The females ovulate on average 5-15 eggs per cycle. Unfertilized eggs get reabsorbed and fertilized eggs start developing a shell. The shell takes 2 weeks to fully form. Once all the fertilized eggs have formed shells the female goes into a state very much like our labor except she is laying eggs, not giving birth to live young. Once the eggs are laid she puts them in her pouch to incubate for 2 months. Then after 2 months have passed, the eggs hatch and the baby aliens start drinking their mom's milk Their mom eats what is left of the eggs to recuperate. There can be up to 3 aliens in an egg while still being viable though this is rare.

My momma told me that if the aliens are the same size as humans or similar that their eggs would have to be as big as an ostrich egg.

Ostrich egg

Now that's big. But their pouch can accommodate. Their pouch is both secure and super elastic. And pouch skin shedding occurs separate from shedding the rest of the skin in fully grown aliens. Each time they shed skin from the pouch, it grows in actual size and is able to better hold the eggs.

Would each egg have to be as big as an ostrich egg when fully grown to keep proportions similar to human proportions(This is how come I thought an egg tract would not be enough)?


Here Is how my Momma came up with the ostrich egg size. She compared the alien egg to this: enter image description

A human baby in the womb, full term and the alien egg have the same size amniotic sac.

  • $\begingroup$ This is two questions at once and some of the background information is unnecessary. I suggest you ask these questions one at a time with only relevant information included. $\endgroup$ Nov 25, 2016 at 20:29
  • 1
    $\begingroup$ That edit looks good, removing the close vote - feel free to ask the other half as a separate question immediately, no need to wait. $\endgroup$
    – Tim B
    Nov 25, 2016 at 20:35

3 Answers 3


I took a different approach to ThreeLifes, in my case I am only assuming human proportions nothing else, so lets compare human numbers to ostriches.

Average Human Height & Weight:

Male: 1.76 m. & 88.68 kg. (5.775 ft. & 195.5 lbs)

Female: 1.62 m. & 73.57 kg. (5.27 ft. & 162.2 lbs)

Ostrich Height

Male: 2.1 - 2.8 m. (6.9 – 9.2 ft. & 250 lbs)

Female: 1.7 - 2.0 m. (5.6 – 6.6 ft. & 220 lbs)

Good news is that if your eggs are in scale, they would likely be smaller than an ostrich egg. Averaging out the numbers it would likely be 76% the size of an ostrich egg. So if an ostrich egg is 15 cm. (6 in.) in diameter and can weigh up to 1.36 kg. (3 lbs) then your alien eggs would likely be 13.9 cm. (5.48 in.) in diameter and weigh 1 kg. (2.3 lbs).

Pouch size

I had a hard time finding numbers on how much weight a kangaroo pouch can hold. I could only find uncited numbers like 3 kilograms (6.6 pounds). Which means your creature might be hurting if it tried to store all 15 eggs in one cycle. If it was a kangaroo it could hold 3 of your eggs, but it is your alien, you can make it bigger.

Growth cycle

Ostriches can lay 7 to 10 eggs vs your aliens 5 to 15. Those numbers with the sack size I would recommend dropping your egg numbers down slightly to 4 to 9 with anything greater than 9 eggs being statistical outliers (much like a human having octuplets).

Having 2 egg yokes in one egg is likely not going to result in even one baby, I would not even consider having triplets in one egg. Also note that intelligent species need more resources to grow and thus they will likely need every last bit of material in the egg.

Ostrich eggs take about 40 days to hatch, so having a 60 day from laying to hatch is completely reasonable from that perspective. However your creature is intelligent which at least one study blames our brains for delaying our growth rate because they are burning up so much energy. So your creature likely will have delayed learning capabilities compared to that of a human, since it will be diverting its fuel to physical growth and not brain power.


There is a quirk to human birth you should have present when thinking this question.
When apes are born, they are able to hang on to their mother's back in a matter of hours or days after the birth. Other mammal's babies are able to stand up and walk towards their mother's in search of mil on their own. This is specially so in mammals that give birth one baby at a time.
But humans have big heads, and so do their babies. A baby as developed as a new born ape would de the equivalent of a 18 month baby (don't quote me on this, i'm not a zoologist) and it's head would be too big for it's mother's birth canal.
That is why human's are born underdeveloped (neotenic, I think is the term), when they have all organs and limbs formed but while their heads are still small enough to get out.
Eggs, on the other hand, have no birth canal, they just break all around the baby when it hatches. So new born babies of a human sized egg-laying species may not have the same size of a human newborn.
That said, a human new born weighs about 3,2kg and measures about 40cm and an ostrich egg is about 1,5kg and 15cm, so:

Maybe an ostrich egg would be too small.


The baby aliens can be whatever size you want them to be. The final size they reach (adult alien size = adult human size) has very little bearing on what size the hatchlings are. A small offspring with a fast growth rate could become human-sized just as easily as (a) a big offspring with a slower growth rate or (b) a small offspring with a longer growth period.

Consider these creatures:

  • Ostrich egg hatches and becomes an ostrich sized adult. (Big baby, human sized adult).
  • Red kangaroo joey to adult (Tiny baby, human sized adult).
  • Sauropod dinosaur egg is about the same size as an ostrich egg, but becomes a 70 tonne titanosaur. (Big baby, enormously huge adult).
  • Giant squid eggs are teeny compared to ANY bird's eggs, but adult giant squid are much bigger than ostriches. (Tiny baby, huge adult).

So your mother alien could lay much smaller eggs, but have either:

  1. Babies which grow faster than a human child. A red kangaroo is adult (sexually mature) at 15 to 24 months old.
  2. Babies which grow at the same rate as a human, but just take an extra year to make up for starting off the size of a duckling, instead of the size of an ostrich chick.

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