the east, where they had all presumably originated. He observed that the Gal�pagos species differed from each other in beak size and shape. He also noted that the beak varieties were associated with diets based on different foods. He concluded that when the original South American finches reached the islands, they dispersed to different environments where they had to adapt to different conditions. Over many generations, they changed anatomically in ways that allowed them to get enough food and survive to reproduce.

drawings showing heads of four of the Darwin finch species highlighting the differences in their beaks

Finches from the Gal�pagos Islands

Today we use the term adaptive radiation to refer to this sort of branching evolution in which different populations of a species become reproductively isolated from each other by adapting to different ecological niches click this icon to hear the preceding term pronounced and eventually become separate species.

diagram illustrating the adaptive radiation of descendent species from a common ancestor

Darwin came to understand that any population consists of individuals that are all slightly different from one another. Those individuals having a variation that gives them an advantage in staying alive long enough to successfully reproduce are the ones that pass on their traits more frequently to the next generation. Subsequently, their traits become more common and the population evolves. Darwin called this "descent with modification."

The Gal�pagos finches provide an excellent example of this process. Among the birds that ended up in arid environments, the ones with beaks better suited for eating cactus got more food. As a result, they were in better condition to mate. Similarly, those with beak shapes that were better suited to getting nectar from flowers or eating hard seeds in other environments were at an advantage there. In a very real sense, nature selected the best adapted varieties to survive and to reproduce. This process has come to be known as natural selection.

Darwin did not believe that the environment was producing the variation within the finch populations. He correctly thought that the variation already existed and that nature just selected for the most suitable beak shape and against less useful ones. By the late 1860's, Darwin came to describe this process as the "survival of the fittest." This is very different from Lamarck's incorrect idea that the environment altered the shape of individuals and that these acquired changes were then inherited.

painting of Thomas Malthus

Thomas Malthus

(1766-1834)

Nineteenth century critics of Darwin thought that he had misinterpreted the Gal�pagos finch data. They said that God had created the 13 different species as they are and that no evolution in beak shape has ever occurred. It was difficult to conclusively refute such counter arguments at that time. However, 20th century field research has proven Darwin to be correct.

In 1798, Thomas Malthus click this icon to hear the name pronounced, an English clergyman and pioneer economist, published Essay on the Principles of Population. In it he observed that human populations will double every 25 years unless they are kept in check by limits in food supply. In 1838, Darwin read Malthus' essay and came to realize that all plant and animal populations have this same potential to rapidly increase their numbers unless they are constantly kept in check by predators, diseases, and limitations in food, water, and other resources that are essential for survival. This fact was key to his understanding of the process of natural selection. Darwin realized that the most fit individuals in a population are the ones that are least likely to die of starvation and, therefore, are most likely to pass on their traits to the next generation.

click this icon in order to see the following video Who Was Charles Darwin?--video clip from PBS 2001 series Evolution

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drawing of dark and light colored peppered moths on a tree with dark colored bark and a tree with light bark

Dark moths on light colored bark are

easy targets for hungry birds but are

hidden on pollution darkened trees.

An example of evolution resulting from natural selection was discovered among "peppered" moths living near English industrial cities. These insects have varieties that vary in wing and body coloration from light to dark. During the 19th century, sooty smoke from coal burning furnaces killed the lichen on trees and darkened the bark. When moths landed on these trees and other blackened surfaces, the dark colored ones were harder to spot by birds who ate them and, subsequently, they more often lived long enough to reproduce. Over generations, the environment continued to favor darker moths. As a result, they progressively became more common. By 1895, 98% of the moths in the vicinity of English cities like Manchester were mostly black. Since the 1950's, air pollution controls have significantly reduced the amount of heavy particulate air pollutants reaching the trees, buildings, and other objects in the environment. As a result, lichen has grown back, making trees lighter in color. In addition, once blackened buildings were cleaned making them lighter in color. Now, natural selection favors lighter moth varieties so they have become the most common. This trend has been well documented by field studies undertaken between 1959 and 1995 by Sir Cyril Clarke from the University of Liverpool. The same pattern of moth wing color evolutionary change in response to increased and later decreased air pollution has been carefully documented by other researchers for the countryside around Detroit, Michigan. While it is abundantly clear that there has been an evolution in peppered moth coloration due to the advantage of camouflage over the last two centuries, it is important to keep in mind that this story of natural selection in action is incomplete. There may have been additional natural selection factors involved.

click this icon in order to see the following video Evolution of Camouflage--another example of natural selection in the insect world

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click this icon in order to see the following video Toxic Newts--the evolutionary arms race between predator and prey driving evolution

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Darwin did not rush his ideas about natural selection into print. He first concentrated his efforts on writhing the account of his voyage on the Beagle and analyzing the specimens that he brought back with him. An additional factor was the widespread Christian evangelical fervor in England during the 1830's and 1840's. He could have been charged with sedition and blasphemy for widely publishing his unpopular theory. After returning from the voyage around the world on H.M.S. Beagle, he settled down in England, married Emma Wedgwood (his wealthy first cousin), raised a large family, and quietly continued his research at his newly purchased country home 16 miles south of London. In 1842 and 1844, he wrote relatively short summaries of his theory, but they were not widely read outside of British scientific circles. It was not until he was 50 years old, in 1859, that he finally published his theory of evolution in full for his fellow scientists and for the public at large. He did so in a 490 page book entitled On the Origin of Species. It was very popular and controversial from the outset. The first edition came out on November 24, 1859 and sold out on that day. It went through six editions by 1872. The ideas presented in this book were expanded with examples in fifteen additional scientific books that Darwin published over the next two decades.

photo of Down House--Charles and Emma Darwin's home picture of Emma Darwin as a young woman

Down House--Charles and Emma Darwin's country

home where he wrote his major publications and

their family lived contentedly for 40 years.

Emma Darwin

1808-1896

Alfred Wallace

1823-1913

What finally convinced Darwin that he should publish his theory in a book for the general educated public was the draft of an essay that he received in the summer of 1858 from a younger British naturalist named Alfred Wallace click this icon to hear the name pronounced, who was then hard at work collecting biological specimens in Southeast Asia for sale to museums and private collectors. Darwin was surprised to read that Wallace had come upon essentially the same explanation for evolution. Being a fair man, Darwin later insisted that Wallace also get credit for the natural selection theory during debates over its validity that occurred at a meeting of the British Association for the Advancement of Science at Oxford University in 1860. We now know that Darwin deserves most of the credit. In 1837, one year after he returned from the voyage on the Beagle, he made detailed notes on the idea of evolution by means of natural selection. At that time Wallace was only 14. In addition, it was Darwin's book, rather than Wallace's essay, that had the most impact on the Victorian public. Darwin not only described the process of natural selection in more detail, but he also gave numerous examples of it. It was his On the Origin of Species that convinced most scientists and other educated people in the late 19th century that life forms do change through time. This prepared the public for the acceptance of earlier human species and of a world much older than 6000 years.

click this icon to hear the following audio interview Darwin and Victorian Culture--interview with Darwin's biographer, James Moore

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Gregor Mendel

1822-1884

Both Darwin and Wallace failed to understand an important aspect of natural selection. They realized that plant and animal populations are composed of individuals that vary from each other in physical form. They also understood that nature selects from the existing varieties those traits that are most suited to their environment. If natural selection were the only process occurring, each generation should have less variation until all members of a population are essentially identical, or clones of each other. That does not happen. Each new generation has new variations. Darwin was aware of this fact, but he did not understand what caused the variation. The first person to begin to grasp why this happens was an obscure Central European monk named Gregor Mendel click this icon to hear the name pronounced. Through plant breeding experiments carried out between 1856 and 1863, he discovered that there is a recombination of parental traits in offspring. Sadly, Darwin and most other 19th century biologists never knew of Mendel and his research. It was not until the beginning of the 20th century that Mendel's pioneer research into genetic inheritance was rediscovered. This was long after his death. He never received the public acclaim that was eventually showered on Darwin during his lifetime.

Charles Darwin's convincing evidence that evolution occurs was very threatening to many Christians who believed that people were created specially by God and that they have not changed biologically since that creation. The idea that there could have been prehistoric humans who were anatomically different from us was rejected for similar reasons. However, Charles Lyell's geological evidence that the earth must be much older than 6,000 years along with the rapidly accumulating fossil record of past evolution convinced educated lay people in the 1860's to think what had been unthinkable earlier.

painting of Boucher de Perthes in 1832

Boucher de Perthes

(1788-1868)

Archaeological confirmation of the existence of prehistoric Europeans had been accumulating since the 1830's. However, until the late 1850's, it had been widely rejected or misinterpreted. Much of this evidence had been collected by Jacques Boucher Cr�vecoeur de Perthes click this icon to hear the name pronounced, a customs officer in northern France during the early 1800's. His hobby was collecting ancient stone tools from deep down in the Somme River gravel deposits. Since he found these artifacts in association with the bones of extinct animals, he concluded that they must have been made at the time that those animals lived.

19th century drawing of a well shaped prehistoric hand ax in front and side views

Prehistoric artifact incorrectly thought

to be a "lightning bolt remnant"

Boucher de Perthes tried to publish his findings in 1838. They were rejected by all important scientists and scientific journals. The prehistoric stone tools usually were dismissed as being only "lightning stones" (i.e., the remnants of lightning bolts). However, by 1858, his claims were beginning to be accepted by some enlightened Western European scientists. Darwin's publication of On the Origin of Species the following year convinced even more educated people that Boucher de Perthes had been right.

Darwin's popularizing the idea of evolution also made it possible for scientists to begin to accept that some of the makers of Boucher de Perthes' prehistoric tools had already been discovered and that their bones were in museums. These bones had been found in several Western European countries during the first half of the 19th century. However, they had all been dismissed as being from odd looking modern people. During the 1860's, some were correctly determined to be from an earlier species or variety of people who had lived during the last ice age--i.e., long before recorded history. We now know that these ancient people were mostly Neandertals, who lived about 150,000-28,000 years ago.

NOTE: The phrase "survival of the fittest" was apparently first used in 1851 by the influential British philosopher Herbert Spencer (1820-1903) as a central tenet of what later became known as "Social Darwinism." He misapplied Darwin's idea of natural selection to justify European domination and colonization of much of the rest of the world. Social Darwinism was also widely used to defend the unequal distribution of wealth and power in Europe and North America at the time. Poor and politically powerless people were thought to have been failures in the natural competition for survival. Subsequently, helping them was seen as a waste of time and counter to nature. From this perspective, rich and powerful people did not need to feel ashamed of their advantages because their success was proof that they were the most fit in this competition. Despite misgivings by Alfred Wallace and other naturalists, Charles Darwin began to use "survival of the fittest" as a synonym for "natural selection" in the 5th edition of Origin of Species, which was published in 1869.

NOTE: H.M.S. Beagle, the famous ship that took Charles Darwin on his 1831-1836 voyage around the world, had a rather mundane history following her return to England. She was transferred by the British Navy to the Customs and Excise Department and was used to catch smugglers along the southeast coast of England. The Beagle was finally sold for scrap in 1870 after 50 years of service.