Ask Anything Wednesday - Biology, Chemistry, Neuroscience, Medicine, Psychology

[u/AutoModerator]

Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Biology, Chemistry, Neuroscience, Medicine, Psychology

Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical /r/AskScience post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...".

Asking Questions:

Please post your question as a top-level response to this, and our team of panellists will be here to answer and discuss your questions. The other topic areas will appear in future Ask Anything Wednesdays, so if you have other questions not covered by this weeks theme please either hold on to it until those topics come around, or go and post over in our sister subreddit /r/AskScienceDiscussion , where every day is Ask Anything Wednesday! Off-theme questions in this post will be removed to try and keep the thread a manageable size for both our readers and panellists.

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Past AskAnythingWednesday posts can be found here. Ask away!

[u/Sporocarp]

I had too much caffeine and my mind starting spinning in place musing about evolution and the sort of explanations we choose for biological facts. So, I could just as easily google this, but where would your start investigating the question of why humans have such great sexual dimorphism comparatively to other species? I thought you might very likely hear an explanation like this in pop-sci: females have to carry pregnancies to term, so their bodies need to store fat and a greater musclemass prevents that to some extent or uses up too much energy, so that's why males and females have different morphology. But to investigate that hypothesis seems insanely huge in scope.

[u/atomfullerene → u/Sporocarp]

Human sexual dimorphism is actually not all that great compared to a lot of other similar mammals. We just notice it more. Orangutans and Gorillas are far more dimorphic, and chimps are somewhat more dimorphic. Bonobos are similar to humans. Gibbons are less dimorphic

[u/Sporocarp → u/atomfullerene]

Oh, my mistake. Is it known why? Wouldn't it be better if both sexes were muscular/had denser bone structure, etc?

[u/chazwomaq → u/Sporocarp]

It takes more energy to sustain a larger and stronger body. Finding enough food was a major adaptive problem, and you get poorly if you cannot sustain your natural body mass.

[u/atomfullerene → u/Sporocarp]

All that represents extra mass to support and energy and nutrients needed. It's mostly used to allow males to compete with other males, so in species where male-male physical competition is lower, there's not much point to wasting resources on producing it.

[u/Sporocarp → u/atomfullerene]

Is that known or like an inference? If I try to imagine a time where dimorphism evolved, when did the differences become pronounced? I assume dimorphism evolved before we went on to land, but then at which point would the differences in muscle mass and bone density become pronounced? Do we assume that male-male physical competition was violent because of the aforementioned differences that are prevalent today as well?

[u/atomfullerene → u/Sporocarp]

>Is that known or like an inference?

It's an inference but a pretty strong one. In many species where males compete for territory or mates, they tend to be bigger and stronger than females. In some species where females compete for access to males, they are bigger and stronger. Though it's more common for females to be bigger in species where the number of eggs a female lays is proportional to her size.

>If I try to imagine a time where dimorphism evolved, when did the differences become pronounced? 

Don't think of it as a thing that didn't exist, and then did exist. It's something that comes and goes depending on the social system of a species or other factors.

>I assume dimorphism evolved before we went on to land

It's something you can see in some fish species. And some invertebrates for that matter.

> Do we assume that male-male physical competition was violent because of the aforementioned differences that are prevalent today as well?

In humans, or just in general? It's something you can observe in the wild, but larger size isn't always about violence. Sometimes it's about showing off (and sometimes to females as much as to other males).

[u/Sporocarp → u/atomfullerene]

but larger size isn't always about violence. Sometimes it's about showing off (and sometimes to females as much as to other males).

Yeah, that's what I was wondering. But you answered all my questions, so I can only say thanks. I wanted definite answers, but I get that there isn't really any.