Are humans driving evolution in animals?

Feb 4, 2016

Photo credit: EPA


Are humans inadvertently driving evolution in other species? Mounting evidence suggests activities such as commercial fishing, angling and hunting, along with the use of pesticides and antibiotics, are leading to dramatic evolutionary changes.

Sitting down to a roast chicken dinner doesn’t seem like an obvious opportunity to consider evolution. But it is.

Think about it: those big tasty carrots, that plump, tender chicken and those handsome potatoes all differ markedly from their natural ancestors.

A wild carrot is barely more than a slightly enlarged purple tap-root and red jungle fowl certainly don’t have the extravagant cleavages found on modern broiler chickens.

The intentional selection of the qualities we like (such as flavour and size) in domesticated livestock and cultivated crops has led to descendent animals and plants that differ genetically from their ancestors. This change in gene frequency is evolution, and in this case has come about by a process called artificial selection.

Natural selection is basically the same process. The difference is that instead of humans selecting individuals to breed, natural selection pressures such as predation, or the reluctance of females to mate with lower quality males, cause some individuals in a population to prosper and produce offspring while others fare poorly, leaving fewer offspring.

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3 comments on “Are humans driving evolution in animals?

  • @OP picture. Bigger fish are preferentially removed from the sea, enabling genes for “smallness” to prosper

    Mesh sizes on nets, take out the bigger and more mature fish, so being small and breeding young is a selected survival strategy!

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  • I wrote an article about this a few years ago – and sent it to the European Fisheries commission and had a reply – basically telling me to shut up.

    The way that we fish is destined (designed is too strong a word) to create fish population collapses. If we selected as nature does – eat small juvenile fish and left the big ones. Then – barring pollution and CO2 issues – we could have a plentiful fish. Big mature cod produce millions of eggs – juvenile cod don’t. It’s as simple as that.

    I’ve also posted this on Richard Dawkins site before – and written to Hugh Fernleigh Whittingstall.
    Neither have replied.

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    We all believe that it is wrong to eat small juvenile fish rather than bigger more mature specimens. As the preferred choice of both fishermen and consumers, the policy of catching large fish and releasing small fish has been the tool for managing fish stocks since the 1880’s and there have been a lot of claims of the damage to fish stocks from catching juvenile fish.

    Increasing the mesh sizes of nets have been one the main methods used, where the catch is restricted to those animals that cannot escape through the gaps in the nets; selecting big fish whilst allowing small fish to escape. Under most national policies, fisherman have been legally obliged to throw back smaller fish they have accidently caught below a certain predetermined size.

    And not just fish, but most ocean harvest processes are geared to selectively catch large animals over small animals.

    I believe that this policy is one of the major factors contributing to the catastrophic collapses in fish stocks that have long been experienced by ocean fishermen, resulting in the massively depleted stocks seen throughout the world today.

    We should in fact, do the opposite; release the large animals and consume the small. Just as nature intended!


    For a population to remain stable in numbers and in weight, each individual in that population need produce one offspring who, in turn, reaches the same approximate age and weight and repeats the process.

    However, the majority of offspring of most organisms do not make it to this reproductive level, instead – ending up as part of the food chain. So many animals have evolved to produce massive numbers of eggs and larvae etc. to compensate for this loss.

    Fish in particular, have evolved to produce thousands – if not millions of offspring throughout their lifetimes. And the larger and more mature the fish are, the more physically able they are of producing ever greater numbers of eggs and offspring.

    Also, as these animals mature, they become more able to reproduce successfully by producing healthier eggs, have fewer predators and are more experienced in the arts of survival and reproduction.

    So though they are rarer in the population, they (statistically) will have a greater fecundity than their smaller, less mature counterparts who, though more numerous, produce less eggs, less healthy eggs, are less experienced at reproduction and more vulnerable to predation. Furthermore a greater proportion of them are not even sexually mature – so will be incapable of producing any offspring at all.

    In the natural world, it’s the largest, fittest, more mature and most able survivors who are the main producers of a population.

    And by removing large fish under present fishing policy, humans distort the natural order of this system and create a selective process to pressure fish populations away for being large and prolific – to being small and less prolific.

    The fittest are those that survive – and the fittest of our man made populations are small immature fish – so the system fails.

    This has been shown by research where fish are sexually maturing earlier and smaller – an indicator of selection against large size and consequently later maturation.


    An analogy would be like predominantly selecting breeding ewes rather the lambs for meat production. Lambs take more than a year to reach full optimal sexual maturity, so in the first year we would have a glut of mutton, second year little, and then the third year some but not much, and then even less the following year and so on – always getting less – with catastrophic collapses of meat supplies a regular occurrence – especially if the ewes are taken before lamb production. This is a typical pattern in fisheries.

    North Atlantic Cod are a particularly good example of such a catastrophic policy.

    A full grown North Atlantic Cod can reach up to 2 or more metres in length and these giants were common in the 19th century. A fish of this size will produce billions of eggs in its lifetime. It would almost be impossible to calculate the numbers of successful issue an individual full-grown Cod could contribute to the population.

    Cod of this size are now virtually extinct, they rarely grow beyond 1 metre. These smaller Cod that survive (those just under the minimum mesh size for Cod fisheries) are barely sexually mature, and will only be able to produce thousands of eggs before they are caught.


    So the conclusion must be that we do not harvest fish over a certain size but harvest juveniles under a certain size.

    The problems for the net fisheries industries to create a system to capture small shoaling pelagic and bottom feeding fish rather than large fish will be substantial and will require extensive research into fish habits and life cycles as well as a total redesign of net fish capture methods.

    Do fish shoals represent single ages groups for example; can we imitate natural capture methods such as whales use to select out smaller fish; sonic booms etc.

    Selection by line fishing it is a relatively simple process – hook sizes easily differentiate – small hooks do not catch large fish.

    As for the lobster, and crab fisheries it is also a simple change of habit. Lobster and crab catches are limited to the size of the hole they can crawl though into the lobster pot; big animals being unable to get in while small ones can.

    Proving this policy in the lab would be very simple, using tanked populations of breeding fish or other creatures (daphnia for instance) or in trout ponds

    If this policy were implemented, for single species, then we could see fish stocks stabilizing within 3 years and then start to rise – not withstanding pollution and climate change effects as well as destruction of habitat.

    Conor O’Sullivan

    BSc Marine Biology/Oceanography

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