In this video Richard Dawkins talk about intermediate fossils. He describes how the whales were evolved from a common ancestor who lived on land.

But his theory sounds more like a devolution. I thought evolution was coming from the sea to the land and then to the skies. Are there more examples where species evolve back and forth between the ocean and land or skies?

enter image description here

  • $\begingroup$ If you change your thought of evolution to mean "getting better" to simply "changing", it becomes clear that loss of function in exchange for another is really no different than gaining function from nothing. $\endgroup$
    – user3970
    Commented Feb 8, 2019 at 1:52

3 Answers 3


Does evolution go only in one direction?

No, it does not. There is no such thing as a goal of evolution at making things fly or at making things intelligent or whatever. There is no intrinsic directionality.

In short the reasons are 1) Evolution is much more than just natural selection 2) natural selection does not systematically select for a specific trait. Some traits are advantageous under some ocnditions, some other traits are advantageous under other conditions.

I won't talk more about the mechanisms of evolution here as it would take a whole book. Instead I will recommend a source of information for you to further your knowledge.

Source of information

As your question is very introductory and shows misunderstanding, you might want to have a look at an intro course to evolutionary biology such as for example Evo101 by UC Berkeley.


Note that this term is rarely used in the scientific literature (actually I think I have never encountered it in the scientific literature). From wikipedia:

In modern biology the term [devolution] is meaningless: evolutionary science deals with selection or adaptation that results in populations of organisms genetically different from their ancestral forms, where evolution has no intrinsic directionality. The discipline makes no general distinction between changes leading to populations of forms less complex or more complex than their ancestors, and in such terms the concept of a primitive species cannot be defined.

The question is a bit unclear

There is a slight issue with the question as it is not that easy to categorize all animals as living strictly in the water, on land or in the sky. Note that almost no living things live strictly in the sky without ever touching the ground. Here are a few examples of limit cases

  • oysters
  • dragonflies (larvea live in the water, adult fly)
  • flying squirrels
  • Most ducks (spend much time on water but nest on land)

As a consequence the question is very undefined

Examples of potential interest to you

The question is undefined but here are a few examples of cases anyway that will interest you. For simplicity, I will reduce my list to animals only and will not consider similar cases in procaryotes, and non-animal eukaryotes such as plants and fungi.

Whose ancestors were terrestrial

  • Cetacea (blue whale, orca, dolphins, ...)
  • Sirenia (dugong and manatees)
  • Pinnipeds (sea lions, sea leopards, ...)
  • Monotremes
  • Marine iguana (and other swimming lizards)
  • Beavers
  • Otters

Whose ancestors were flying

  • Penguins
  • ratites (Ostrich, emu, kiwi, ...)
  • dodo
  • Many birds are able to stay for relatively long period under water when hunting for fish.
  • Ants and other non-flying hymenopterans.
  • Ground beetles and other non-flying beetles
  • water beetle

Again, categorization is not that easy. I just want to highlight the water beetle as example where the ancestor was marine, then terrestrial, then flying, then non-flying and finally living in the water again.

Related post

How many times did terrestrial life emerge from the ocean?

  • $\begingroup$ It is still hard for me to believe if I start swimming in the water and all my offspring also they will eventually start growing fins. Down the road, someone will develop something like it. How will that get introduced into their DNA? Shouldn't we be able to see in DNA if changes like evolution are possible in DNA? Mutations do not follow the outside pressures or need but they are just errors in the system. $\endgroup$
    – Grasper
    Commented Sep 11, 2017 at 15:17
  • $\begingroup$ @Grasper: DNA isn't really as straightforward as you seem to think. There's not a simple mutation for "fins" vs "feet", but different genes being expressed differently. Consider phocomelia, a condition where factors like pre-natal exposure to a drug produces flipper-like arms & legs: en.wikipedia.org/wiki/Phocomelia Then any mutations are selected for or against from a population of millions over thousands of generations. $\endgroup$
    – jamesqf
    Commented Sep 11, 2017 at 17:36
  • $\begingroup$ @Grasper You are right to have a hard time to think that your direct offspring will all of sudden and out of the blue grow fins if you swim a lot. But this is not what the evolutionary theory is claiming. I won't give you a whole intro course to evolutionary biology because it takes a lot of time and many other people have already done so. $\endgroup$
    – Remi.b
    Commented Sep 11, 2017 at 18:28
  • $\begingroup$ @Grasper Please just have a look at an intro course to evolutionary biology and you'll understand a little bit of what evolution is about. As recommended above, you might want to have a look at Evo101, a very short and very introductory course to evolution. $\endgroup$
    – Remi.b
    Commented Sep 11, 2017 at 18:28

Evolution helps an organism to be successful in the environment in which it lives. In this case, the organism evolved to suit it's aquatic environment. So there's nothing called devolution. For example, the cave proteus is blind while it's ancestors weren't. It does not mean that it has devolved. It doesn't require well developed eyes in a dark cave. So it has evolved to suit it's environment. Same case here.

  • $\begingroup$ Isn't that called adaptation? $\endgroup$
    – Grasper
    Commented Sep 11, 2017 at 14:58
  • 1
    $\begingroup$ Welcome to Biology.SE! Please add some more details and references in your answer. $\endgroup$ Commented Sep 11, 2017 at 15:28

Adaption gradually leads to permanent changes...which is evolution. The most favourable,adapted character passes on to the next generation and it leads to evolution. Adaptation and evolution are mutually inclusive events.

  • $\begingroup$ You do not seem to fully understand the definitions of evolution and adaptation. In the future, you might want to answer question in the fields in which you have at least some intro knowledge $\endgroup$
    – Remi.b
    Commented Sep 11, 2017 at 18:30
  • $\begingroup$ Is there any reasons for posting two independent answers rather than just expanding on a previous answer? Note that you can use the "edit" button to edit an existing answer. $\endgroup$
    – Remi.b
    Commented Sep 11, 2017 at 18:31
  • $\begingroup$ Oh. Can you help me with that if possible? I'll be really happy to gain some knowledge $\endgroup$
    – Akil
    Commented Sep 11, 2017 at 18:32
  • $\begingroup$ @Remi.b I'm new to stack exchange! Thanks man! $\endgroup$
    – Akil
    Commented Sep 11, 2017 at 18:33
  • $\begingroup$ No worries. I'll be happy to take some time to answer a post you may want to open. Asking a clearly defined question can be challenging (and it is not uncommon for new users to see their post getting closed), so it may be good to start with an intro course and build from there. As recommended to Grasper, you may want to have a look at Evo 101. Welcome to Biology.SE (and other SE websites) and Good luck! $\endgroup$
    – Remi.b
    Commented Sep 11, 2017 at 18:35

You must log in to answer this question.

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