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Natural Environment How Human History has been impacted by the environment, science, nature, geography, weather, and natural phenomena


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Old August 5th, 2012, 06:51 AM   #1

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Samurai crabs: human driven evolution


I wasn't sure where to put this, as it combines both Japanese history and the natural environment, but this seems to be the best choice.

Some of you may be familiar with the story of the Heike crabs - they were featured on an episode of Cosmos by the late, great Carl Sagan.

The naval battle of Dan-no-Ura took place in 1185, and was the culmination of the Gempei War in which the Taira clan (also known as the Heike) and the Minamoto clan (also known as the Genji) fought for control of Japan. It was fought in the Shimonoseki Strait, between the two main Japanese islands of Honshu and Kyushu. Although the Taira had the initial advantage, a change in the tides and a defection by a Taira general turned the battle in favour of the Minamoto. Seeing the battle lost, many Taira samurai threw themselves overboard and drowned, rather than be captured by their mortal enemies - the dead included the eight-year old child-emperor Antoku and his grandmother.
Battle of Dan-no-ura - Wikipedia, the free encyclopedia

In the years following the battle, the local fisherman began to notice some crabs with what looked like distorted faces on their shells. These crabs were said to hold the spirits of the deceased Taira samurai, so they were thrown back into the sea and not eaten. These crabs would survive to pass on their genes (and their face-like shells) to their descendents, and their higher survival rate has led to all the crabs (known as Heikigani in Japanese, Heikeopsis japonica) having faces on their shells. This is a picture of a Heike crab:
Click the image to open in full size.
Heikegani Heikegani

Sagan's theory is not universally accepted, as noted in the article above.

I hope you found this interesting!
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Old August 5th, 2012, 06:58 AM   #2

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An example of human-driven behavioural modification in wild animals can also be found in Japan. The deer of Nara, which I have mentioned on this board before, are considered sacred and messengers of the god Takemikazuchi. Thus, the deer are left to roam freely throughout Nara national park and also through the city itself. They are not tame.

You can buy crackers (shika senbei, deer crackers) to feed them, and the deer have completely lost their fear of humans. They are famously mercenary and have learned all sorts of tricks such as stepping on your foot to stop you retreating if they know you have crackers to feed them. They also gather around vendors to keep a beady eye on any tourists buying the crackers. Larger deer will mercilessly headbutt smaller and younger deer away when crowding around you for crackers. Bambi, they ain't.

But the specific example of learned behaviour is the bowing. Bowing is, of course, a major part of Japanese etiquette, and the deer have noticed that nodding their heads in response to a human's bow tends to get them fed. The deer have learned this behaviour entirely of their own accord, and have not been trained to do it:

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Old August 5th, 2012, 08:02 AM   #3
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I wouldn't have known the Battle of Dannoura and the Samurai crabs if I haven't seen Kwaidan.

That bowing dear is pretty interesting...and unsettling.
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Old August 5th, 2012, 08:15 AM   #4

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I remember seeing that episode of the Samurai crabs and found
it a fascinating tale. Thanks for jarring my memory over it again.
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Old August 5th, 2012, 09:09 AM   #5

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They say that Samurai Crabs can jump six feet!
Or am I getting this mixed up with something else?
Either way, a broad spectrum antibiotic will probably clear it up.
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Old August 5th, 2012, 05:57 PM   #6

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If Sagan's theory is correct it is an example of selective breeding, not evolution.
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Old August 6th, 2012, 01:28 AM   #7

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Ah, Japan. Is there anything about you that isn't crazy?
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Old August 6th, 2012, 01:38 AM   #8
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Theres a similar case with moths in the UK.

The wikki artical is more detailed
Peppered_moth_evolution Peppered_moth_evolution

Essentially the Peppered Moth came in two colours Black and White. The Black moths stood out against the white tree bark and were easy prey and as a result were quite rare. Come the industrial revolution the trees were stained black by soot and now it was the white moths who stood out and became easy pray, and they became quite rare. After pollution controll was put in the trees were no longer covered in soot and the Black moths became quite rare.


Click the image to open in full size.

Both a black and white moth are in this photo, the white moth is almost invisable, it is so well camoflaged.
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