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 of 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 ecosystem 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 depended 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.
In the reading material, three theories are proposed to explain the extinction of the sea cows. The lecturer, however, hold a divergent attitude. He argues that there are problems with these explanations which can not be the main cause of the sea cow's extinction. Through relevant reasons and example, the lecturer refutes the hypotheses mentioned in the reading passage, and aptly substantiates his own viewpoints.
First of all, the lecturer points out that the Steller's sea cow has a massive body which is about 9 meters long and 10 ponds weight. A couple of sea cows can feed the native Siberian people for months. Since the population of the Siberian people is not very large, it is unlikely that their hunting behavior can cause the extinction of the sea cows.
Second, the lecturer suggests that no evidence can support the ecosystem disturbance hypothesis. If there are ecosystem disturbances during that period, the number other marine animals will also decrease, such as whales. However, there are no reports can indicate such a decline in other marine animals. This further refutes the theory mentioned in the reading passage.
Finally, the lecturer argues that the number of the sea cow is relative small at the time when European fur traders arrived. It indicates that the population of the sea cows starts to decline along before the arrival of European fur traders. which directly contradicts to the hypothesis maintained in the reading passage.
Grammar and spelling errors:
Line 7, column 243, Rule ID: UPPERCASE_SENTENCE_START
Message: This sentence does not start with an uppercase letter
Suggestion: Which
...re the arrival of European fur traders. which directly contradicts to the hypothesis ...
^^^^^
Line 7, column 243, Rule ID: SENTENCE_FRAGMENT[1]
Message: “which” at the beginning of a sentence requires a 2nd clause. Maybe a comma, question or exclamation mark is missing, or the sentence is incomplete and should be joined with the following sentence.
...re the arrival of European fur traders. which directly contradicts to the hypothesis ...
^^^^^
Transition Words or Phrases used:
also, finally, first, however, if, second, so, such as, first of all
Attributes: Values AverageValues Percentages(Values/AverageValues)% => Comments
Performance on Part of Speech:
To be verbs : 9.0 10.4613686534 86% => OK
Auxiliary verbs: 6.0 5.04856512141 119% => OK
Conjunction : 3.0 7.30242825607 41% => More conjunction wanted.
Relative clauses : 11.0 12.0772626932 91% => OK
Pronoun: 14.0 22.412803532 62% => OK
Preposition: 26.0 30.3222958057 86% => OK
Nominalization: 7.0 5.01324503311 140% => OK
Performance on vocabulary words:
No of characters: 1231.0 1373.03311258 90% => OK
No of words: 239.0 270.72406181 88% => More content wanted.
Chars per words: 5.15062761506 5.08290768461 101% => OK
Fourth root words length: 3.93187294222 4.04702891845 97% => OK
Word Length SD: 2.65253487207 2.5805825403 103% => OK
Unique words: 134.0 145.348785872 92% => More unique words wanted.
Unique words percentage: 0.560669456067 0.540411800872 104% => OK
syllable_count: 381.6 419.366225166 91% => OK
avg_syllables_per_word: 1.6 1.55342163355 103% => OK
A sentence (or a clause, phrase) starts by:
Pronoun: 4.0 3.25607064018 123% => OK
Article: 7.0 8.23620309051 85% => OK
Subordination: 2.0 1.25165562914 160% => OK
Conjunction: 1.0 1.51434878587 66% => OK
Preposition: 3.0 2.5761589404 116% => OK
Performance on sentences:
How many sentences: 14.0 13.0662251656 107% => OK
Sentence length: 17.0 21.2450331126 80% => The Avg. Sentence Length is relatively short.
Sentence length SD: 30.4744791186 49.2860985944 62% => OK
Chars per sentence: 87.9285714286 110.228320801 80% => OK
Words per sentence: 17.0714285714 21.698381199 79% => OK
Discourse Markers: 4.85714285714 7.06452816374 69% => OK
Paragraphs: 4.0 4.09492273731 98% => OK
Language errors: 2.0 4.19205298013 48% => OK
Sentences with positive sentiment : 0.0 4.33554083885 0% => More positive sentences wanted.
Sentences with negative sentiment : 6.0 4.45695364238 135% => 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: 0.119088754244 0.272083759551 44% => OK
Sentence topic coherence: 0.0388667424123 0.0996497079465 39% => Sentence topic similarity is low.
Sentence topic coherence SD: 0.0344130533063 0.0662205650399 52% => OK
Paragraph topic coherence: 0.0713962062208 0.162205337803 44% => OK
Paragraph topic coherence SD: 0.0305517257831 0.0443174109184 69% => OK
Essay readability:
automated_readability_index: 11.4 13.3589403974 85% => Automated_readability_index is low.
flesch_reading_ease: 54.22 53.8541721854 101% => OK
smog_index: 3.1 5.55761589404 56% => Smog_index is low.
flesch_kincaid_grade: 9.9 11.0289183223 90% => OK
coleman_liau_index: 12.29 12.2367328918 100% => OK
dale_chall_readability_score: 8.77 8.42419426049 104% => OK
difficult_words: 65.0 63.6247240618 102% => OK
linsear_write_formula: 8.0 10.7273730684 75% => OK
gunning_fog: 8.8 10.498013245 84% => OK
text_standard: 9.0 11.2008830022 80% => OK
What are above readability scores?
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Rates: 75.0 out of 100
Scores by essay e-grader: 22.5 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.