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.
Both the reading passage and the lecture discuss about the possible causes of the extinction of the Steller's sea cow. The passage proposes three theories that could possibly explain the extinction. However, the professor in the lecture casts doubt on all the theories mentioned in the passage.
First of all, the passage claims that the sea cows may have been over-hunted by groups of native Siberian people, since they were a good source of food in a harsh environment. Nevertheless, the professor questions the passage by arguing that the sea cow is a massive creature, which are large and heavy. Few couples of the sea cows could feed all of the native Siberian people for months. Thus, it is unlikely that they over-hunted the sea cows.
Secondly, the passage mentions that ecosystem disturbances could be another possible cause. Because the ecosystem disturbances caused a decline in the kelp, which is one of food source that the sea cow feed on. Notwithstanding, the professor disagrees with the passage. Instead, he claims that ecosystem disturbances would affect other parts of the ecosystem, such as whales, yet there was no report about the decline of whale's population. Hence, this theory is not convincing.
Finally, the passage suggests that the main cause of extinction of the sea cows could have been European fur traders, who possessed weapons that allowed them to quickly kill a large number of the animals. However, the professor refutes the passage by pointing out that by the time that they arrived, the population of the sea cow was already small. Moreover, there is evidence indicates that the sea cow's population had decreased before 1741.
Grammar and spelling errors:
Line 1, column 160, Rule ID: MAY_COULD_POSSIBLY[1]
Message: Use simply 'could'.
Suggestion: could
...he passage proposes three theories that could possibly explain the extinction. However, the pr...
^^^^^^^^^^^^^^
Line 3, column 344, Rule ID: ALL_OF_THE[1]
Message: Simply use 'all the'.
Suggestion: all the
... Few couples of the sea cows could feed all of the native Siberian people for months. Thus...
^^^^^^^^^^
Line 7, column 175, Rule ID: LARGE_NUMBER_OF[1]
Message: Specify a number, remove phrase, or simply use 'many' or 'numerous'
Suggestion: many; numerous
...apons that allowed them to quickly kill a large number of the animals. However, the professor ref...
^^^^^^^^^^^^^^^^^
Line 7, column 401, Rule ID: POSSESIVE_APOSTROPHE[1]
Message: Possible typo: apostrophe is missing. Did you mean 'cows'' or 'cow's'?
Suggestion: cows'; cow's
...here is evidence indicates that the sea cows population had decreased before 1741.
^^^^
Transition Words or Phrases used:
finally, first, hence, however, may, moreover, nevertheless, second, secondly, so, thus, such as, first of all
Attributes: Values AverageValues Percentages(Values/AverageValues)% => Comments
Performance on Part of Speech:
To be verbs : 12.0 10.4613686534 115% => OK
Auxiliary verbs: 6.0 5.04856512141 119% => OK
Conjunction : 3.0 7.30242825607 41% => More conjunction wanted.
Relative clauses : 15.0 12.0772626932 124% => OK
Pronoun: 19.0 22.412803532 85% => OK
Preposition: 33.0 30.3222958057 109% => OK
Nominalization: 8.0 5.01324503311 160% => OK
Performance on vocabulary words:
No of characters: 1399.0 1373.03311258 102% => OK
No of words: 274.0 270.72406181 101% => OK
Chars per words: 5.10583941606 5.08290768461 100% => OK
Fourth root words length: 4.0685311056 4.04702891845 101% => OK
Word Length SD: 2.68677842493 2.5805825403 104% => OK
Unique words: 145.0 145.348785872 100% => OK
Unique words percentage: 0.529197080292 0.540411800872 98% => OK
syllable_count: 423.9 419.366225166 101% => OK
avg_syllables_per_word: 1.5 1.55342163355 97% => OK
A sentence (or a clause, phrase) starts by:
Pronoun: 3.0 3.25607064018 92% => OK
Article: 9.0 8.23620309051 109% => OK
Subordination: 2.0 1.25165562914 160% => OK
Conjunction: 1.0 1.51434878587 66% => OK
Preposition: 1.0 2.5761589404 39% => More preposition wanted as sentence beginning.
Performance on sentences:
How many sentences: 15.0 13.0662251656 115% => OK
Sentence length: 18.0 21.2450331126 85% => The Avg. Sentence Length is relatively short.
Sentence length SD: 45.8206164176 49.2860985944 93% => OK
Chars per sentence: 93.2666666667 110.228320801 85% => OK
Words per sentence: 18.2666666667 21.698381199 84% => OK
Discourse Markers: 7.33333333333 7.06452816374 104% => OK
Paragraphs: 4.0 4.09492273731 98% => OK
Language errors: 4.0 4.19205298013 95% => OK
Sentences with positive sentiment : 0.0 4.33554083885 0% => More positive sentences wanted.
Sentences with negative sentiment : 8.0 4.45695364238 179% => OK
Sentences with neutral sentiment: 7.0 4.27373068433 164% => OK
What are sentences with positive/Negative/neutral sentiment?
Coherence and Cohesion:
Essay topic to essay body coherence: 0.142471774339 0.272083759551 52% => OK
Sentence topic coherence: 0.0473969138881 0.0996497079465 48% => OK
Sentence topic coherence SD: 0.0418910016694 0.0662205650399 63% => OK
Paragraph topic coherence: 0.0879086536512 0.162205337803 54% => OK
Paragraph topic coherence SD: 0.0353544948385 0.0443174109184 80% => OK
Essay readability:
automated_readability_index: 11.8 13.3589403974 88% => Automated_readability_index is low.
flesch_reading_ease: 61.67 53.8541721854 115% => OK
smog_index: 8.8 5.55761589404 158% => OK
flesch_kincaid_grade: 9.1 11.0289183223 83% => OK
coleman_liau_index: 12.36 12.2367328918 101% => OK
dale_chall_readability_score: 7.99 8.42419426049 95% => OK
difficult_words: 60.0 63.6247240618 94% => OK
linsear_write_formula: 10.5 10.7273730684 98% => OK
gunning_fog: 9.2 10.498013245 88% => OK
text_standard: 9.0 11.2008830022 80% => OK
What are above readability scores?
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Rates: 81.6666666667 out of 100
Scores by essay e-grader: 24.5 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.