Human Influence on Natural Selection

In this science blog we look at the role humans play in influencing the evolution of animals through ‘artificial’ selection.

Differences between ‘natural’ and ‘artificial’ selection

There is one main difference between ‘natural’ and ‘artificial’ selection.

With natural selection the ‘good’ features of evolution allow an animal to adapt, survive and reproduce in its natural habitat.

With artificial selection it is the human breeder who decides which features of an animal are ‘good’ and worthy of being passed onto the next generation. Those animals which evolve through artificial selection do not have to live in the wild and are dependent on humans for their food and survival.

  • Can you name any organisms that have evolved different physical characteristics through ‘artificial’ selection?

Yorkshire Terrier dressed in a coat and bow in hair

So we humans are able to sculpture and mould animals any way we want!

Four large Gromits with each Gromit painted in four different ways

 Charles Darwin and ‘selective breeding’

Portrait of Charles Darwin as a young manCharles Darwin was the English naturalist who is credited with first proposing the ‘theory’ of evolution by natural selection in his ground breaking book,’The Origin of the Species’,published in 1859.

The first chapter of ‘The Origin of the Species’ is entitled ‘Variation under Domestication’ and is all about selective artificial breeding.

Darwin describes how people have used ‘selective breeding’ to sculpt the appearance of different organisms such as pigeons, dogs and cabbages. In Darwin’s own words,’one of the most remarkable features in our domesticated races is that we see in them adaption, not indeed to the plant’s or animals’ own good, but to man’s use or fancy’.

Darwin includes evidence of ‘artificial breeding’ to try and persuade people of the merits of his ‘theory’ of evolution by natural selection. He knew that if people could accept the idea of artificial selection- whose success was obvious to all- then making the leap to understanding and believing the ‘theory’ of natural selection would not have been so very difficult.

In 1859 ‘evolution by natural selection’ was still very much a controversial ‘theory’ which was not destined to become mainstream scientific ‘fact’ for many years.

Today many people of religious faith still do not accept ‘evolution by natural selection’ as scientific fact because the science does not accord with their own religious convictions.

We will now look at some examples of ‘evolution by artificial selection’ as mentioned by Darwin in his book.

‘Variation under domestication’ – the pigeon.

All species of pigeon alive today are descended from one common ancestral species- the ‘rock dove’ (Columba livia) 

key stage 2 science-Rock pigeon standing at rest with wings folded

One species, the ‘English Pouter’ is artificially bred to have a large chest; those ‘English Pouters’ with the most impressive chests and longest legs win prizes at pigeon ‘beauty contests’!

English Pouter pigeon with distinctive protruding chest

Another species, the ‘Barb’ pigeon, wins prizes if it has impressive knobbly bits of flesh (‘ceres’) round its eyes.

English Barb pigeon with distinctive orange round eyes

Yet a further species, the ‘Fan Tail’ pigeon wins prizes if it has a pronounced chest and impressive tail feathers.

key stage 2 science-White fantail pigeons showing large chests and fancy tails

‘Variation under Domestication’- the cabbage

The ‘evolutionary pressures’ to artificially ‘sculpt’ cabbages was not so much to win prizes but to develop nutritious sources of food.

The wild cabbage (also called the wild ‘mustard’ plant) is the spindly and weedy looking ancestor of the domestic cabbage. Over the last 10 000 years using selective breeding techniques, farmers and horticulturalists have sculpted different species of cabbage that look strikingly different to their wild ancestors, as you can appreciate when you look at the image below:

illustration of wild cabbage showing decendants including broccoli and Brussels sprouts

‘Variation under Domestication’- the wolf

It has been proven beyond all doubt that all dogs living today are descended from the wolf. (Canis lupus)

three wolves howling against a backdrop of pine trees in the snow

It’s amazing to think that wolves, Great Danes and Chihuahuas are all so closely related!

Great Dane and Chihuahua looking at each other

The pace of dog ‘evolution by artifical selection’ has increased greatly over the past 150 years, with the emergence of dog shows such as Crufts which was first held in London in 1886.

Afghan hound looks like owners all of whom have long blond hair

Other examples of ‘evolution by artificial selection’

Leaving Charles Darwin to one side for now, two other examples of artificial selection are mentioned below:

The ‘Belgian Blue’ has been artificially ‘improved’ to provide large numbers of beef steaks!

belgian-blue-bullock

 

Cows have evolved large udders to provide us humans with copious quantities of milk. They produce far more milk than their calves ever need to consume.

dairy cow with large udders

Artificial selection (or not?)  – the curious case of the Heikea japonica

It is a historical fact that following the sea battle of Dan-no-ura (壇ノ浦の戦い ) off the coast of Japan in 1185, the defeated Heika general Taira no Tomomori (平 知盛) drowned himself by attaching himself to a ship’s anchor before throwing the anchor into the sea.

Many Samurai warriors drowned alongside him.

Popular legend would have us believe that the ghosts of the drowned warriors now inhabit the bodies of Heika japonica crabs; the very crabs that live on the sea floor in the exact spot where the warriors drowned.

The ghost of a Heika general at the bottom of the sea accompanied by Heika japonica crabs

 

The ghosts of those unfortunate warriors are still ‘alive’ today inhabiting the bodies of Heika japonica crabs. You can see their faces on the backs of all the H japonica crabs…

key stage 2 science-Heika japonica crab alongside a face of a samurai warrior for comparison purposes

Generations of Japanese fishermen, through artificial selection, are responsible for the fact that the Heika japonica crabs have developed ‘ghost faces’ on their exterior shells.(‘carapaces’)

Whenever fishermen catch any crab that bears the slightest resemblance to a human face it is quickly released back into the sea; no fisherman wants to kill a ‘ghost warrior’!

Those crabs that do not have faces resembling Samurai warriors are cooked and eaten.

three medieval japanese fishermen in boat, two with oars and one fishing with a net

Over hundreds of years through ‘artificial selection’ crabs have developed faces that look even more ‘human like’. Facial characteristics have become evolutionarily fixed in the wider population of Heika japonica crabs.

Sceptics who do not believe that fishermen are responsible for creating ‘warrior faces’ on the backs of these crabs through artificial selection. They maintain that the H japonica is too small to be eaten and that all crabs of this size would have been thrown back into the sea, whether or not their backs resemble human faces. In any case, the grooves in the crabs’ backs mark nothing more than muscle attachments underneath the crabs’ shells.dog howling and pretending to be a wolf

  • Fact or fiction? You decide!

Science fair projects

  • Investigate different breeds of ‘fancy pigeons’.
  • Investigate different breeds of dog at Animal.Discovery.com. What physical characteristics of dogs have humans altered through ‘artificial’ selection?
  • Investigate other organisms that have been modified by humans using ‘artificial’ selection.
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