CureZone   Log On   Join
golfegg Views: 2,485
Published: 17 years ago
Status:       R [Message recommended by a moderator!]


I don't understand why it's so hard for you to present evidence for evolution Corinthian? I'll help you out I guess, since you seem so evidence challanged.  Here's a good starting point. Let's see what they say!

Holes in the Theory

The theory of evolution is just that -- a theory. According to "The American Heritage Dictionary," a theory is:

A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena.

Evolution is a set of principles that tries to explain how life, in all its various forms, appeared on Earth. The theory of evolution succeeds in explaining why we see bacteria and mosquitoes becoming resistant to antibiotics and insecticides. It also successfully predicted, for example, that X-ray exposure would lead to thousands of mutations in fruit flies.
Many theories are works in progress, and evolution is one of them. There are several big questions that the theory of evolution cannot answer right now. This is not unusual. Newtonian physics worked really well for hundreds of years, and it still works well today for many types of problems. However, it does not explain lots of things that were eventually answered by Einstein and his theories of relativity. People create new theories and modify existing ones to explain the unexplained.
In answering the open questions that still remain unsolved, the theory of evolution will either become complete or it will be replaced by a new theory that better explains the phenomena we see in nature. That is how the scientific process works.
Here are three common questions that are asked about the current theory of evolution:
  • How does evolution add information to a genome to create progressively more complicated organisms?
  • How is evolution able to bring about drastic changes so quickly?
  • How could the first living cell arise spontaneously to get evolution started?
Let's look at each of these questions briefly in the following sections.

Question 1: How Does Evolution Add Information?

The theory of evolution explains how strands of DNA change. An X-ray, cosmic ray, chemical reaction or similar mechanism can modify a base pair in the DNA strand to create a mutation, and this modification can lead to the creation of a new protein or enzyme.

The theory of evolution further proposes that billions of these mutations created all of the life forms we see today. An initial self-replicating molecule spontaneously formed. It evolved into single-cell organisms. These evolved into multi-cell organisms, which evolved into vertebrates like fish, and so on. In the process, DNA structures evolved from the asexual single-strand format found in bacteria today into the dual-strand chromosomal format found in all higher life forms. The number of chromosomes also proliferated. For example, fruit flies have five chromosomes, mice have 20, humans have 23 and dogs have 39.

Evolution's mutation mechanism does not explain how growth of a genome is possible. How can point mutations create new chromosomes or lengthen a strand of DNA? It is interesting to note that, in all of the selective breeding in dogs, there has been no change to the basic dog genome. All breeds of dog can still mate with one another. People have not seen any increase in dog's DNA, but have simply selected different genes from the existing dog gene pool to create the different breeds.
One line of research in this area focuses on transposons, or transposable elements, also referred to as "jumping genes." A transposon is a gene that is able to move or copy itself from one chromosome to another. The book "Molecular Biology of the Cell" puts it this way:
Transposable elements have also contributed to genome diversity in another way. When two transposable elements that are recognized by the same site-specific recombination enzyme (transposase) integrate into neighboring chromosomal sites, the DNA between them can become subject to transposition by the transposase. Because this provides a particularly effective pathway for the duplication and movement of exons (exon shuffling), these elements can help create new genes.
Another area of research involves polyploidy. Through the process of polyploidy, the total number of chromosomes can double, or a single chromosome can duplicate itself. This process is fairly common in plants, and explains why some plants can have as many as 100 chromosomes.
The amount of research in this area is truly remarkable and is teaching scientists amazing things about DNA.

Question 2: How Can Evolution Be So Quick?

Imagine that you create a very large cage and put a group of mice into it. You let the mice live and breed in this cage freely, without disturbance. If you were to come back after five years and look into this cage, you would find mice. Five years of breeding would cause no change in the mice in that cage -- they would not evolve in any noticeable way. You could leave the cage alone for a hundred years and look in again and what you would find in the cage is mice. After several hundred years, you would look into the cage and find not 15 new species, but mice.

The point is that evolution in general is an extremely slow process. When two mice breed, the offspring is a mouse. When that offspring breeds, its offspring is a mouse. When that offspring breeds... And the process continues. Point mutations do not change this fact in any significant way over the short haul.

Carl Sagan, in "The Dragons of Eden," put it this way:
The time scale for evolutionary or genetic change is very long. A characteristic period for the emergence of one advanced species from another is perhaps a hundred thousand years; and very often the difference in behavior between closely related species -- say, lions and tigers -- does not seem very great. An example of recent evolution of organ systems in humans is our toes. The big toe plays an important function in balance while walking; the other toes have much less obvious utility. They are clearly evolved from fingerlike appendages for grasping and swinging, like those of arboreal apes and monkeys. This evolution constitutes a respecialization -- the adaptation of an organ system originally evolved for one function to another and quite different function -- which required about ten million years to emerge.
The fact that it takes evolution 100,000 or 10 million years to make relatively minor changes in existing structures shows just how slow evolution really is. The creation of a new species is time consuming.
On the other hand, we know that evolution can move extremely quickly to create a new species. One example of the speed of evolution involves the progress mammals have made. You have probably heard that, about 65 million years ago, all of the dinosaurs died out quite suddenly. One theory for this massive extinction is an asteroid strike. For dinosaurs, the day of the asteroid strike was a bad one, but for mammals it was a good day. The disappearance of the dinosaurs cleared the playing field of most predators. Mammals began to thrive and differentiate.
Example: The Evolution of Mammals
65 million years ago, mammals were much simpler than they are today. A representative mammal of the time was the species Didelphodon, a smallish, four-legged creature similar to today's opossum.
In 65 million years, according to the theory of evolution, every mammal that we see today (over 4,000 species) evolved from small, four-legged creatures like Didelphodon. Through random mutations and natural selection, evolution has produced mammals of striking diversity from that humble starting point:
  • Humans
  • Dogs
  • Moles
  • Bats
  • Whales
  • Elephants
  • Giraffes
  • Panda bears
  • Horses

Evolution has created thousands of different species that range in size and shape from a small brown bat that weighs a few grams to a blue whale that is nearly 100 feet (30.5 m) long.

Let's take Carl Sagan's statement that "A characteristic period for the emergence of one advanced species from another is perhaps a hundred thousand years, and very often the difference in behavior between closely related species -- say, lions and tigers -- does not seem very great." In 65 million years, there are only 650 periods of 100,000 years -- that's 650 "ticks" of the evolutionary clock.
Imagine trying to start with an opossum and get to an elephant in 650 increments or less, even if every increment were perfect. An elephant's brain is hundreds of times bigger than an opossum's, containing hundreds of times more neurons, all perfectly wired. An elephant's trunk is a perfectly formed prehensile appendage containing 150,000 muscle elements. Starting with a snout like that of an opossum, evolution used random mutations to design the elephant's snout in only 650 ticks. Imagine trying to get from an opossum to a brown bat in 650 increments. Or from an opossum to a whale. Whales have no pelvis, have flukes, have very weird skulls (especially the sperm whale), have blow holes up top, have temperature control that allows them to swim in arctic waters and they consume salt water rather than fresh. It is difficult for many people to imagine that sort of speed given the current theory.
Example: The Evolution of the Human Brain
Here is another example of the speed problem. Current fossil evidence indicates that modern humans evolved from a species called Homo erectus. Homo erectus appeared about 2 million years ago. Looking at the skull of Homo erectus, we know that its brain size was on the order of 800 or 900 cubic centimeters (CCs).

Modern human brain size averages about 1,500 CCs or so. In other words, in about 2 million years, evolution roughly doubled the size of the Homo erectus brain to create the human brain that we have today. Our brains contain approximately 100 billion neurons today, so in 2 million years, evolution added 50 billion neurons to the Homo erectus brain (while at the same time redesigning the skull to accommodate all of those neurons and redesigning the female pelvis to let the larger skull through during birth, etc.).

Let's assume that Homo erectus was able to reproduce every 10 years. That means that, in 2 million years, there were 200,000 generations of Homo erectus possible. There are four possible explanations for where the 50 billion new neurons came from in 200,000 generations:
  • Every generation, 250,000 new neurons were added to the Homo erectus brain (250,000 * 200,000 = 50 billion).
  • Every 100,000 years, 2.5 billion new neurons were added to the Homo erectus brain (2,500,000,000 * 20 = 50 billion).
  • Perhaps 500,000 years ago, there was a spurt of 20 or so closely-spaced generations that added 2.5 billion neurons per generation.
  • One day, spontaneously, 50 billion new neurons were added to the Homo erectus brain to create the Homo sapiens brain.

* In an absolutely facinating experiment first reported in July 2002, scientists modified a single mouse gene and created mice with brains 50% larger than normal. This experiment shows that a point mutation can, in fact, have an immense effect on brain size. It is still unknown whether the larger brains make the mice smarter or not, but it is easy to imagine later mutations refining the wiring of these millions of new neurons.

In another fascinating study, researches have identified minimal changes in an amino acid on a single gene that have a profound effect on speech processing in humans.
It does appear that tiny changes in single genes can have very large effects on the species.
None of these scenarios is particularly comfortable. We see no evidence that evolution is randomly adding 250,000 neurons to each child born today, so that explanation is hard to swallow. The thought of adding a large package of something like 2.5 billion neurons in one step is difficult to imagine, because there is no way to explain how the neurons would wire themselves in. What sort of point mutation would occur in a DNA molecule that would suddenly create billions of new neurons and wire them correctly?* The current theory of evolution does not predict how this could happen.

One line of current research is looking at the effect of very small changes in DNA patterns during embryonic development. Any new animal, be it a mouse or a human, starts life as a single cell. That cell differentiates and develops into the complete animal. A tremendous amount of signaling happens between cells during the development process to ensure that everything ends up in the right place. Tiny changes in these signaling processes can have very large effects on the resulting animal. This is how the human genome, with at most 60,000 or so genes, is able to specify the creation of a human body containing trillions of cells, billions of carefully wired neurons and hundreds of different cell types all brilliantly sculpted into organs as diverse as the heart and the eyes. The book "Molecular Biology of the Cell" puts it this way:

Humans, as a genus distinct from the great apes, have existed for only a few million years. Each human gene has therefore had the chance to accumulate relatively few nucleotide changes since our inception, and most of these have been eliminated by natural selection. A comparison of humans and monkeys, for example, shows that their cytochrome-c molecules differ in about 1 percent and their hemoglobins in about 4 percent of their amino acid positions. Clearly, a great deal of our genetic heritage must have been formed long before Homo sapiens appeared, during the evolution of mammals (which started about 300 million years ago) and even earlier. Because the proteins of mammals as different as whales and humans are very similar, the evolutionary changes that have produced such striking morphological differences must involve relatively few changes in molecules from which we are made. Instead, it is thought that the morphological differences arise from differences in the temporal and spatial pattern of gene expression during embryonic development, which then determine the size, shape and other characteristics of the adult.
In other words, there just are not that many differences in the DNA of a human and a whale, yet humans and whales look totally different. Small collections of DNA mutations can have a very big effect on the final result.
Right now, the signaling mechanisms that wire up the 100 billion cells in the human brain are something of a mystery. How can the mere 60,000 genes in the human genome tell 100 billion neurons how to precisely wire themselves in the human brain? No one right now has a clear understanding of how so few genes can meticulously wire so many neurons. In a developing fetus in the womb, DNA is correctly creating and wiring up millions of cells per minute. Given that DNA does wire up a working human brain every time a baby is born, it may be the case that DNA has special properties that make evolution work more efficiently. As the mechanisms become better understood, the effects of DNA mutations during development will become better understood as well.

Question 3: Where Did the First Living Cell Come From?

In order for the principles of mutation and natural selection in the theory of evolution to work, there have to be living things for them to work on. Life must exist before it can to start diversifying. Life had to come from somewhere, and the theory of evolution proposes that it arose spontaneously out of the inert chemicals of planet Earth perhaps 4 billion years ago.

Could life arise spontaneously? If you read How Cells Work, you can see that even a primitive cell like an E. coli bacteria -- one of the simplest life forms in existence today -- is amazingly complex. Following the E. coli model, a cell would have to contain at an absolute minimum:

  • A cell wall of some sort to contain the cell
  • A genetic blueprint for the cell (in the form of DNA)
  • An enzyme capable of copying information out of the genetic blueprint to manufacture new proteins and enzymes
  • An enzyme capable of manufacturing new enzymes, along with all of the building blocks for those enzymes
  • An enzyme that can build cell walls
  • An enzyme able to copy the genetic material in preparation for cell splitting (reproduction)
  • An enzyme or enzymes able to take care of all of the other operations of splitting one cell into two to implement reproduction (For example, something has to get the second copy of the genetic material separated from the first, and then the cell wall has to split and seal over in the two new cells.)
  • Enzymes able to manufacture energy molecules to power all of the previously mentioned enzymes
Obviously, the E. coli cell itself is the product of billions of years of evolution, so it is complex and intricate -- much more complex than the first living cells. Even so, the first living cells had to possess:
  • A cell wall
  • The ability to maintain and expand the cell wall (grow)
  • The ability to process "food" (other molecules floating outside the cell) to create energy
  • The ability to split itself to reproduce
Otherwise, it is not really a cell and it is not really alive. To try to imagine a primordial cell with these capabilities spontaneously creating itself, it is helpful to consider some simplifying assumptions. For example:
  • Perhaps the original energy molecule was very different from the mechanism found in living cells today, and the energy molecules happened to be abundant and free-floating in the environment. Therefore, the original cell would not have had to manufacture them.
  • Perhaps the chemical composition of the Earth was conducive to the spontaneous production of protein chains, so the oceans were filled with unimaginable numbers of random chains and enzymes.
  • Perhaps the first cell walls were naturally forming lipid spheres, and these spheres randomly entrapped different combinations of chemicals.
  • Perhaps the first genetic blueprint was something other than DNA.
These examples do simplify the requirements for the "original cell," but it is still a long way to spontaneous generation of life. Perhaps the first living cells were completely different from what we see today, and no one has yet imagined what they might have been like. Speaking in general terms, life can only have come from one of two possible places:
  • Spontaneous creation - Random chemical processes created the first living cell.
  • Supernatural creation - God or some other supernatural power created the first living cell.
And it doesn't really matter if aliens or meteorites brought the first living cell to earth, because the aliens would have come into existence through either spontaneous creation or supernatural creation at some point -- something had to create the first alien cells.
Most likely, it will be many years before research can completely answer any of the three questions mentioned here. Given that DNA was not discovered until the 1950s, the research on this complicated molecule is still in its infancy, and we have much to learn.

The Future of Evolution

One exciting thing about the theory of evolution is that we can see its effects both today and in the past. For example, the book "Evolution" mentions this:

The earliest known reptiles are so amphibian-like that their assignment to one category or the other is largely a matter of opinion. In this area of life, however, there was no missing link; all the gradations from amphibian to reptile exist with a clarity seldom equaled in paleontology.

In other words, there is plenty of evidence, past and present, for some sort of evolutionary process. We see it in bacteria and insects today, and we see it in the fossil record through the development of millions of species over millions of years.
After thinking about questions like the three mentioned in the previous sections, different people come to different conclusions. In the future, there are three possible scenarios for the theory of evolution:
  • Scientists will come to a complete understanding of DNA and show how mutations and natural selection explain every part of the development of life on this planet.
  • Scientists will develop a new theory that answers the questions posed above to almost everyone's satisfaction, and it will replace the theory of evolution that we have today.
  • Scientists will observe a completely new phenomenon that accounts for the diversity of life that we see today. For example, many people believe in creationism. In this theory, God or some other supernatural power intervenes to create all of the life that we see around us. The fossil record indicates that hundreds of millions of new species have been created over hundreds of millions of years -- Species creation is an intense and constant process with an extremely long history. If scientists were to observe the creation process occurring the next time a major new species comes into existence, they could document it and understand how it works.
Let's assume that the theory of evolution as currently stated is the process that did bring about all of the life that we see today. One compelling question is: "What happens next?" Evolution must be at work right now. Our species, Homo sapiens, only appeared about 40,000 years ago. What does evolution have in store for human beings, and how will the change manifest itself?
  • Will a child appear one day whose brain is twice as big as any normal human brain? If so, what will be the capabilities of that brain, and how will it differ from the brain seen today? Or are our brains slowly evolving right now?
  • Will children appear one day who have more than 23 chromosomes? If so, what will be the effects of the new chromosomes?
  • Will man learn how to control or accelerate evolution through genetic engineering? Once we completely understand different genomes, will we be able to engineer evolutionary steps that lead to new species on a much faster schedule? What would those species look like? What would we design them to do?

These are all fascinating questions to think about. They reveal just how big an effect evolution can have. Given enough time, evolution could completely alter life on this planet by disposing of the species we see today and creating new ones.



Printer-friendly version of this page Email this message to a friend

This Forum message belongs to a larger discussion thread. See the complete thread below. You can reply to this message!


Donate to CureZone

CureZone Newsletter is distributed in partnership with

Contact Us - Advertise - Stats

Copyright 1999 - 2023

0.391 sec, (12)