Mammals Can “Choose” the Sex of their Offspring

0

Mammals can skew the male-female ratio of their offspring in order to maximize their reproductive success, new research finds.


The study, published today (July 10) in the journal PLOS ONE, confirms a long-held theory that animals can influence the sex of their young in response to environmental conditions and other factors. The results come from about 90 years' worth of records for 40,000 mammals, ranging from primates to rhinoceroses, at the San Diego Zoo.

Females that produced the most males went on to have up to 2.7 times the number of grandchildren from those sons as those who had even numbers of male and female offspring.

"When mothers produced predominantly male offspring, those male offspring outcompeted their peers," said study co-author Joseph Garner, an ethologist at Stanford University.

Parents that produced more females also tended to produce more offspring from those daughters than those with an even gender split, though the effect was less pronounced.

 

Written By: Tia Ghose
continue to source article at livescience.com

NO COMMENTS

  1. I have been trying to figure out why this would work. Here is a hypothesis for Humans.

    I remember from my high school days, students who had an elder brother were very popular with girls. The older brother was very appealing to them. Brothers are girl bait for each other. However that should work just as well in a family with an older brother and two younger sisters.

    • In reply to #1 by Roedy:

      I have been trying to figure out why this would work. Here is a hypothesis for Humans.

      I remember from my high school days, students who had an elder brother were very popular with girls. The older brother was very appealing to them. Brothers are girl bait for each other. However that should work…

      That might be a factor for humans but there is a much simpler reason for gender preferences in all mammals. The effort (time, food, etc) required for a male to reproduce is trivial compared to a female. Not just an order of magnitude but several orders of magnitude. For a human female for example they can reproduce at most once every nine months. A male can impregnate thousands of women in that same time period. From the standpoint of reproductive success it is a far more successful strategy to have male children rather than females. I’ve been reading some anthropology/biology stuff lately and that is almost certainly one of the drivers for why so many primitive cultures practiced (and some still do) female infanticide and also probably why patriarchal cultures tended to dominate.

  2. Having read the article, I can’t see that there is any indication that there isany kind of manipulation or environment influence taking place. It simply states those who have children of predominantly one sex have more grand children. That doesn’t imply there’s any kind of force influencing mothers to have predominantly one sex other than their own genetics.

    There may be some kind of selection, genetic selection working on an evolutionary scale, or there may be a social selection as Roedy mentioned favouring siblings of the same sex, but their is certainly no ‘choosing’ going on, concious or not. The mother has no influence as to what sex her children are, just that IF she has predominantly one sex they’ll fare better.

    This headline is completely and utterly misleading.

    • This headline is completely and utterly misleading.>>

      I am feeling the same way. At least they put choose in quotes, though. Maybe they just couldn’t think of a better word (that would sell the article)…..

      In reply to #2 by Seraphor:

      Having read the article, I can’t see that there is any indication that there isany kind of manipulation or environment influence taking place. It simply states those who have children of predominantly one sex have more grand children. That doesn’t imply there’s any kind of force influencing mothers…

      • In reply to #3 by crookedshoes:

        This headline is completely and utterly misleading.>>

        I am feeling the same way. At least they put choose in quotes, though. Maybe they just couldn’t think of a better word (that would sell the article)…..

        In reply to #2 by Seraphor:

        Having read the article, I can’t see that there is any indi…

        I suppose they were trying for ultimately, or at the level of the genes, but could not get that into a title comfortably, or perhaps understandably.

        • I suppose… and the truth is, the real title (or what it should be) wouldn’t attract the average reader (or the least common denominator).

          In reply to #7 by Neodarwinian:

          In reply to #3 by crookedshoes:

          This headline is completely and utterly misleading.>>

          I am feeling the same way. At least they put choose in quotes, though. Maybe they just couldn’t think of a better word (that would sell the article)…..

          In reply to #2 by Seraphor:

          Having read the article, I…

          • In reply to #8 by crookedshoes:

            I suppose… and the truth is, the real title (or what it should be) wouldn’t attract the average reader (or the least common denominator).

            In reply to #7 by Neodarwinian:

            In reply to #3 by crookedshoes:

            This headline is completely and utterly misleading.>>

            I am feeling the same way. At least t…

            Went over the article closely and it seems to me to be rather ” old hat ” to say the least. Nothing new here. Did you see something?

          • Nah, same shit over and over.

            In reply to #9 by Neodarwinian:

            In reply to #8 by crookedshoes:

            I suppose… and the truth is, the real title (or what it should be) wouldn’t attract the average reader (or the least common denominator).

            In reply to #7 by Neodarwinian:

            In reply to #3 by crookedshoes:

            This headline is completely and utterly misleading.>>

            I am…

          • In reply to #8 by crookedshoes:

            Hi crookedshoes,

            I suppose… and the truth is, the real title (or what it should be) wouldn’t attract the average reader (or the least common denominator).

            It seems to me that bad science reporting, like this example, are often not the fault of the journalist – but of the editor.

            The journalist has included all the pertinent facts which show that the headline is totally misleading in the main story (which, my best guess, were mostly shuffled to the bottom of the story by the Editor too).

            In Comment 2 you correctly guessed:

            Maybe they just couldn’t think of a better word (that would sell the article)

            The key word is sell.

            I’ve worked in sales and marketing (forgive me Bill) and I can see the commercial imperative – perhaps – more clearly than most. Be that as it may, there is no escaping that fact that publications – even wholly on-line ones – are in the cyclic business of building audience, to attract advertisers, to fund reporting, to build (etc.).

            If the headline had been: Environmental Factors Skew Gender Ratios, or Meticulous Record Search Confirms Birth Rate Theory how many fewer clicks would Live Science have got?

            After decades of media watching (by which I mean study – rather than living my life as a Couch Potato), it is clear that this is a common theme. The commercial imperative has many good points – and it is ideal for many forms of human endeavour – but it has a poisoning effect on factual reporting.

            Commercially run media is bad for us. We get less facts, badly reported and with added editorial distortion (again: Live Science provides evidence – example: For instance, high-status males typically have more children, so wealthy parents may benefit from having mostly males … Anecdotally, former presidential nominee and billionaire Mitt Romney has five sons.).

            It is often argued that, on the up-side, we do get media that people consume (audiences are built).

            But this exposes another problem with commercially run media; wouldn’t we prefer, as democratic citizens, to have media that engages?

            This is why traditional media hate the Net. The Net is interactive by default, engages critical thinking and adds fact-checking.

            Live Science is a low-quality science site, and the linked story demonstrates this in spades. It is Old School media, and as such should be avoided by anyone seeking truth.

            Peace.

    • In reply to #2 by Seraphor:

      Having read the article, I can’t see that there is any indication that there isany kind of manipulation or environment influence taking place. It simply states those who have children of predominantly one sex have more grand children. That doesn’t imply there’s any kind of force influencing mothers…

      I’m just an amateur in biology but my interpretation of the article is that you are correct but you aren’t getting what the researchers were trying to demonstrate. (And of course it gets muddied as always by bad science reporting that goes for the sensational headline) The hypothesis they are testing has two components: 1) Mammals can control (influence might be a better word) the gender of their offspring and 2) Influencing the gender of offspring based on environmental factors (i.e. sometimes it can be better to have more sons some time more daughters) will increase reproductive success

      So this study was just testing sub-hypothesis two. It was showing that for mammals who based on the data influenced the gender of their off spring (the genders didn’t correspond to what we would expect from a purely random distribution) for those mammals they had better reproductive success then those that didn’t. So the second part of the hypothesis is supported. Exactly how they influence the gender is a totally different question..

      Anyway, that was my reading of it, if someone has an alternative view would like to hear it.

  3. There is no direct benefit in producing more male offspring. As Dawkins explains in one of his books: Even though males can produce far more offspring than females, they don’t – for the simple reason that every sibling has exactly one father and one mother. So, on average, males and females produce exactly the same number of siblings.

    If one sex is over-represented, (say, there’s twice as many males as females) then the average number of offspring drops for the males – to half the average of the females. If you could “choose” the sex of your offspring, then logic dictates that you should choose the under-represented sex, if there is such a sex. Usually there isn’t.

    The article might be on to something – but not something simple or obvious. I hope Prof. Dawkins had something to add to this topic.

    • In reply to #6 by Nibla:

      There is no direct benefit in producing more male offspring. As Dawkins explains in one of his books: Even though males can produce far more offspring than females, they don’t – for the simple reason that every sibling has exactly one father and one mother. So, on average, males and females produce exactly the same number of siblings

      Do you remember which Dawkins book that was in? That is a good response but I’m not completely convinced. The thing is in many situations average number of children is irrelevant. For example, if I am the chief of a primitive tribe I have access to many females. Its likely that my male offspring will more likely be chiefs as well since they have the advantage of being my sons and my chiefy genes. So for a chief to have lots of sons is a better strategy for ultimate reproductive success then to have daughters. BTW, there is sort of a converse as well, for low status individuals daughters may be more productive. The female (since she has to do most of the work) is the focus of male competition. So low status males are more likely to not procreate at all, where as low status females still probably will procreate, there is always a demand for more fertile wombs so to speak. This may be born out in some anthropological research, wealthy individuals tend to have more sons and poorer ones more daughters — although to my konwledge its not something everyone agrees on yet I think there is some evidence for it.

      • In reply to #11 by Red Dog:
        [On the benefits of male/female children depending on social status]
        That sounds plausable to me. I can see how that would work.

        On another track: I’ve once visited a large ape-reservoir, “de Apenheul”, in the Netherlands. I was told (by an excellent guide) that, in the tribe of squirrel monkeys, there were tens of females and only 3 males. “How come?” I asked.
        Well: In nature, a tribe of females would allow just a few males between them. All others would be driven away. Since the zoo didn’t have room to have monkeys driven away, they were transported away, to another zoo, that held a tribe of only males.
        Such trading must happen a lot in zoos. It can not have been easy to extract any meaningful data from such brutal selection.

          • In reply to #18 by chris 116:

            In reply to #17 by Red Dog:

            And another thing: look at the Trivers-Willard hypothesis.

            Thanks again. Are there any books by or about Trivers (besides The Folly of Fools) that you would recommend that are similar to Dawkins’ books? I mean things written for an audience that is literate about science in general but not experts in biology? I keep seeing Trivers name come up in other things I’m reading (about behavioral/psych/social issues and biology) but except for The Folly of Fools what I recall finding by Trivers were just papers that seemed very interesting but beyond my current level of knowledge.

    • In reply to #6 by Nibla:

      The article might be on to something – but not something simple or obvious. I hope Prof. Dawkins had something to add to this topic.

      I agree. I wish he wouldn’t spend so much time on tweets and would spend a bit more time engaging in dialogues on issues like this.

  4. Well, the title got me to look at the article – so, I suppose it succeeded. But, as noted by everyone, there wasn’t any choice involved. And there wasn’t any information pertinent to natural selection or evolution or any such thing – it was all observations of zoo animals. They did observe that there appeared to be sperm from different species that produced more or fewer male offspring than average. I know a couple of humans that have that characteristic, too. The father of 6 girls, for example. I’ll have to see if I can find male-dominant families to see if the numbers hold up in the next generation. Just too lazy to look at published family trees.

    • In reply to #15 by DStowens:

      Well, the title got me to look at the article – so, I suppose it succeeded. But, as noted by everyone, there wasn’t any choice involved. And there wasn’t any information pertinent to natural selection or evolution or any such thing – it was all observations of zoo animals. They did observe that t…

      I disagree that just because research uses data at a zoo its no longer applicable to natural selection. Of course what goes on in a zoo can’t be considered a model for what happens in an uncontrolled environment but that doesn’t at all mean it can’t give us information on natural selection. In some ways you could say that no experiment really happens “in the wild” the essence of any experiment is that you need to control various factors and by doing that you are by definition doing something different than what would happen in the wild. I also don’t agree that there is something wrong with the research. There may be but no one that I’ve read has pointed out any glaring problems IMO. The issues are with the science writing not the researchers, a very, very common problem unfortunately.

Leave a Reply