From elements, chemical compounds, cells, multicellular organisms, society evolves and with each step possibilities increase and things get complex. We are builing structures like ribosome builds polypeptide chains.

So my question is why humans keeps continue to live, does our brain is unconsciously tries to get our society to get bigger, why life has a tendency to get complex with time?


I disagree with the assumption that biological systems have evolved to become more complex.

A clear example of the contrary is found in the Rickettsia species of bacteria which live inside the cells of its host (obligated intracellular parasites). Their genomes contain split genes, gene remnants and pseudogenes that may represent steps of a genome degradation process.

Here you can find more information about Rickettsia evolution.

Here you can find an essay about complexity as a driving force in evolution.


This is an old and interesting question: how do we explain apparent trends in evolution without falling into the trap of teleology or goal-directed evolution, the idea that evolution is working toward a particular end point?

I don't know the answer, and I don't know if anyone knows the answer, but at least two books have tackled the question in a serious way.

... [f]illing a previously empty niche does wonders for the reproductive success of an organism; variations which increase size make new niches available, and so are favorably selected. But, owing to constraints imposed by basic physics and chemistry, larger organisms must be more specialized internally, i.e. more complex, to be as efficient as smaller ones, or even just to survive, so the selection is especially favorable for larger and more complex organisms. Because of the way developmental processes work, this complexity will probably be retained even by later, smaller organisms in other niches. Voila: the evolution of complexity, by means of natural selection.

Bonner's argument might or might not work at the level of cultural evolution.

  • In contrast, McShea and Brandon argued in a 2010 book that random variation by itself should tend to increase complexity. McShea's summary:

even when forces and constraints are present, a tendency for complexity to increase is always present. The rationale is simply that when selection is absent, the parts of an organism should tend spontaneously to accumulate variation, and therefore to become more different from each other ... A consequence of the [Zero-Force Evolutionary Law ] is that we do not need natural selection to explain complex tissues and organ in organisms.

  • $\begingroup$ Part of the problem lies in measuring - or even defining - complexity in evolutionary terms. An example I read about (though I can't vouch for it) is the difference between amphibian and mammalian reproduction. Amphibians simply lay their eggs outside - which means their genes must be prepared to handle a wide range of environments and still produce an adult frog or salamander. Mammals keep their embryos inside, in a tightly-regulated environment. And then there's metamorphosis - are the different stages of a butterfly less complex than mammalian growth? $\endgroup$ – jamesqf Dec 27 '18 at 5:28
  • $\begingroup$ fair enough, but from a very broad perspective there are reasonable ways to define this that will distinguish bacteria from (say) kangaroos - number of cell types, variety of biochemical pathways, genome size, ... $\endgroup$ – Ben Bolker Dec 28 '18 at 17:43
  • $\begingroup$ @BenBolker Number of cell types is probably a good indicator / proxy for organisms, but it's hard to judge, because so far we have estimates for model organisms at best. Genome size is not correlated with organism complexity unless prokaryotes vs eukaryotes is all you care about. I would also be surprised if the number of actual biochemical (i.e. metabolic) pathways an organism has correlates with complexity, since higher eukaryotes are outsourcing a lot here; number of genetical pathways/circuits might again be viable though. $\endgroup$ – Nicolai Jan 14 at 18:03

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