Introduction to evolution 

There is an enormous variety of plants and animals living on the earth, at least 9 million species. Some have existed for many millions of years in more or less the same shape; others changed their form and are of more recent date, but even the new and young species man (Homo sapiens) has existed for 200,000 years. Over time, many species and whole groups of species have developed, and many species and groups, like dinosaurs, became extinct again.

New species emerge from existing species. How this happens is described in the theory of evolution, also called neo-Darwinism. Charles Darwin laid the foundation for this theory in 1859 in his book "On the Origin of Species" after a long voyage aboard the ship The Beagle many years before. Later on, his theory was extended with new data and insights, therefore it is now called neo-Darwinism.

On this page neo-Darwinism will be briefly explained and commented on. On the following pages the evolution of the horse as a well documented example is discussed, followed by the evolution of dinosaurs and apes and man. The theories of Louis Bolk and Jos Verhulst will be used.

Neo-Darwinism

All plants and animals of a species are a little different. In humans this is clear, and in cows, dogs and horses, but if you observe with enough attention, you will notice it in all other species. This has two causes. The first is that small differences in the genetic material, the DNA, occur. These differences arise because the DNA mutates and changes a little all the time. This gives the organism slightly different characteristics. And because of these small differences, one organism responds slightly different to its environment than another. One organism fits a little better in its environment than another and therefore has a greater chance to survive and to reproduce itself. This is called "survival of the fittest", the survival of the organism that fits best in its environment. The organisms that do not fit are eliminated. This is why a population of organisms can gradually change.

Not only the DNA is different, the environment is always slightly different too and can be somewhat better for one organism than for the other. This allows an organism a slightly better chance to have offspring, too. Because changes in the environment go first one way and then the other, they stay roughly the same over a long period of time and organisms stay the same for a long time too. Although the discoveries of fossils prove that new species arise on the very long term (millions of years), the change has never been seen.

All organisms have a slightly different chance of survival and reproduction, because of their slightly different characteristics. The environment determines which organism is successful and which is not. Organisms that reproduce are called successful and better adapted. Yet coincidence seems to play a serious role. The victims of hunting predators are mostly young animals. They are weaker than adults, but does that mean that only the weaker animals are caught, or is it also a case of being in the wrong place at the wrong time, of bad luck?

Competition

The premise of neo-Darwinism is that all organisms of a species are in competition with each other. Every organism has more offspring than can survive and reproduce. Many or most of the offspring do not reach the age to mate. And many cannot reproduce, because they lose the final fight. There is a "struggle for life", which is fought over basic necessities (food, water, space). Because there is too much offspring, there is always shortage and organisms fight for their needs. Plants compete for nutrients and light, animals for food, females and a safe nesting place.

The emergence of new species

New species arise because part of the population is separated from the rest for a long time by a barrier and the circumstances are different or change. Such a separation may result from climate change, causing glaciers or deserts to form an impassable barrier, or by the diversion of a river, the creation of a lake or sea or the formation of mountains. For small organisms a highway can be a barrier!

Because the conditions in one part are different or change, the soil may become drier or wetter and the vegetation may change, or different plants may arise. Individuals with different characteristics than in the area 'behind' the barrier do now have the chance to reproduce themselves. The selection pressure is different. The result is that some characteristics change in one part. If the barrier lasts long enough, the two populations will become quite different. When the barrier eventually disappears, the organisms from both sides do not recognize each other anymore, or the chromosomes do not fit anymore and they do not breed with each other. Then there is a new species.

Famous are the so-called Darwin finches of the Galapagos Islands, a remote archipelago in the Pacific. Probably a small group of finches was blown there with a gale. In the course of time some birds flew to the other islands and found different environments to which they adjusted. In this case, the environment (living in trees or on the ground), the type of food (seeds or insects) and the size of the seeds seem to be the factors that were important for the emergence of new species.

An example: because the size of the bill varies slightly, finches with larger beaks have an advantage if the seeds on the other island are larger. They can eat more and have more energy to successfully reproduce and raise their offspring. Slowly finches with larger beaks get the overhand. When the finches fly back to the old island after a long time, they meet finches with smaller beaks. Because both now eat different seeds, there is no competition and two species exist. Then other characteristics can also gradually change, like the colour of the feathers.

Darwin finches; 14 species of finches that arose from a group of ancestors live on the Galapagos islands. They differ in size, behaviour and bill-shape, which is related to the type of food and size of the seeds they eat. There are groundfinches and treefinches, herbivores, insectivores and mixed feeders with a preference for one of both. Animals on the left - and right side have a strong preference for one type of food, food preference is lower for animals in the middle of the drawing.

To avoid competition, some individuals can start to use a different environment, for example some finches may start to forage on the ground and thus have no more trouble from the finches that continue foraging in the trees. This also causes new species. Through both types of changes there are now 14 species of finches, all originated from the one.

In the second form of speciation, there is no barrier, but some organisms move to a different environment. This happens quite often. The apple maggot first foraged on the berries of the hawthorn. Some maggots transferred to apples, now their staple food. The apple and hawthorn maggot are still able to breed, but due to the different environment, they do not meet anymore. Over time it is expected, that this allows the apple maggot to become a new species.

Specialization

Survival of the fittest means that organisms get more and more adapted to their environment and move along with the changes of the environment. In the course of evolution the adaptations cause species to become ever more specialized. At the same time they become more and more dependent on the conditions associated with those adaptations. A cheetah needs to encounter an antelope on the plains, in the woods it does not have a chance. The caterpillar of the cinnabar moth needs ragwort as a feeding plant, without it, it cannot survive. The monarch butterfly feeds on milkweed in its caterpillar stage, while the plant is pollinated by the butterflies. Grass and grazers have a common evolution, in which the grasses became better suited to be eaten and the herbivores to eat and digest the grasses. Should grass disappear from an area, then grazers will also disappear.

The giraffe

Giraffes have long necks to eat leaves high in the canopy of acacia trees. It is a fact that they do this. Their long legs, long neck, long and narrow jaw and long tongue make these animals suitable to pluck the leaves of the acacia among the thorns. The long neck appeared in the cause of evolution. Ancestors of today's giraffe had short necks. Yet, this statement cannot be maintained. During the dry season, when food is scarce and competition most severe, giraffes prefer to eat from low bushes (see video). Only if there is much food and little competition, they eat from the high acacias. In the first sentence the 'have ... to' is not correct, as there is no causal connection. It should be: giraffes have long necks and eat high in the canopy of acacia trees.

It is also thought that giraffes have long necks to fight with each other, which the males do. The one with the longest and toughest neck can mate and pass on his genes. A problem with this explanation is that giraffes with short necks should already have shown this behaviour. If not, why should the neck have become longer? And it does not explain the long legs and long tongue.

A third explanation, namely that the long neck and the big eyes enable the giraffe to see enemies from a distance, is not so likely because a giraffe has hardly any enemies. With one kick of his large hooves he can kill a lion, so they leave the giraffe alone. Like the explanation of the acacia tree or the necking, this is an explanation of one cause and one phenomenon, whereas - compared to his ancestors - the giraffe has changed many characteristics at the same time.

As Stephen Jay Gould writes, "the giraffe's neck cannot provide a proof for any adaptive scenario, Darwinian or otherwise." An explanation should include all of the features: the long (but still too short) neck, the long legs, the large hooves, the long jaw, the long tongue, the big eyes, the short, upright horns and more.

Left: two male giraffe, necking. Right: possible ancestors of the giraffe.

Coincidence or not?

That evolution has taken place and species come and go, seems to be beyond doubt. The question is, whether it was as Darwin described; whether species adapt to the environment and evolution is blind. Or whether change comes from within and there is a direction that leads to higher developed species and ultimately to man. Biologists like Kim Meijer (Groningen University) have no doubt:

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Charles Darwin

Speciation: from one population a new species emerges caused by a geographical barrier

An apple maggot

A cinnabar moth

A monarch butterfly

Giraf etend van lage struiken
Drinkende giraf
Giraffen slaan elkaar met de nek

In the dry season the giraffe feeds on low shrubs.

A giraffe needs to put its front legs wide apart to
be able to graze or drink, otherwise its neck is too short to reach the ground. Observe the long, slender head.

A dolphin

A swallowtail

A hummingbird

An orchid