My university professor stated that "individuals do not evolve, populations do". But aren't populations made up of individuals? That's like saying when a compound changes in stability, none of the elements' properties change. If someone could clear this up, that would be great.

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    $\begingroup$ If you pick pebbles of different colours, and then throw away all the light ones, is it the pebbles or your collection that have changed colour? $\endgroup$ – Joce Nov 18 '16 at 10:47
  • $\begingroup$ Populations are made up of individuals, but you have to remember that the individuals in the population now ("after the evolution happened") are different from the individuals in the population then ("before the evolution happened"). $\endgroup$ – R.M. Nov 18 '16 at 20:06
  • $\begingroup$ Or in simple terms evolution is an emergent characteristic, A single individual can no more evolve than a single number by itself can undergo addition or a single car can be called gridlock traffic. $\endgroup$ – John Mar 12 '17 at 6:22

The statement individuals do not evolve, populations do is rooted in the (classical population genetic) definition of evolution. Here is this definition:

Evolution is a change of allele frequency through time in a population

Evolution is defined for a population, it is not defined for an individual. And it makes intuitive sense once you get more used to how evolution works. For example, the so-called fundamental principle of natural selection states that at any given time, the rate of increase in the population mean fitness is exactly equal to the variance in fitness.

Indeed, evolution is all about phenotypic and genetic variance (for fitness or other phenotypic traits) and without a population to observe, there is no variance. It is within this framework that people say individuals do not evolve, populations do but you are correct that as populations evolve its constituents (the individuals) changes. The sentence has the advantage to reinforce the concept that evolution happens at the level of the population.

  • $\begingroup$ As an ecologist I would say that evolution is a bit more than the genetic definition of changes in allele frequency. It is the natural selection that occurs on these differences, were less adapted individuals produce less offspring on average. And in that sense, evolution does happen to individuals: they die or fail to reproduce. But the effect of the adaption occurs in the next generations, at the population level. $\endgroup$ – RHA Mar 9 '17 at 12:47
  • $\begingroup$ The sentence individuals do not evolve, populations do is more of a catchy phrase that force an intuition that a fact. By definition, NS is a fitness differential in the population. While the fitness are properties of individuals, fitness variation among individuals is a property of a population. Similar notion apply to any other evolutionary forces. If you do a tiny bit of modelling in evolutionary biology, you'll realize that you will always use population-level variables (variables that vary among individuals). It is with this in mind that the quote makes sense. $\endgroup$ – Remi.b Mar 9 '17 at 15:08

Evolution itself is a term that describes populations changing over time.

As Remi.b pointed out, if you take evolution to be genetic changes in a population over time, then it doesn't make sense for an individual to evolve. Evolution can only occur as genetic changes are inherited from parents to their offspring.

A given individual in a population can be subject to natural selection, but the individual itself cannot 'evolve' in the biological sense of the word. They can only contribute to the evolution of a population by affecting the allele frequencies in that population.

As an analogy,

The evolution of a population can be thought of as a motion picture of that population.

At any given moment, the genetic structure of a population can be thought of as a screenshot, and one person (or organism) can be thought of as a pixel.

Evolution is like watching a video of a population change through time.

So you might say:

"pixels do not play, videos do".

  • $\begingroup$ Actually, this does answer the question. If you think it's a bad answer, you can downvote it. $\endgroup$ – canadianer Mar 3 '17 at 16:22

Evolution is about children differing from their parents. You are not identical to your parents.

  • Your cells' DNA does change (a little, through new random mutations from time to time, most of it being repaired but not always correctly), but incoherently through cells, and these mutations are not transmissible if they are not happening in your gametes (sex cells).
  • Non-lethal changes in your gametes are transmitted. Besides, errors in chromosome duplication is a way more efficient and fast way of evolving (mixing sentences makes sense more easily than mixing letters).
  • $\begingroup$ Downvoters, please justify. $\endgroup$ – Fabrice NEYRET Mar 8 '17 at 8:47
  • $\begingroup$ I don't really see how your answer specifically answers the question. You talk a little bit about the mechanical origin of mutations but it does not quite relate to the core of the question. (I was not the one down voting btw but I kinda agree with the down vote). $\endgroup$ – Remi.b Mar 12 '17 at 6:10
  • $\begingroup$ because all the point is about : - many cells inheriting mutation of one single parent cell vs many cells mutating incoherently - mutation transmitted vs not transmitted - change by raw mutations vs change by replication error $\endgroup$ – Fabrice NEYRET Mar 12 '17 at 11:16

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