Home / Science / “Missing link”? What missing link? – The evidence for the theory of evolution

“Missing link”? What missing link? – The evidence for the theory of evolution

“We are risen apes, not fallen angels.”

J. Anderson Thomson

According to the 2005 Eurobaromoeter (p. 220) only 55% of Greeks respond affirmatively to the claim “Humans, as we know them today, developed from earlier species of animals”. A quick search on youtube with the query “theory of evolution” will bring out a plethora of posts against the theory rather than for it! Bad education and religious dogma have convinced a majority of Greeks (among others) that the theory of evolution is…just a theory, yet to be proven right. The usual arguments against it come from the religious spectrum, and I hope they will be answered below.

One of them is the infamous “missing link” between ape and man: Since we come from lower animals, which is the intermediate organism that later became homo sapiens? The question rose in the time of Darwin himself, a time, though, that no human fossils had been found, and therefore it could not be answered in a satisfactory manner, but just on principle. Since then, the creationists have been taught (by each other) to repeat the aforementioned question as if it is the definitive argument against evolution. In reality, we are lucky to have any fossils at all, let alone a humanoid fossil. We might as well have none; the theory would stand just as well. Besides, since Darwin we have found several missing links, as is shown in the diagram below.

Fossils of our recent ancestors (source)
Fossils of our recent ancestors (source)

 

The problem with creationist is that every time the fossil of a new species is found, they claim that it presents two new gaps in the evolutionary chain. So, if we find a species B between species A and C, they will say that a species is missing between A and B and another one between B and C. They hypocritically demand perfect evidence from science, though none to support their own dogma. It is unrealistic to expect to find a fossil of every species ever existed, but this does not hinder the plausibility of evolution, it’s just an unfortunate fact. Most species don’t even become fossilized to begin with.

The word “theory” is used in everyday language as a synonym to “hypothesis” or “point of view”. But in the world of science the notion of theory is a sum of claims that explain observations in the real world. Starting from the observance of a phenomenon, a scientist makes a hypothesis, which leads to the formation of a model. This model then implies certain predictions, which have to be examined whether they are verifiable or not. Then, experimentation is performed (or observations in nature), which presents us with results. If these results are identical with the predictions of our model, then the hypothesis is considered to work (to have been proven correct) and is upgraded to theory. The more we can make verified predictions on the premise of the theory, the more soundly it is established.

So, which are the claims of the theory of evolution, and what kind of predictions can we use it for?

  1. Organisms evolve.

I am referring here to heredity, a fact so obvious, it hardly needs mentioning. It’s not even a Darwinian discovery, as it is known and used for millennia by humans in farming and the domestication of wolf, through its guided evolution to the dog. As an example, we can see in the picture below the evolution of a wild banana to its current form.

From the wild Musa Balbisiana to the Cavendish banana (more here)
From the wild Musa Balbisiana to the Cavendish banana (more here)

 

Verified predictions: Crossing of various dog breeds for a desired result, cultivation using big-sized fruits so that the future population size is big, eugenics…

  1. Evolution occurs gradually.

There never was an ape to give birth to a human. To be precise, there never was a set of parents to procreate an organism belonging in another species. The random mutations of every generation don’t produce a dramatic, noticeable variation in the offspring, but minimal changes in its genome, that aggregate through the passage of time, so that a very distant descendant will be so different than the said parents, that we will categorize as another species. A useful comparison is this: Imagine you have a portrait photograph of yourself for every day of your life. If I was to show you two consecutive photos, would you be able to recognize which came first and which came second? This doesn’t mean there are no changes on your face. If you compare a photo from when you were a baby and one from last month, the differences are quite obvious. Evolution works in a similar way; you can’t tell the difference between consecutive generations, but given enough time you will get the distinction from some proverbial bacteria to the homo sapiens. Let’s not forget that life on Earth started around 3.5 billion years ago.

evolution 3

Prediction: We will have to be able to discover ancestors that lead to a modern species. Indeed, we continuously find fossils of species that modern animals (including humans) come from, and the mutations are gradual and slow.

  1. Evolution leads to variation of species – the evolution is not linear (speciation). Or, the other way around, we can, by going back in time, find the common ancestor of any two species.

If the theory of evolution spoke of linear evolution, the current abundance of species could not be explained. On the contrary, the theory speaks of branches in the “tree of life”. Species A doesn’t lead to species B, but branches to B and C. The fact that we share 98% of our DNA with modern chimps (the biggest percentage than with any other animal) means that we and the chimps have the most recent common ancestor than with any other living organism. With orangutans we have an older common ancestor, so the percentage will be lower.

Some of our closest cousins (source)
Some of our closest cousins (source)

 

Here I have to address the common erroneous concept of humans evolving from apes. We must not forget that apes are modern animals, as much evolved as humans, just not in the same way.

Verified prediction: Like above, we keep finding fossils of species that, because they have been geographically separated from their ancestors, have evolved differently, according to the new environment. A characteristic example is the slight variations of the species of the Galapagos Islands that Darwin visited and helped him form his theory.

The slightly varied finches of the Galapagos Islands
The slightly varied finches of the Galapagos Islands

 

  1. The mechanism of evolution is natural selection.

In nature, due to errors during the DNA replication, mutations appear in every generation. Some mutations are insignificant, some not so much. For example, the peppered moth, up to mid 19th century was light-coloured. Since it rested upon light-coloured trees and lichens of a similar colour, it was conveniently camouflaged. Whenever a darker coloured moth was born, its natural enemies were easy to spot it and therefore it was statistically less likely to grow old enough to procreate and pass on the genes that caused its color to be darker. But by the end of the century, 98% of the population was dark. What had happened? The industrial revolution did. Because of heavy air pollution the trunks of the trees turned darker, therefore the roles were switched and it was the white descendants to fall victims of heredity. So the genes for the darker color prevailed.

What kind of prediction can we make based on this? If pollution was to be decreased the moths should again become light-coloured. Which is what actually happened with later improved environmental standards; illustrating the effect the natural habitat has on the evolution of organisms.

There are many other ways to approach the proof of evolution. Molecular genetics, geographical distribution, fossil records and actual observation are sources of evidence for the historical accuracy of evolution.

To analyse molecular genetics data is beyond the limits of this article and its writer. A good start for the curious reader would be this.

Geographical distribution: Plants and animals are found on this planet in particular regions but not on others, even if they could survive in both. The Galapagos Islands are already mentioned as an example. Let’s say there is a land mass that, for whichever reason (earthquake, flood, a river changing course…) is separated into two regions, causing a species to separate into two, now independent, populations. Since the theory of evolution speaks of random mutations, even if the climatic conditions are the same in the two regions, the evolution of one population will lead the species to a different path than that of the second. This is one of the reasons there are several species of turtles and finches in the Galapagos. This is also why we find marsupials almost exclusively in the isolated Australia. The examples are innumerous.

For us to observe evolution taking place in front of our eyes, when our subject is a mammal, is extremely difficult due to the long period any mammal needs to reach the age of procreation. It is, however, considerably easier to observe in bacteria that live a few hours (or insects like the aforementioned moths). The biologist Richard Lenski started a still running experiment in 1988 where he used the e-coli bacteria to observe its evolutionary changes, if any. Up to 2010 he managed to “grow” 50,000 generations of e-coli, with dozens of assimilated and beneficial genetic mutations.

We can also see evolution in bacteria, as any of you can attest to, having taken an antibiotic that didn’t work because the bacteria had already mutated into a species the drug could not be designed for.

Fossil records give the most evident reason to believe there were intermediate species between a modern organism and some ancient common ancestor. There have been discovered literally millions of fossils around the world (some times of the same species) and what makes this really important is that all of them are dated in the period and found in the region that we would expect them to have lived, if they had gradually evolved through heredity, exactly as Darwin’s theory describes. In fact, it would only take one fossil dated in the wrong period or found in the wrong place to disprove the entire theory of evolution, but all the millions of found fossils confirm the theory! The example the biologist J.B.S. Haldane gave when asked what it would take for him to dismiss the theory of evolution was “fossil rabbits in the Precambrian”. None such fossils have been found.

So, is the theory of evolution falsifiable? Of course it is! In fact, every scientific theory is. A list of data that would crush it, if they were true, is this:

  • Fossils in the wrong time/place
  • Absence of genetic variety in the same species
  • An assimilated genetic mutation that is not advantageous to the “current” species, but only to the next (more evolved) one.
  • Mutations harmful to the individual but beneficial to the population.
  • Mutations that could not have been evolved gradually, but only suddenly.
  • Observation of altruistic behaviour among non relatives in non social animals.

The list is long, but there has appeared no threat to the theory such as the above.

Another important point is that we find many errors in biological organisms, including humans. They are errors only in the sense that one would not think an intelligent designer would make. A characteristic example is a nerve that starts off in the brain and ends up on the larynx. You would expect the nerve to be a short straight line, since the distance is extremely short. What we find in a human though, is a half a meter long nerve, starting from the brain, bypassing the larynx by millimeters, going down the chest, making a loop around a heart vein, until it finally reaches the larynx once again. In a giraffe, this nerve is a few meters long. An all-wise designer to have created this mess, is something that doesn’t quite add up. The theory of evolution offers a description of how this came to be: In a fish, our distant ancestors (not modern fish of course), since there is no neck, the loop I mentioned is in fact the shortest route for the nerve to reach the larynx. When the neck appeared in the mammals, the heart gradually descended, dragging the nerve along with it.

There is an abundance of this kind of designer flaws that only evolution can explain.

I hope the historical truth of evolution is obvious by now. The bibliography is of course limitless, I would suggest to any doubtful or curious reader any work of Richard Dawkins, who does a great job of popularizing his scientific knowledge, giving the theory of evolution a redemptive role, showing us how much we share with plants and animals, against the narrow-minded vision of the history denying creationists who try to alter the facts to fit their predetermined views.

We are risen apes, not fallen angels.

evolution 6

Sources:

(from which the title of this article is inspired)

Evolution in front of our eyes – Peppered moths

Evolution in front of our eyes –Richard Lenski’s experiment on e-coli bacteria.

Designer flaws or heredity?

Giraffe’s anatomy.

A short presentation of the theory of evolution.

Interview of Richard Dawkins on evolution.

Jerry Coyne’s presentation on the evidence for evolution.

Carl Sagan presents the evolution of man.

Check Also

Darwin: Heritage and Misunderstandings – Morality, Irreverence, Eugenics

“I cannot persuade myself that a beneficent & omnipotent God would have designedly created the …

Leave a Reply

Your email address will not be published. Required fields are marked *