page_title: Sexual dimorphism
section_title: Mammals
hierarchical_section_title: Sexual dimorphism / Mammals
caption_attribution_description: Male and female Northern Elephant Seals(Mirounga angustirostris), ,California
context_page_description: Sexual dimorphism is the condition where the two sexes of the same species exhibit different characteristics beyond the differences in their sexual organs. The condition occurs in many animals and some plants. Differences may include secondary sex characteristics, size, weight, colour, markings, and may also include behavioral and cognitive differences. These differences may be subtle or exaggerated, and may be subjected to sexual selection and natural selection. The opposite of dimorphism is monomorphism.
context_section_description: In a large proportion of mammal species, males are larger than females. Both genes and hormones affect the formation of many animal brains before "birth" (or hatching), and also behaviour of adult individuals. Hormones significantly affect human brain formation, and also brain development at puberty. A 2004 review in Nature Reviews Neuroscience observed that "because it is easier to manipulate hormone levels than the expression of sex chromosome genes, the effects of hormones have been studied much more extensively, and are much better understood, than the direct actions in the brain of sex chromosome genes." It concluded that while "the differentiating effects of gonadal secretions seem to be dominant," the existing body of research "support the idea that sex differences in neural expression of X and Y genes significantly contribute to sex differences in brain functions and disease."
caption: Male and female northern elephant seal, the male being larger with a big proboscis
exif: {"Image Make": "Canon", "Image Model": "Canon EOS DIGITAL REBEL XTi", "Image Orientation": "Horizontal (normal)", "Image XResolution": "72", "Image YResolution": "72", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop Elements 2.0", "Image DateTime": "2008:01:16 06:49:53", "Image YCbCrPositioning": "Co-sited", "Image ExifOffset": "236", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "1018", "Thumbnail JPEGInterchangeFormatLength": "5756", "EXIF ExposureTime": "1/1250", "EXIF FNumber": "5", "EXIF ExposureProgram": "Program Action", "EXIF ISOSpeedRatings": "400", "EXIF ExifVersion": "0221", "EXIF DateTimeOriginal": "2008:01:15 14:15:51", "EXIF DateTimeDigitized": "2008:01:15 14:15:51", "EXIF ComponentsConfiguration": "YCbCr", "EXIF ShutterSpeedValue": "84277/8192", "EXIF ApertureValue": "76085/16384", "EXIF ExposureBiasValue": "0", "EXIF MeteringMode": "Pattern", "EXIF Flash": "Flash did not fire, compulsory flash mode", "EXIF FocalLength": "170", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "2616", "EXIF ExifImageLength": "2592", "EXIF FocalPlaneXResolution": "3888000/877", "EXIF FocalPlaneYResolution": "432000/97", "EXIF FocalPlaneResolutionUnit": "2", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF SceneCaptureType": "Standard"}