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Well I have noticed that almost all of the babies cry after birth, but some of them (1 to 1,000,000? births) don't cry. So, we have:

  1. Why is this happening (the cry after birth)?

  2. Also why animals babies don't cry when they are born, but human babies cry? I have noticed that many mammals such as giraffes or chimps don't cry at all (The chimp only makes it's ordinary sounds).

  3. Are there any special genes that humans have and animals not?

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    $\begingroup$ Lots of baby animals "cry" after they are born, everything from puppies to calves often vocalize when born $\endgroup$ – Harry Vervet Jan 8 '17 at 14:18
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    $\begingroup$ Crying keeps lungs dry by increasing alveolar air pressure, which otherwise is fatal. $\endgroup$ – JM97 Jan 8 '17 at 14:23
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    $\begingroup$ I don't know if you have ever witnessed one, but childbirth is a rather extreme and violent expierence, were the child is pushed through something that is a bit to small for its head. That alone would be reason enough to cry. And crying has indeed a function for the lungs, as explained by JM97 $\endgroup$ – RHA Jan 8 '17 at 19:41
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    $\begingroup$ Having delivered at least a hundred babies, I guarantee you that your statistic is wrong. As long as the baby is breathing, the fluid in the lungs will be resorbed. Still, usually they are cold and wet and under bright lights when delivered. The more you mitigate this harsh new environment, the more peaceful the birth can be. Some babies don't cry at all. If everything else is ok (color, muscle tone, heart rate, etc.), it's no biggie. $\endgroup$ – anongoodnurse Jan 9 '17 at 3:58
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    $\begingroup$ So, you believe that they cry because of that change? $\endgroup$ – The_Mad_Fish Jan 9 '17 at 7:37
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I'm answering this question (mostly) based on prior knowledge.

Inside the womb, the foetus relies on the mother for oxygen i.e. it receives oxygen from the mother's bloodstream via the umbilical cord. A foetus doesn't use its lungs for breathing inside the womb. Ever.

Besides, lungs of a foetus are considered fully matured no earlier than the 36th week of pregnancy. (Though there are exceptions to this)

During fetal life the baby's lungs are filled with fluid and they do not perform any respiratory functions. [1]

At birth, the baby is forced to breath on its own for the first time. Hence, the baby cries - or more precisely - gasps for air. This 'cry' of the baby is actually a strong respiratory effort, thereby aiding the baby in its first breath. This is also why newborns don't produce tears on their first cry. Because it's not really a cry, it's a gasp for air.

Now the reason why such a considerable effort is required for the newborn to breathe is because:

A) Lungs are being used for the first time, and

B) The lungs of a foetus are filled with amniotic fluid when it's inside the womb. Effort is needed to push this fluid out from the lungs after birth.

I'm not aware if there's any genetics involved in this. I don't think there is.

Source: [1] http://www.thehindu.com/todays-paper/tp-features/tp-sci-tech-and-agri/babys-first-cry/article2267767.ece

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I don't disagree with answers that talk about lung function. But a scream would do the same thing. About whether humans are unique, in terms of care they are among the most helpless of animals. Crying in babies is a form of communication that calls the parents into action when care is needed. In the first moments of life in the light and air, besides the shock of being squeezed through an opening so small that the skull is squeezed into a different shape (ouch), an infant urgently needs care.

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