The Human Seed

وَهُوَ الَّذِي يُرْسِلُ الرِّيَاحَ بُشْرًا بَيْنَ يَدَيْ رَحْمَتِهِ ۖ حَتَّىٰ إِذَا أَقَلَّتْ سَحَابًا ثِقَالًا سُقْنَاهُ لِبَلَدٍ مَيِّتٍ فَأَنْزَلْنَا بِهِ الْمَاءَ فَأَخْرَجْنَا بِهِ مِنْ كُلِّ الثَّمَرَاتِ ۚ كَذَٰلِكَ نُخْرِجُ الْمَوْتَىٰ لَعَلَّكُمْ تَذَكَّرُونَ

And it is He who sends the winds as good tidings before His mercy until, when they have carried heavy rainclouds, We drive them to a dead land and We send down rain therein and bring forth thereby [some] of all the fruits. Thus will We bring forth the dead; perhaps you may be reminded. (7:57)

Allah states in other places in the Quran:

So observe the effects of the mercy of Allah - how He gives life to the earth after its lifelessness. Indeed, that [same one] will give life to the dead, and He is over all things competent. (30:50)

And We have sent down blessed rain from the sky and made grow thereby gardens and grain from the harvest, And lofty palm trees having fruit arranged in layers - As provision for the servants, and We have given life thereby to a dead land. Thus is the resurrection. (50:9-11)

A few Hadith elaborate on the matter:

Narrated Al-A`mash:
Abu Huraira said, "Allah's Apostle said, 'Between the two sounds of the trumpet, there will be forty." Somebody asked Abu Huraira, "Forty days?" But he refused to reply. Then he asked, "Forty months?" He refused to reply. Then he asked, "Forty years?" Again, he refused to reply. Abu Huraira added. "Then (after this period) Allah will send water from the sky and then the dead bodies will grow like vegetation grows, There is nothing of the human body that does not decay except one bone; that is the little bone at the end of the coccyx of which the human body will be recreated on the Day of Resurrection." [Bukhari]

Abu Huraira reported Allah's Messenger (may peace be upon him) as saying:
Between the two blowings of the trumpet (there would be an interval of forty). They said: Abu Huraira, do you mean forty days? He said: I cannot say anything. They said: Do you mean forty months? He said: I cannot say anything They said: Do you mean forty years? He said: I cannot say anything. Then Allah would cause the water to, descend from the sky and they (people) will sprout like vegetable The only thing in a man which would not decay would be one bone (spinal chord) from which the whole frame would be reconstituted on the Day of Resurrection. [Muslim]

Allah states that just as He brings life to dead land, He shall raise up the dead on the Day of Resurrection, after they have disintegrated. Allah will send down rain from the sky and the rain will pour on the earth for forty days. The corpses will then be brought up in their graves, just as the seeds grow in the ground (on receiving rain). Allah often mentions this similarity in the Qur'an when He gives the example of what will happen on the Day of Resurrection, and bringing life to dead land," so that  لَعَلَّكُمْ تَذَكَّرُونَ "perhaps you may be reminded." [1]

On the Last Day humans will be formed from a small bone. When the water reaches this bone, the body will grow from it like an herb grows out of a seed. This bone is the coccyx (tailbone) which is a round bone at the base of the spine.

What is also interesting is the word usage.  Allah used the verb أَخْرَجَ Akhraja, roughly translated as 'to bring forth', to resurrect the human (7:57).  He also used the same verb when He talks about 'bringing forth' plants from the dead earth after rainfall (32:37), and when He 'brings forth' people from the wombs of their mothers (16:78). [2]

Each type of 'bringing forth' starts with a seed.  The coccyx being the seed for resurrection, the plant seed for the plants, and the egg for the developing human in the womb.

[1] Tafsir Ibn Kathir
[2] Muhammad Abdul Haleem (2001), Understanding The Quran: Themes and Styles. London: I.B Tauris & Co Ltd. pp39.