A huge marine mammal known as Steller’s sea cow once lived in the waters around Bering Island off the coast of Siberia. It was described in 1741 by Georg W. Steller, a naturalist who was among the first Europeans to see one. In 1768 the animal became extinct. The reasons for the extinction are not clear. Here are three theories about the main cause of the extinction.
First, the sea cows may have been overhunted by groups of native Siberian people. If this theory is correct, then the sea cow population would have originally been quite large, but hundreds of years off too much hunting by the native people diminished the number of sea cows. Sea cows were a good source of food in a harsh environment, so overhunting by native people could have been the main cause of extinction.
Second, the sea cow population may have become extinct because of ecosystems disturbances that caused a decline in their main source of food, kelp (a type of sea plant). Kelp populations respond negatively to a number of ecological changes. It is possible that ecological changes near Bering Island some time before 1768 caused a decrease of the kelp that the sea cows depend on.
Third, the main cause of extinction of the sea cows could have been European fur traders who came to the island after 1741. It is recorded that the fur traders caught the last sea cow in 1768. It thus seems reasonable to believe that hunting by European fur traders, who possessed weapons that allowed them to quickly kill a large number of the animals, was the main cause of the sea cow’s extinction.
The professor disagrees with the notion in the text about three hypotheses that explains the sea cow's extinction. He brings several reasons to support his idea.
First, the lecturer mentions that sea cows were enormous animal that each of them could provide large amount of food for native Siberian people. As a result, Siberian people did not need to hunt a great deal of sea cows in order to prepare a food for themselves. In contrast, the reading claims that sea cows extincted by over-hunting of Siberian people. Actually, the author of the text believe that Siberian people hunted many sea cows so as to meet their food need.
Second, the speaker specifies that Kelp populations was not reduced on that time because if Kelp populations was decreased we should see that other marine animals such as whale were died but we do not have any reports to indicates this fact. Consequently, the numbers of Kelp was considerable on that time therefore sea cows were able to eat them. Hence, the extinction is not related to the Kelp populations. However, the article states that Kelp was the main source of food for sea cows therefore when the numbers of Kelp were reduced, the sea cows did not have any food sources to use so they died.
Finally, the instructor hints that, before the European traders arrived to the island, the numbers of sea cows were declined. Thus, we cannot conclude that the fur traders had notable impacts on the extinction of sea cows. On the other hand, according to the reading, European fur traders kill a lot of sea cows by their weapons. Thereby, hunting by traders contributed to the sea cow's extinction.
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Grammar and spelling errors:
Line 1, column 98, Rule ID: POSSESIVE_APOSTROPHE[2]
Message: Possible typo: apostrophe is missing. Did you mean 'cows'' or 'cow's'?
Suggestion: cows'; cow's
... three hypotheses that explains the sea cows extinction. He brings several reasons t...
^^^^
Line 3, column 178, Rule ID: WHITESPACE_RULE
Message: Possible typo: you repeated a whitespace
Suggestion:
...people. As a result, Siberian people did not need to hunt a great deal of sea cow...
^^
Line 3, column 242, Rule ID: A_UNCOUNTABLE[1]
Message: Uncountable nouns are usually not used with an indefinite article. Use simply 'food'.
Suggestion: food
...at deal of sea cows in order to prepare a food for themselves. In contrast, the readin...
^^^^^^
Line 3, column 440, Rule ID: SO_AS_TO[1]
Message: Use simply 'to'
Suggestion: to
...at Siberian people hunted many sea cows so as to meet their food need. Second, the sp...
^^^^^^^^
Line 7, column 382, Rule ID: POSSESIVE_APOSTROPHE[2]
Message: Possible typo: apostrophe is missing. Did you mean 'cows'' or 'cow's'?
Suggestion: cows'; cow's
...nting by traders contributed to the sea cows extinction.
^^^^
Transition Words or Phrases used:
actually, but, consequently, finally, first, hence, however, if, second, so, therefore, thus, as to, in contrast, such as, as a result, on the other hand
Attributes: Values AverageValues Percentages(Values/AverageValues)% => Comments
Performance on Part of Speech:
To be verbs : 10.0 10.4613686534 96% => OK
Auxiliary verbs: 5.0 5.04856512141 99% => OK
Conjunction : 1.0 7.30242825607 14% => More conjunction wanted.
Relative clauses : 13.0 12.0772626932 108% => OK
Pronoun: 24.0 22.412803532 107% => OK
Preposition: 36.0 30.3222958057 119% => OK
Nominalization: 4.0 5.01324503311 80% => OK
Performance on vocabulary words:
No of characters: 1359.0 1373.03311258 99% => OK
No of words: 283.0 270.72406181 105% => OK
Chars per words: 4.80212014134 5.08290768461 94% => OK
Fourth root words length: 4.10153676581 4.04702891845 101% => OK
Word Length SD: 2.4978158497 2.5805825403 97% => OK
Unique words: 148.0 145.348785872 102% => OK
Unique words percentage: 0.52296819788 0.540411800872 97% => OK
syllable_count: 411.3 419.366225166 98% => OK
avg_syllables_per_word: 1.5 1.55342163355 97% => OK
A sentence (or a clause, phrase) starts by:
Pronoun: 2.0 3.25607064018 61% => OK
Interrogative: 0.0 0.116997792494 0% => OK
Article: 11.0 8.23620309051 134% => OK
Subordination: 2.0 1.25165562914 160% => OK
Conjunction: 0.0 1.51434878587 0% => OK
Preposition: 4.0 2.5761589404 155% => OK
Performance on sentences:
How many sentences: 14.0 13.0662251656 107% => OK
Sentence length: 20.0 21.2450331126 94% => OK
Sentence length SD: 49.0666456392 49.2860985944 100% => OK
Chars per sentence: 97.0714285714 110.228320801 88% => OK
Words per sentence: 20.2142857143 21.698381199 93% => OK
Discourse Markers: 10.9285714286 7.06452816374 155% => OK
Paragraphs: 4.0 4.09492273731 98% => OK
Language errors: 5.0 4.19205298013 119% => OK
Sentences with positive sentiment : 2.0 4.33554083885 46% => More positive sentences wanted.
Sentences with negative sentiment : 4.0 4.45695364238 90% => OK
Sentences with neutral sentiment: 8.0 4.27373068433 187% => OK
What are sentences with positive/Negative/neutral sentiment?
Coherence and Cohesion:
Essay topic to essay body coherence: 0.159396232565 0.272083759551 59% => OK
Sentence topic coherence: 0.0593119756106 0.0996497079465 60% => OK
Sentence topic coherence SD: 0.0331243055943 0.0662205650399 50% => OK
Paragraph topic coherence: 0.0889605824479 0.162205337803 55% => OK
Paragraph topic coherence SD: 0.0323311681313 0.0443174109184 73% => OK
Essay readability:
automated_readability_index: 11.3 13.3589403974 85% => Automated_readability_index is low.
flesch_reading_ease: 59.64 53.8541721854 111% => OK
smog_index: 3.1 5.55761589404 56% => Smog_index is low.
flesch_kincaid_grade: 9.9 11.0289183223 90% => OK
coleman_liau_index: 10.56 12.2367328918 86% => OK
dale_chall_readability_score: 7.92 8.42419426049 94% => OK
difficult_words: 59.0 63.6247240618 93% => OK
linsear_write_formula: 7.5 10.7273730684 70% => OK
gunning_fog: 10.0 10.498013245 95% => OK
text_standard: 10.0 11.2008830022 89% => OK
What are above readability scores?
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Rates: 80.0 out of 100
Scores by essay e-grader: 24.0 Out of 30
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Note: the e-grader does NOT examine the meaning of words and ideas. VIP users will receive further evaluations by advanced module of e-grader and human graders.