I have heard that "The animals who have their 'EARS' outside their body give birth to their young ones and the animals who have their 'EARS' inside their body lay eggs." Is this true? Are there counterexamples?


3 Answers 3


You are quoting from Imam Ali,

"The animals who have their 'EARS' outside their body give birth to their young ones and the animals who have their 'EARS' inside their body lay eggs."

And in short the answer is that is wrong. Giving birth to live young is called vivipary. When a species lays eggs it is called oviparity. There are other mechanisms too.

Ovuliparity: fecundation is external (in arthropods and fishes, most of frogs)

Oviparity: fecundation is internal, the female lays zygotes as eggs with important vitellus (typically birds)

Ovo-viviparity: or oviparity with retention of zygotes in the female’s body or in the male’s body, but there are no trophic interactions between zygote and parents. (Anguis fragilis is an example of ovo-viviparity.) In the sea horse, zygotes are retained in the male’s ventral "marsupium". In the frog Rhinoderma darwinii, the zygotes developed in the vocal sac. In the frog Rheobatrachus, zygotes developed in the stomach.

Histotrophic viviparity: the zygotes developed in the female’s oviducts, but find their nutriments by oophagy or adelphophagy (intra-uterine cannibalism in some sharks or in the black salamander Salamandra atra).

Hemotrophic viviparity: nutriments are provided by the female, often through placenta. In the frog Gastrotheca ovifera, embryos are fed by the mother through specialized gills. The lizard Pseudomoia pagenstecheri and most mammals exhibit a hemotrophic viviparity.

Though it is true that most typically we would associate egg laying with animals with ears "inside" such as birds and snakes, there are some examples that are not this way. Boa constrictors are one species which gives birth to live young rather than laying an egg and being a snake their ears are 'inside their body'. However I should point out that this is Ovoviviparity, not viviparity. For an example of a lizard with viviparity see the Pseudomoia lizard genus.

  • $\begingroup$ Good answer +1. Although there are some counterexamples, there is still quite a high correlation between having ears inside/outside and being oviparous or viviparous. So why is there a correlation? It is certainly only due to phylogenetic correlation. If one make a study and decorrelate the effect of phylogeny, he would, I guess, find out that there is no significant correlation between ears position and viviparity/oviparity. $\endgroup$
    – Remi.b
    Jul 30, 2013 at 14:26
  • $\begingroup$ @Remi.b I agree, it is likely just a correlational relationship, rather than causal, but perhaps environments/lifestyles where external ears are less useful (e.g. underwater for reduced drag) are also typically less favourable to the birth of live young. I can imagine a bird doesn't want ears because they cause drag and wants to lay eggs to reduce the time it spends carrying the weight of a chick(s) - I'd imagine a pregnant bird would suffer from the extra weight when trying to fly. $\endgroup$
    – rg255
    Jul 30, 2013 at 14:35
  • $\begingroup$ @GriffinEvo Kindly excuse me for though people liked your answer more than that of anyone else but may be because of my lack of knowledge, I found terdon answer rather good and easy to understand be to accepted. $\endgroup$
    – kashif
    Jul 31, 2013 at 23:23

Just to expand on @rg255's very good answer, you could make the same sort of claim using just about any characteristic that is more commonly found in mammals.

Giving birth to live young is a characteristic of most (see the platypus below), if not all, mammals. Therefore, you could make the statement about external ears (also more common to mammals) using any other mammal specific body plan. For example:

"The animals who have their 'TESTICLES' outside their body give birth to their young ones and the animals who have their 'TESTICLES' inside their body lay eggs."

I am pretty sure you will find that this is as true as the statement about ears.

As in all other debates about this kind of thing, the platypus comes along and complicates things. This beastie has no external ears (or external testicles for that matter), it has tiny ear slits instead and it lays eggs. So, even this extreme weirdo seems to follow the ears (or testicles) on the inside means eggs rule. However, it is a mammal, it produces milk that it will feed to its newly hatched young like all mammals (well, almost, it doesn't have teats and instead the young suck up their mother's milk through her spongy belly).

A more straightforward and well known example that directly contradicts the ears claim is the dolphin. Dolphin ears are small holes on the sides of their heads but they give birth to live young as do all sea mammals. In fact, I am pretty sure that all sea mammals lack external ears (and cetaceans at least also lack external testicles) but give birth to live young. So seals, sea lions, walruses etc also contradict the ears rule.

In conclusion, no it is not true that all animals with internal ears lay eggs.

  • $\begingroup$ Actually there is a lot of variation in testes among mammals (descended vs. undescended, scrotal vs. astrotal): biology.stackexchange.com/questions/559/… $\endgroup$
    – kmm
    Aug 2, 2013 at 16:14
  • $\begingroup$ @kmm ah, but can you name an animal with external testes that lays eggs :) ? Anyway, that was just a tongue in cheek example to highlight the arbitrary nature of the distinction mentioned by the OP. $\endgroup$
    – terdon
    Aug 2, 2013 at 16:17
  • $\begingroup$ on a similar tongue in cheek note... I can't think of any animals with testes that lay eggs or have a pregnancy ;) $\endgroup$
    – rg255
    Aug 14, 2013 at 12:12
  • 1
    $\begingroup$ @GriffinEvo stretching the definition of having testes, the male angler fish will attach itself to the female and wither away leaving, essentially, only its gonads attached which the female will use to fertilize her eggs. Strictly speaking, at that point she has both testes of a sort and lays eggs :). $\endgroup$
    – terdon
    Aug 20, 2013 at 9:38

Internal or external ears is Not Relavent to an animal giving birth or laying eggs... Examples Sea Lions - External Ears - Live Birth Seal - Internal Ears - Live Birth

Sharks - Internal Ear - Eggs (Oviparous), Live Birth (Viviparious), and Egg cases in mothers womb hatch producing young that feed on siblings before a live birth (Ovoviviparious)

Dolphins - Internal Ears - Live Birth

Frogs - Have an external ear drum - Lay Eggs Exhidna (mammal) - Internal Ears - Lay Eggs

There is no relation to animal ears being internal(inside)/external(outside) to laying eggs or giving live birth.

I am a Biologist having worked at with a large variety of animals (egg layers and live birth) for 14 years. Feel free to ask any questions you may have. And by all means please do your own research to see the information I've provided is accurate. Great Inquary, I hear of lots of fun facts to remember things...some true, some not True Fact... You can SEE a SEA Lions ears but A SEALS ears are SEALED up


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .