Toefl integrated writing task.

Hi, I'm taking the TOEFL ibt test in a few weeks. Could somebody have a look at my response?
I think I have mentioned all the essential information; however, I'm not sure about my grammar and sentence structure.

In this set of materials, the reading passage describes altruism and gives a few examples of it. The listening passage casts doubt on the reading passage by contradicting some information given in the reading passage.
The reading passage describes altruism as an unselfish act where one animal sacrifices its own interest for another animal or group of animals. It can be a donation of body organs for other‘s good. Also, an example of meerkats is given. An individual of these mammals tends to stand as a guard while others eat. By standing as a guard the individual gains nothing for itself. In fact, it only places itself in danger.
The listening passage confronts the information in the reading passage. A recent study mentioned in the listening passage has shown that meerkats eat before standing as guards and that those who stand as guards are most likely to escape if a certain predator appears. Therefore, their behavior is not altruistic as it was stated in the reading article. The listening section also discusses people‘s altruism. An example is given of a person who donates his kidney. The person might do that because he receives appreciation from public, also his self-appreciation increases and this is not related to altruism.

As you see, I have marked some words. My inquiry: Is it appropriate to use the male gender if I am not sure whether the person is a man or not. In my native language each word has its own gender but English is quite different.

THANKS A LOT!!!