Firstly, I'm not looking for an organism that gives birth to two separate species (like a human that gave birth to a human baby and a puppy) as I'm fairly sure that is impossible (though feel free to correct me if there is any example of that).

What I'm thinking is a symbiotic pairing that utilise the same egg (or seed, I'm happy for one half of the pairing to be a plant) to give birth to their young.

Obviously for an animal it would be easier if it was egg laying than mammalian with live births.

What I imagine is species one lays an egg or produces a seed and the second species either implants their own egg / seed into it or somehow absorbs the first egg / seed and grows it's own around it. I imagine the issue would be the first egg being damaged by the process, but I'm hoping it might still be possible.

So the question is, is something like that possible? Is there any example of it happening in real life?

  • $\begingroup$ Do you remember Alien 4? $\endgroup$ – Please_Dont_Bully_Me_SO_Lords Aug 21 '17 at 13:28
  • 2
    $\begingroup$ @PSyLoCKe I'm a bit of a wuss when it comes to anything scary so I've never seen any of the Alien movies, so no. $\endgroup$ – adaliabooks Aug 21 '17 at 13:30
  • $\begingroup$ I can think of parasitic examples, some which are really weird like ab orchid that is parsitical to a fungus that grows on it's seed, but not enough to give a real answer $\endgroup$ – Garret Gang Aug 21 '17 at 16:59
  • 3
    $\begingroup$ @Rab If they are of a different species, that's fine :) $\endgroup$ – adaliabooks Aug 21 '17 at 21:01
  • 7
    $\begingroup$ It is possible for an organism to birth individuals of two different species, for an appropriate definition of "species". E.g., edible frogs can produce offspring of their own species with pool frogs, or members of the marsh frog species with marsh frogs. There are also species complexes involving all-male species (e.g., among the cichlid fishes, IIRC) which produce more of their own members by mating with females of another species, which can reproduce more of their own kind with conspecific males. $\endgroup$ – Logan R. Kearsley Aug 21 '17 at 22:00

11 Answers 11


Mitochondria are responsible for allowing oxygen breathing in all Eukaryotes. Chloroplast are responsible for photosynthesis in plants.

They both carry their own DNA, it is thought they are symbiotic organism which managed to live and propagate inside a cell.

The establishment of the symbiosis took place really long time ago.

  • 1
    $\begingroup$ Mitochondria are found in plants, fungi, etc. ALL eukaryotes have them to produce cellular energy. Chloroplasts produce sugar (etc), not energy for the cell to use directly. $\endgroup$ – jaxad0127 Aug 21 '17 at 13:33
  • $\begingroup$ @jaxad0127, corrected the part about mitochondria. Chloroplast part I think it is correct, isn't it? Photosynthesis is the production of sugar starting from light and CO2 $\endgroup$ – L.Dutch - Reinstate Monica Aug 21 '17 at 13:42
  • $\begingroup$ As far as I know, yes. From what I remember from high school biology, photosynthesis actually takes a small amount of cellular energy. $\endgroup$ – jaxad0127 Aug 21 '17 at 13:53
  • 11
    $\begingroup$ Correction, mitochondria are not endosymbiotic organisms. This is uncontested. Rather, it's hypotethised that they originated that way evolutionarily. $\endgroup$ – Konrad Rudolph Aug 21 '17 at 13:57
  • 1
    $\begingroup$ Also, just noticed you said all aerobic organisms. Only eukaryotes have mitochondria. Bacteria and archaea use other methods. $\endgroup$ – jaxad0127 Aug 21 '17 at 14:00

Absolutely, it's possible.

Many, many, insects pass endosymbiotic bacteria in their eggs. The classical examples is Buchnera transmission in aphids, in which the symbiont is passed down the female line in the eggs.

  • 1
    $\begingroup$ This sounds interesting. Do you have a good source to read up on this? What is the reason for them to pass the symbionts only down the female line? $\endgroup$ – Sec SE - clear Monica's name Aug 21 '17 at 11:15
  • 3
    $\begingroup$ They're passed only down the female line because they are passed in the eggs, and not the sperm. This is likely due to sperm being too small to carry the endosymbiont. $\endgroup$ – Jack Aidley Aug 21 '17 at 11:16
  • 5
    $\begingroup$ @Secespitus Check out Wolbachia. $\endgroup$ – Mike Nichols Aug 21 '17 at 14:31
  • $\begingroup$ @MikeNichols "Some host species cannot reproduce, or even survive, without Wolbachia infection." Very interesting, thanks for the link $\endgroup$ – Sec SE - clear Monica's name Aug 21 '17 at 14:33

Portuguese man o' war

It's not a jellyfish it's a siphonophore, a colony organism.


There are dactylozoids, which make up the tentacles; there are gastrozoids, which are the bits that eat the food; and there are gonozoids, which are the bits of these creatures that reproduce. They produce sperm and eggs. In fact, you get female and male Portuguese man-o-war, even though they're called "Men"!

The sperm will fertilise eggs in the water column to produce larvae, which grow into bigger Portuguese man-o-wars.

The way that they grow from those individual cells is by asexual division of those cells and they produce all those individual three types of animals that live in this one colony and drift around the oceans, stinging things and eating things as they go.

  • $\begingroup$ This seems to be the closest to what I'm imagining so far, though it's fairly simple organisms. $\endgroup$ – adaliabooks Aug 21 '17 at 13:36
  • $\begingroup$ @adaliabooks, one would expect that more complex organisms had either moved beyond the need for symbiosis or had effectively merged into one organism. To get the two semi-independent symbiotic creatures you're apparently asking for would be unexpected. The closest equivalent might be the parasitic egg layers such as the cuckoo. $\endgroup$ – Separatrix Aug 21 '17 at 14:05
  • 1
    $\begingroup$ @Xen2050, I was trying to find that out but there's a general theme of "not entirely sure" going around. Note the lack of any mention of reproduction in wikipedia. $\endgroup$ – Separatrix Aug 21 '17 at 14:53
  • 12
    $\begingroup$ The Portuguese Man O' War is a colony organism, but every individual within the colony is genetically identical. It is one species with many different forms that live together. $\endgroup$ – Mike Nichols Aug 21 '17 at 16:14
  • 1
    $\begingroup$ The Portuguese man-o-war, and all other siphonophores are not true colonies as the individual zooids (parts of the organism) cannot survive on their own. Sorry to rain down on you but each zooid is not a different species. Like how there are different breeds of ant (Workers, Guards and Queens) but they are all the same species. Dogs are another example as a Border terrier can reproduce with a Dachshund. $\endgroup$ – Lucas O'connor Aug 24 '17 at 21:16

Yes it is possible. And in different ways:

I- Chloroplasts and Mitochondria. These two parts of the plant and animal cell respectively were once separate organisms. We know this because they both have their own D.N.A. In Animals the offspring receive mitochondrial D.N.A from the mother. This is not a separate organism though.

II- The spotted salamander. The spotted Salamander is photosynthetic. This is due a type of algae called Oophila amblystomatis. The organism is deeply intertwined with the salamander, even before birth. After the eggs have been laid and the embryo is developing it's nervous system if the algae is nearby it will travel into the egg. This is due to the fact that the egg releases nitrogen so the algae migrates to the food source. It will then eventually enter the developing tadpole's cells. Mitochondria will then spread around the algal cell. This gives the cells that contain the algae an extra source of oxygen and carbohydrate provided by the algae's photosynthesis.

A spotted salamander.

  • $\begingroup$ Nice answer, definitely a bit closer to what I was hoping as at least one of the species is a complex life form. $\endgroup$ – adaliabooks Aug 21 '17 at 21:01
  • 1
    $\begingroup$ Thank you. Also if this is for an SF story the algae could be replaced with small fish-like organisms that implant themselves with the embryo's tissue, since it is SF the idea could be further expanded on. $\endgroup$ – Lucas O'connor Aug 21 '17 at 21:30
  • $\begingroup$ “We know this because they both have their own D.N.A.” — To be precise, while the DNA is a strong hint, there are other possible explanations than endosymbiosis. For instance, it’s possible that the developed as organelles that caught viral DNA (or fragments of nuclear DNA) and made it their own. $\endgroup$ – Konrad Rudolph Aug 24 '17 at 12:17
  • $\begingroup$ Holy. Crap. Thanks for this answer, this is extremely cool and I've never heard of it before! $\endgroup$ – msouth Aug 24 '17 at 20:33

I cannot think of an example of a sexual reproduction mechanism which combines two symbionts in the same seed or egg; but many lichens, which are symbiotic associations of a fungus (the mycobiont) and an alga or a cyanobacteria (the photobiont), generate vegetative reproduction structures called soredia and isidia which carry propagules of both symbionts.

(A herbarium specimen of the lichen Leptogium cyanescens with lobule-shaped isidia. Photograph by Ed Uebel, available on Wikipedia under the CC-BY-SA-3.0 license.)

  • $\begingroup$ I think you may have a bad link, unless I'm misunderstanding the connection, the soredia link links to a wiki article about the Nephilim... $\endgroup$ – adaliabooks Aug 21 '17 at 13:35
  • $\begingroup$ @adaliabooks: Sorry, corrected. $\endgroup$ – AlexP Aug 21 '17 at 13:41

If two species are sharing the same egg, I think it would be easier for the sharing to start early on, before the egg of species one develops a hard shell - which would complicate any egg implanting mechanism like you mentioned in the question. For information on bird reproduction and egg formation see http://www.backyardnature.net/birdsex.htm

A possible process: (that I have invented)

  1. Species one male fertilises egg of species one female.
  2. Species two male fertilises egg of species two female.
  3. Soon after fertilisation, species two female "lays" egg into the oviduct of species one female.
  4. Species two egg is small soft and has a tail like a sperm, so it can swim up the oviduct and nestle into the species one egg yolk.
  5. Species one egg, now with species two egg inside, slowly moves down the oviduct and gets surrounded by egg white and then shell.
  6. Species one egg is laid.

Step 4) could be unreliable, so species two female should probably lay lots of eggs into species one female, to ensure there is a good chance that one successfully nestles into species one egg.


A healthy adult human has about a kilo of bacteria in/on them, mostly in the gut, and some of them help us digest food or reduce opportunities for other bacteria to harm us.

Some of them may get into us before we're born, coming from the mother's body via the placenta.1


Butterflies (and indeed all insects which undergo a complete metamorphosis) lay eggs which contain DNA with two different sets of instructions: one for the development of the caterpillar, and another for the development of the adult butterfly.

The original single cell starts to divide, creating a stock of stem cells. Some of these continue to divide and develop into the first instar caterpillar. The rest remain in a state of suspended development.

The caterpillar eats to build up body mass. It goes through four phases of development (instars), shedding its skin between each stage. Memories developed by one instar are passed on to the next*, but may not survive through to the following stage.

When the caterpillar is fully mature, it creates a chrysalid and the undifferentiated cells mentioned earlier start to divide and develop, consuming the "soup" from the caterpillar's body. Certain organs of the caterpillar are retained by the butterfly (eyes, parts of the legs, parts of the brain, ...) while others are destroyed and new ones (wings, antennae, ...) are created.

Adult butterflies often eat different plants from the caterpillars, and plants evolve in their own ways, so their consumers need to adapt to every change. So you have basically two different creatures, undergoing two different sets of evolutionary pressure, born from the same DNA in the same egg.


  • $\begingroup$ Hmmm, very interesting. That's probably a lot closer to what I'm thinking of than anything else so far +1 $\endgroup$ – adaliabooks Aug 24 '17 at 20:02

This is not a symbiote, but it provides an example of the principle. Chickens are relatively resistant to salmonella - the bacteria harms humans but not so much chickens. Eggs from an infected bird will be infected with salmonella because the bacteria are included in the fluids before the shell forms. There is no reason this principle could/does not apply to beneficial or symbiotic bacteria

  • 2
    $\begingroup$ Are chickens so resistant that most kill the salmonella with their immune systems? I note that many people ate raw eggs before we were taught to be afraid of them. I haven't eaten very many directly, but indirectly--My mother always let me (and my siblings lick the stirrers and bowls when she baked. $\endgroup$ – WGroleau Aug 21 '17 at 17:31
  • $\begingroup$ That is a good question. $\endgroup$ – pojo-guy Aug 21 '17 at 18:01
  • 1
    $\begingroup$ In the past people were more tolerant of diseases that did not kill compared to the blanket fear of everything. Not every egg is a vector. - Most people infected with Salmonella develop diarrhoea, fever, and abdominal cramps between 12 and 72 hours after infection. The illness usually lasts 4 to 7 days, and most individuals recover without treatment (US CDC) $\endgroup$ – KalleMP Aug 22 '17 at 18:15
  • $\begingroup$ Raw cookie dough does not pose significant salmonella risk according to most of the top hits on a google search about it. $\endgroup$ – msouth Aug 24 '17 at 20:50

Some species of coral spawn eggs with symbiotic algae already in the egg. (Other species gain their algae later in life). Scroll down to find some info in this article However corals and algae aren't the most dynamic and exciting of organisms! So not sure if that's what you are after.


Note the best example, but may help in your plot:

In Alien 4 movie, they were creating clones of the woman Ripley who as with an alien been incubating inside her chest, as an attempt to bring also grow this alien inside her and then remove it from her. This was the only way to get an alien specimen alive.

So, according to the movie plot, both species where with merged DNA, because the alien from the this movie franchise takes many characteristics of their live incubator specimen.

In the previous movie she killed herself in order to also kill the alien and not let the bad intentionalist company to keep the alien, in order to save Earth.

So in this case it was not from the same egg, but from the same DNA which was used to make many clones from her and the other alien species. In this movie they only made it all right in the 8th attempt. The other seven the DNA merged wrong and they were grown with bodies mixed.

Even the survivor Ripley number eight had some sort of mind connection with the aliens and also more strength and acid blood, just like the alien.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.