On one hand evolution seems to drive against the second law in that it creates a state of (locally) higher order.
On the other hand the second law seems to drives evolution - in the sense that it provides a constant fitness measure - essentially evolutionary fitness of life is a measure of its ability to maintain an ordered state in a system that naturally drives towards disorder. No entropy -> no evolution.
Wikipedia states: "and the second law follows because random chance alone practically guarantees that the system will evolve towards such thermodynamic equilibrium".
Which actually uses the word "evolve". But Evolution actually gives us a system that locally moves away from thermodynamic equilibrium giving us system of very high complexity (us!). What is the relationship between the 2nd law and evolution?

Applogies the question is vague. I understand that taken as a closed system the 2nd law holds - hence my careful use of "locally" - I never meant to suggest that evolution => 2nd law doesn't hold.
The essence of what bugs me I think is that it is odd that a law which essentially state that disorder increases seems to be dirrectly linked to (i.e be a driving force behind) evolution - which has given rise to some highly complex systems (albeit within a closed system that overall obeys the 2nd law). Without entropy and a natural tendance for things to decay there would be no selection. The 2nd law seems to provides a fitness function that is constantly applied in realtime to provide selection necessary to drive evolution.
It seems ironic that a law that implies an overall move to a state of disorder seems responsible for peaks of extreem complexity - indeed for some of the most complex systems known to science. So maybe my question becomes:
Does entropy and the 2nd law drive evolution? Its it true that a law that states that a closed system moves to a state of increasing disorder can also be responsable for extreem peaks of order within that system (that overall obeys the law)?

  • $\begingroup$ possible duplicate of Entropy and Crystal Growth $\endgroup$
    – jinawee
    Dec 22, 2013 at 11:06
  • $\begingroup$ @jinawee Michael Brown's answer is good, but I think the OP is also getting at something more general. Namely: can the concept of evolutionary fitness be meaningful independently of the concept of entropy? Ricibob can you please confirm? $\endgroup$ Dec 22, 2013 at 11:46
  • 2
    $\begingroup$ This is a common question among Christian fundamentalists, who generally do not understand science very well, and thus mistakenly believe that the 2nd law is in conflict with evolution. There are a wide variety of answers to this apparent "paradox" available in varying quality online, although user34039 and Boluc's answers below are good starting points. $\endgroup$ Dec 22, 2013 at 15:53
  • $\begingroup$ I wrote an article on the relationship between living systems and the 2nd law of thermodynamics, answers many of your contentions: hasansthoughts.blogspot.com.au/2013/07/… $\endgroup$
    – user34039
    Dec 23, 2013 at 0:13
  • $\begingroup$ +1 @DumpsterDoofus - apparently we're blocked from uprooting comments twice. $\endgroup$ Dec 23, 2013 at 2:08

3 Answers 3


The second law of thermodynamics only applies to closed systems. The earth is an open system (as it is continually receiving energy from the sun), hence the 2nd law doesn't apply to evolution and increase in complexity does not violate any laws.


The fault in this reasoning comes from the fact that you are inspecting a small part of the system (the biosphere) and ignoring the total entropy in the system. All biological processes, from those present in bacteria (or for multicellular organisms, mitochondria) to firing of neurons in human brains, increase the total entropy of system.


To my knowledge the relationship between the second law of thermodynamics and evolution is not as interesting as one might hope.

Firstly, evolution does not tell against the second law as noted in the other answers for the simple reason that life systems are driven by energy from the sun, or in the case of some deep sea life like the microbes and tube worms that thrive around undersea volcanic "smokers", they are driven by chemical energy and high-temperature heat from the volcanic material in a low-temperature icy abyssal environment. A good example of this is in Michael Brown's answer on crystal growth.

Indeed I would go further than this and say that one relationship between the second law of thermodynamics and evolution of life on Earth is that I think the latter, when you think of it as a grand experiment, or a grand simulation in the spirit of Douglas Adams's Earth-Designed-By-Deep-Thought, yields powerful support for the second law, maybe the strongest experimental evidence we have:

There are no biological perpetual motion machines of the second kind, and this is an extremely strong experimental null result

After 3 billion (and likely more like 4 billion) years of evolution, wherever biologists look, the basic powerhouses driving life (photosynthesis, mitochondrial ATP production from chemical energy ingested by cells and so forth) are well understood and almost certainly universal. It seems to me, that if there were a way around the second law through biological nanomachines (particularly with a variation on the Szilard engine, since the experiment cited in my footnote shows how it can scale to biological systems), evolution would almost certainly have found it by now and this second-law-violating process would be meeting all the needs of the creatures that evolved it. One could imagine that such creatures would swiftly become utterly dominant in the biosphere, sweeping all else aside. But this hasn't happened yet, although I believe there is an animal who delusionally believes that all its needs can be gotten for free from the environment, and that is just what that animal seems to be doing to the biosphere around it, so we have some anecdotal experiment evidence about how a second law violating animal might behave and how it might affect the biosphere. And yet, after all this time of life on Earth, all the creatures are using energy deriving processes altogether in keeping with the second law. Indeed the weird life (tube worms and the like) discovered in the last few decades around "volcanic smokers" deep in the ocean, almost poetically seem to be paying homage to Carnot's thought experiment, drawing work from heat and chemical potential blasting out of their central, hot life-giving "smoker" and casting the excess entropy out into the icy darkness surrounding their tiny thriving neighbourhood.

Part of your question seems to be can the concept of evolutionary fitness be meaningful independently of the concept of entropy? Or, could we have evolution in the if the second law didn't hold? Evolution and entropy are certainly related: you can't have evolution without minimisation of organism entropy (driven of course by the sun or volcanic smokers as noted above, such that the entropy of the total system still increases). To understand this, think of evolution as a search for fit creatures within a colossal "creature" configuration space: natural selection ends up confining the workable creatures to tiny neighbourhoods in this configuration space: if you imagine sampling a population of creatures, sequencing their DNA and working out an estimate for how many bits per creature defines that creature within the population, it will be a tiny fraction of the number of bits that can be encoded in each creatures genetic sequence. But I think this is independent of whether a decrease in creature entropy does or does not call for work as required by the second law of thermodynamics.

Footnote: An experiment wherein a working Maxwell Daemon was actually built and tested in the laboratory is described in:

Shoichi Toyabe; Takahiro Sagawa; Masahito Ueda; Eiro Muneyuki; Masaki Sano (2010-09-29). "Information heat engine: converting information to energy by feedback control". Nature Physics 6 (12): 988–992. arXiv:1009.5287. Bibcode:2011NatPh...6..988T. doi:10.1038/nphys1821. "We demonstrated that free energy is obtained by a feedback control using the information about the system; information is converted to free energy, as the first realization of Szilard-type Maxwell’s demon."


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