I am confused, can evolution ( speciation ) really occur in such a short time ?

In 1971, biologists moved five adult pairs of Italian wall lizards from their home island of Pod Kopiste, in the South Adriatic Sea, to the neighboring island of Pod Mrcaru. Now, an international team of researchers has shown that introducing these small, green-backed lizards, Podarcis sicula, to a new environment caused them to undergo rapid and large-scale evolutionary changes."

Here is a short video featuring the scientist.

Two related articles:

Edit: I asked a similar question previously about two people having 44 chromosomes and their possibility of creating a new species. You might like to read/answer that as well:

Can two humans with 44 chromosomes produce viable offspring?

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    $\begingroup$ Evolution just depends on the amount of selective pressure. The classic selection for antibiotic resistance is just a single generation. It may seem artificial, but it is adaptation in a single generation. Also wanted to add this link: yeast become multicellular in a 60 generations. scientificamerican.com/article.cfm?id=test-tube-yeast-evolve $\endgroup$
    – shigeta
    Commented Dec 18, 2012 at 20:59

2 Answers 2


I am confused, can evolution ( speciation ) really occur in such a short time?

Well, Evolution and Speciation are not the same. Evolution is the adaptation of an existing species to an environment over generations. Speciation is the development of a new species, and the definition of "species" can vary depending on who you talk to - but a very commonly accepted one is that two individuals cannot produce fertile offspring.

However, the answer is still Yes. Evolution can occur in as little as two generations because that's all the time it takes for a change in the DNA to be exhibited in the newest generation. For instance, Lactase Persistence - which allows the bearers to ingest dairy products without digestive stress into adulthood - has evolved at least twice in humans in separate groups. Both are the result of either one or two point mutations (single changes in a Nucleotide within the DNA). The result is that at one point in time for each appearance of lactase persistence, a child was born that could drink milk into adulthood while their parents and cousins could not.

That is evolution; the child was better adapted to the resources available, and because lactase persistence either...

  • Provided a significant advantage over their kin in the environment (which is likely, as being able to digest milk in an agrarian society opens up a new source of energy)...


  • Didn't hinder the child's ability to grow and produce fertile offspring of their own...

...it has persisted in the populations where it initially evolved.

Speciation is a little trickier, but that's because there isn't a known qualitative way to differentiate species at the genetic level quite yet. It could be a few key gene changes, it could be a whole genome difference of 10%, or a million other factors. Practically speaking, though, Speciation is simply the result of accumulated genome changes that at some point prevent the members of one group from producing fertile offspring with their ancestral group.

Because we simply don't know how much of or where the genome has to change, it's certainly possible that speciation could occur in the same time period as it takes to evolve: Two generations.

Since I'm doubting the wall lizards have a generational time of >37 years (don't mistake it for lifespan, humans can reproduce in our teens - even if we live into our 80's), it's definitely possible that the wall lizards could evolve (and potentially speciate) in such a short amount of time.

With organisms that have a very, very short generational time - like E. coli or other bacteria - you can observe the Evolution of populations in days or hours.

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    $\begingroup$ Clarified with your correction. $\endgroup$
    – MCM
    Commented Dec 19, 2012 at 0:04
  • $\begingroup$ I want to underline 1 fact about speciation, although you don't object to this. Speciation doesn't necessarily mean the lack of ability to produce healthy offsprings. For instance, Lions and Tigers ( Two different species) can reproduce healthy offsprings (Liger and Tiglons), but they don't mate in the nature. So speciation also requires the lack of inclination to mating with the other. $\endgroup$
    – Özgür
    Commented Dec 23, 2012 at 21:54
  • $\begingroup$ @MCM I have updated the question. You might like to answer the referenced question as well, please do :) $\endgroup$
    – Özgür
    Commented Dec 23, 2012 at 21:59
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    $\begingroup$ @Comptrol: the problem lies in the hazy definition of species. Often you would hear that two different species cannot produce fertile offspring, for instance. $\endgroup$
    – nico
    Commented Jan 4, 2013 at 17:18
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    $\begingroup$ @MCM - would you be against editing "Evolution is the adaptation of an existing species to an environment over generations." to "Evolution is a change in the characteristics of a population over generations." The existing sentence describes the response to selection, but evolution occurs by drift, mutation, and migration $\endgroup$
    – rg255
    Commented Jan 10, 2016 at 12:18

Evolution can occur in just one full generation

Strong selection will rapidly reduce the gene frequencies of genes which cause negatively selected phenotypes. This reduces the likelihood of unfavourable genotypes occurring in the next generation.

(I regard generation here as the complete cycle of one individual being born to the point at which they successfully give birth/sire young).

Population genetics explanation:

Imagine a population in which LOC1 is a locus affecting a phenotypic marker allowing perfect identification of genotype at that locus. There are two alleles at LOC1, A and a. This gives rise to three different genotypes, AA, Aa and aa which occur in the population in equal proportions. Those individuals with AA exhibit a certain trait, whilst Aa and aa individuals do not. If only the AA genotypes are allowed to mate then the following generation will only contain AA genotypes at LOC1 (assuming no mutation).

For more population genetics read Principles of Population Genetics and then Introduction to Quantitative Genetics.

Genetic drift caused by using 5 Pairs

The new population was started with just 5 pairs of individuals. This means there is huge potential for fixation of alleles via drift with in the very first generation. I ran a (basic) genetic drift simulation in R just now. Out of 5000 replicates 4709 went to fixation (Single locus, two alleles, using 30 generations of 10 individuals).

Environmental change can cause hidden genetic variation to be exhibited

Molecular regulators which affect the expression of traits can respond differently depending on environmental influences. This point is summarized nicely by the opening lines of this paper- thanks to @leonardo for this point.

Hsp90 is a molecular chaperone for many signal transducers and may influence evolution by releasing previously silent genetic variation in response to environmental change. In fungi separated by 800 million years of evolution, Hsp90 potentiated the evolution of drug resistance in a different way, by enabling new mutations to have immediate phenotypic consequences.

Evolution and speciation are different things

These are just the simple wikipedia definitions, for better ones then consult the literature:

Evolution is the change in the inherited characteristics of biological populations over successive generations.

For a good thorough introductory text on evolution I recommend Evolution by Mark Ridley (not to be confused with Matt Ridley - popular evolution science writer).

Speciation is the evolutionary process by which new biological species arise.

Speciation, thanks to a long fought debate over species concepts, is also an ambiguous process. What some species concepts would define as two distinct species, another would call one species, and another may call them 10 species! Seemingly everyone who specializes in the study of speciation would have there own twist on a species concept so don't expect that argument to resolve any time soon! It's not advanced much since Dobzhansky wrote this.

The species concept is one of the oldest and most fundamental in biology. And yet it is almost universally conceded that no satisfactory definition of what constitutes a species has ever been proposed.

When does evolution occur? and when is change not evolution in such a short time?

I've put this bit in because what I find is a strange, but common, question people ask is

"species X has changed/adapted to novel selection very rapidly, has evolution really occurred?"

The way people ask this makes it sound like they want a certain amount of evolution to occur before we can say something has evolved. To me saying evolution has occurred means that some change has occurred, via any of the mechanisms of evolution, which results in one subset of individuals being different from another it is compared to (spatially or temporally separated). You could ask if such strong evolution can really occur over a short time period, but the answer is obvious - yes it can. If it has occurred then why do you think it is exceptional? what is your alternative explanation for the differences seen?

  • $\begingroup$ You can also look to the work on heat-shock protein 90 (Hsp90) and specifically the scientist Susan Lindquist for human evolution within one's lifetime. $\endgroup$
    – user560
    Commented Dec 25, 2012 at 0:47
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    $\begingroup$ also; the fact they only introduced five pairs means there could have been a lot of change in the first generation via genetic drift - I'll edit that, and some examples of rapid evolution, in to the answer soon - thanks @leonardo $\endgroup$
    – rg255
    Commented Dec 25, 2012 at 9:33

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