{"id":62218,"date":"2026-03-24T21:06:41","date_gmt":"2026-03-24T12:06:41","guid":{"rendered":"https:\/\/www.ag.kagawa-u.ac.jp\/?p=62218"},"modified":"2026-04-27T09:00:42","modified_gmt":"2026-04-27T00:00:42","slug":"%e9%80%b2%e5%8c%96%e7%94%9f%e7%89%a9%e5%ad%a6%e6%9c%80%e5%a4%a7%e3%81%ae%e8%ac%8e%e3%80%8c%e6%80%a7%e3%81%ae2%e5%80%8d%e3%81%ae%e3%82%b3%e3%82%b9%e3%83%88%e3%80%8d%e3%81%ab%e7%ad%94%e3%81%88%e3%81%8c","status":"publish","type":"post","link":"https:\/\/www.ag.kagawa-u.ac.jp\/?p=62218","title":{"rendered":"\u9032\u5316\u751f\u7269\u5b66\u6700\u5927\u306e\u8b0e\u300c\u6027\u306e2\u500d\u306e\u30b3\u30b9\u30c8\u300d\u306b\u7b54\u3048\u304c\u5f97\u3089\u308c\u305f"},"content":{"rendered":"\n

\u30d7\u30ec\u30b9\u30ea\u30ea\u30fc\u30b9 Press Release (English follows Japanese)
\u9032\u5316\u751f\u7269\u5b66\u6700\u5927\u306e\u8b0e\u300c\u6027\u306e2\u500d\u306e\u30b3\u30b9\u30c8\u300d\u306b\u7b54\u3048\u304c\u5f97\u3089\u308c\u305f
Answer Found to the Greatest Mystery in Evolutionary Biology: \u201cThe Twofold Cost of Sex\u201d<\/p>\n\n\n\n\n\n

\u539f\u8457\u8ad6\u6587:<\/p>\n\n\n\n

Yukio Yasui, Double-income anisogamy offsets the twofold cost of sex by resource defense. Journal of Ethology<\/em>. March 18, 2026. DOI: 10.1007\/s10164-026-00885-9<\/p>\n\n\n\n

https:\/\/link.springer.com\/article\/10.1007\/s10164-026-00885-9<\/a><\/p>\n\n\n\n

\u5b89\u4e95 \u884c\u96c4\u300c\u8cc7\u6e90\u9632\u885b\u306b\u3088\u3063\u3066\u6027\u306e2\u500d\u306e\u30b3\u30b9\u30c8\u3092\u76f8\u6bba\u3059\u308b\u4e8c\u91cd\u53ce\u5165\u30a2\u30cb\u30bd\u30ac\u30df\u30fc\u300d<\/p>\n\n\n\n

\u307b\u3068\u3093\u3069\u306e\u591a\u7d30\u80de\u751f\u7269\u306f\u30a2\u30cb\u30bd\u30ac\u30df\u30fcanisogamy\u3068\u3044\u3046\u3001\u5927\u304d\u306a\u5375\u3092\u5c0f\u3055\u306a\u7cbe\u5b50\u304c\u53d7\u7cbe\u3059\u308b\u5f62\u306e\u6709\u6027\u751f\u6b96\u3092\u884c\u3044\u307e\u3059\u3002\u3053\u308c\u306f\u540c\u6642\u306b\u5375\u3092\u4f5c\u308b\u96cc\u3068\u7cbe\u5b50\u3092\u4f5c\u308b\u96c4\u306b\u6027\u5225\u304c\u4e8c\u6975\u5316\u3057\u3066\u3044\u308b\u3053\u3068\u3092\u610f\u5473\u3057\u307e\u3059\u3002\u306a\u305c\u96c4\u3068\u96cc\u304c\u3044\u308b\u306e\u304b\u3001\u3053\u308c\u306f\u53e4\u4ee3\u30ae\u30ea\u30b7\u30a2\u306e\u54f2\u4eba\u30a2\u30ea\u30b9\u30c8\u30c6\u30ec\u30b9\u4ee5\u6765\u4e8c\u5343\u5e74\u306b\u308f\u305f\u308b\u4eba\u985e\u306e\u7591\u554f\u3068\u3055\u308c\u3066\u304d\u307e\u3057\u305f\u3002(\u306a\u304a\u672c\u7a3f\u3067\u7528\u3044\u308b\u300c\u96c4\u300d\u300c\u96cc\u300d\u300c\u6027\u5225\u300d\u306a\u3069\u306e\u7528\u8a9e\u306f\u3001\u751f\u7269\u5b66\u306b\u304a\u3051\u308b\u914d\u5076\u5b50\u306e\u6027\u8cea\u306b\u57fa\u3065\u304f\u751f\u7269\u5b66\u7684\u6027\uff08sex\uff09\u3092\u6307\u3059\u5b66\u8853\u7528\u8a9e\u3067\u3042\u308a\u3001\u4eba\u9593\u793e\u4f1a\u306b\u304a\u3051\u308b\u6027\u81ea\u8a8d\u30fb\u793e\u4f1a\u7684\u5f79\u5272\u30fb\u6587\u5316\u7684\u6982\u5ff5\u3068\u3057\u3066\u306e\u30b8\u30a7\u30f3\u30c0\u30fc\uff08gender\uff09\u3084\u500b\u4eba\u306e\u3042\u308a\u65b9\u3092\u793a\u3059\u3082\u306e\u3067\u306f\u3042\u308a\u307e\u305b\u3093\u3002\u307e\u305f\u3001\u672c\u7a3f\u4e2d\u306e\u4eba\u9593\u793e\u4f1a\u3078\u306e\u8a00\u53ca\u3084\u6bd4\u55a9\u306f\u7406\u89e3\u3092\u52a9\u3051\u308b\u305f\u3081\u306e\u8aac\u660e\u4e0a\u306e\u8868\u73fe\u3067\u3042\u308a\u3001\u7279\u5b9a\u306e\u5bb6\u65cf\u5f62\u614b\u30fb\u793e\u4f1a\u5236\u5ea6\u30fb\u4fa1\u5024\u89b3\u3092\u8a55\u4fa1\u307e\u305f\u306f\u898f\u7bc4\u5316\u3059\u308b\u610f\u56f3\u306f\u3042\u308a\u307e\u305b\u3093\u3002)
<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

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\u300c\u6027\u306e2\u500d\u306e\u30b3\u30b9\u30c8\u300d\u3092\u8ad6\u3058\u308b\u3046\u3048\u3067\u91cd\u8981\u306a\u306e\u306f\u3001\u30bb\u30ea\u30c8\u30ad\u30fc\u3068\u30a2\u30cb\u30bd\u30ac\u30df\u30fc\u306e\u500b\u4f53\u7fa4\u5897\u52a0\u7387\u306e\u5dee\u306f\u6bce\u4e16\u4ee32\u500d<\/strong>\u3067\u3042\u308b\u305f\u3081\u300110\u4e16\u4ee3\u5f8c\u306b\u306f\u500b\u4f53\u6570\u306e\u5dee\u306f210<\/sup> = 1024\u500d\u306b\u7d2f\u7a4d\u3055\u308c\u308b\u70b9\u3067\u3059\u3002\u3053\u306e\u3053\u3068\u306f\u30a2\u30cb\u30bd\u30ac\u30df\u30fc\u304c\u30bb\u30ea\u30c8\u30ad\u30fc\u306b\u5bfe\u6297\u3057\u3088\u3046\u3068\u3059\u308c\u3070\u3001\u96c4\u304c\u6bce\u4e16\u4ee32\u500d\u306e\u5229\u76ca\u3092\u3082\u305f\u3089\u3055\u306a\u3051\u308c\u3070\u63a1\u7b97\u304c\u5408\u308f\u306a\u3044\u3053\u3068\u3092\u610f\u5473\u3057\u307e\u3059\u3002\u3057\u305f\u304c\u3063\u3066\u96c4\u304b\u3089\u6765\u308b\u3068\u671f\u5f85\u3055\u308c\u308b\u5229\u76ca\u306f\u5f8c\u306e\u4e16\u4ee3\u306b\u9045\u308c\u3066\u623b\u3063\u3066\u304f\u308b\u3088\u3046\u306a\u300c\u907a\u4f1d\u7684\u5229\u76ca\u300d\u3067\u306f\u3068\u3066\u3082\u9593\u306b\u5408\u3044\u307e\u305b\u3093\u3002\u305f\u3068\u3048\u3070\u73fe\u5728\u6709\u6027\u751f\u6b96\u306e\u5229\u76ca\u3068\u3057\u3066\u5b9a\u756a\u7406\u8ad6\u3068\u306a\u3063\u3066\u3044\u308b\u300c\u8d64\u306e\u5973\u738b\u300d\u4eee\u8aac\u3067\u306f\u3001\u96c4\u304c\u96cc\u3068\u306f\u7570\u306a\u308b\u907a\u4f1d\u5b50\u3092\u6301\u3061\u3001\u4ea4\u914d\u306b\u3088\u3063\u3066\u65b0\u305f\u306a\u9069\u5fdc\u7684\u907a\u4f1d\u5b50\u578b\uff08\u75c5\u539f\u62b5\u6297\u6027\u306a\u3069\uff09\u304c\u751f\u307f\u51fa\u3055\u308c\u308b\u3068\u60f3\u5b9a\u3057\u3066\u3044\u307e\u3059\u304c\u3001\u6027\u81ea\u4f53\u306f\u65b0\u305f\u306a\u7a81\u7136\u5909\u7570\u3092\u751f\u307f\u51fa\u3059\u308f\u3051\u3067\u306f\u306a\u304f\u305d\u306e\u7d44\u307f\u5408\u308f\u305b\u3092\u30e9\u30f3\u30c0\u30e0\u306b\u5909\u3048\u3066\u3044\u308b\u3060\u3051\u306a\u306e\u3067\u3001\u74b0\u5883\u304c\u523b\u3005\u5909\u5316\u3057\u3066\u512a\u52e2\u306a\u75c5\u539f\u4f53\u306e\u7a2e\u985e\u3082\u4e16\u4ee3\u9593\u3067\u79fb\u308a\u5909\u308f\u308b\u3068\u304d\u3001\u305d\u308c\u306b\u3046\u307e\u304f\u5bfe\u5fdc\u3067\u304d\u308b\u907a\u4f1d\u5b50\u578b\u3092\u6bce\u4e16\u4ee3\u4f5c\u308a\u7d9a\u3051\u308b<\/strong>\u3053\u3068\u306a\u3069\u4e0d\u53ef\u80fd\u3067\u3059\u3002\u30a2\u30cb\u30bd\u30ac\u30df\u30fc\u96c6\u56e3\u3092\u30bb\u30ea\u30c8\u30ad\u30fc\u7a81\u7136\u5909\u7570\u4f53\u306e\u4fb5\u5165\u304b\u3089\u5b88\u308b\u305f\u3081\u306b\u306f\u5f8c\u8005\u304c\u751f\u3058\u305f\u305d\u306e\u90fd\u5ea6\u3001\u305d\u308c\u3092\u6bba\u3055\u306a\u3051\u308c\u3070\u306a\u308a\u307e\u305b\u3093\u3002\u96c4\u7531\u6765\u306e\u300c2\u500d\u306e\u5229\u76ca\u300d\u304c\u306a\u3051\u308c\u3070\u30a2\u30cb\u30bd\u30ac\u30df\u30fc\u306f\u30bb\u30ea\u30c8\u30ad\u30fc\u306b\u52dd\u3066\u305a\u3001\u7af6\u4e89\u304c\u6b21\u4e16\u4ee3\u306b\u6301\u3061\u8d8a\u3055\u308c\u308b\u3068\u3001\u30bb\u30ea\u30c8\u30ad\u30fc\u306e\u500b\u4f53\u6570\u306f\uff12\u500d\u306b\u306a\u308a\u3001\u52dd\u3064\u3053\u3068\u306f\u3055\u3089\u306b\u96e3\u3057\u304f\u306a\u308a\u307e\u3059\u3002\u3057\u305f\u304c\u3063\u3066\u96c4\u304b\u3089\u3082\u305f\u3089\u3055\u308c\u308b\u306e\u306f\u3001\u305d\u306e\u4e16\u4ee3(\u4ea4\u5c3e\u3057\u305f\u96cc\u81ea\u8eab)\u306b\u304a\u3044\u3066\u9069\u5fdc\u5ea6\uff08\u751f\u5b58\u3059\u308b\u5a18\u306e\u6570\uff09\u3092\u5373\u5ea7\u306b2\u500d\u306b\u9ad8\u3081\u308b\uff08\u30bb\u30ea\u30c8\u30ad\u30fc\u3068\u540c\u7b49\u306b\u3059\u308b\uff09\u3088\u3046\u306a\u7269\u8cea\u7684\u5229\u76ca\u3067\u306a\u3051\u308c\u3070\u306a\u3089\u306a\u3044\u3068\u3044\u3046\u3053\u3068\u306b\u306a\u308a\u307e\u3059\u3002<\/p>\n\n\n\n

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<\/p>\n\n\n

\n
\"\"<\/figure>\n<\/div>\n\n\n

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\u672c\u8ad6\u6587\u306b\u52a0\u3048\u3001\u300c\u96c4\u304c\u306a\u305c\u7dad\u6301\u3055\u308c\u308b\u306e\u304b\u300d\u306e\u554f\u984c\u3092\u6e1b\u6570\u5206\u88c2\u306e\u6a5f\u68b0\u7684\u5236\u7d04\u304b\u3089\u8aac\u660e\u3059\u308b\u7b2c3\u8ad6\u6587\u3082\u307e\u3082\u306a\u304f\u516c\u8868\u898b\u8fbc\u307f\uff08\u516c\u8868\u5f8c\u306b\u672c\u30b5\u30a4\u30c8\u306b\u63b2\u8f09\u4e88\u5b9a\uff09\u3068\u306a\u3063\u3066\u3044\u3066\u3001\u3053\u306e\u300c\u6027\u306e\u9032\u53163\u90e8\u4f5c\u300d\u306b\u3088\u3063\u3066\u9032\u5316\u751f\u7269\u5b66\u6700\u5927\u306e\u8b0e\u306f\u89e3\u6c7a\u306b\u5411\u304b\u3046\u3053\u3068\u3068\u306a\u308a\u307e\u3059\u3002<\/p>\n\n\n\n

\u5b89\u4e95\u6559\u6388\u306f\u300c\u3053\u308c\u3089\u306e\u4eee\u8aac\u306f\u4e0d\u5b8c\u5168\u306a\u30e1\u30ab\u30cb\u30ba\u30e0\u3067\u3042\u308a\u3001\u4e0d\u5b8c\u5168\u3060\u304b\u3089\u3053\u305d\u7406\u306b\u304b\u306a\u3063\u305f\u8aac\u660e\u3068\u306a\u308b\u300d\u3068\u8ff0\u3079\u3066\u3044\u307e\u3059\u3002\u3082\u3057\u30c0\u30d6\u30eb\u30a4\u30f3\u30ab\u30e0\u3068\u6e1b\u6570\u5206\u88c2\u306e\u5236\u7d04\u304c\u5b8c\u5168\u306b\u30bb\u30ea\u30c8\u30ad\u30fc\u306e\u4fb5\u5165\u3092\u963b\u6b62\u3067\u304d\u308b\u306e\u3067\u3042\u308c\u3070\u3001\u30bb\u30ea\u30c8\u30ad\u30fc\u306e\u7a2e\u306f\u5b58\u5728\u3057\u306a\u3044\u3053\u3068\u306b\u306a\u308a\u307e\u3059\u3002\u3053\u308c\u3089\u306e\u969c\u58c1\u3092\u7a81\u7834\u3067\u304d\u305f\u3082\u306e\u304c\u3044\u308b\u304b\u3089\u3053\u305d\u5c11\u6570\u6d3e\u306a\u304c\u3089\u30bb\u30ea\u30c8\u30ad\u30fc\u306e\u7a2e\u306f\u5b9f\u5728\u3057\u3001\u96c4\u3092\u4f5c\u3089\u306a\u30442\u500d\u306e\u6709\u5229\u6027\u306b\u3088\u3063\u3066\u77ed\u671f\u7684\u306b\u306f\u7e41\u6804\u3059\u308b\u304c\u907a\u4f1d\u7684\u591a\u69d8\u6027\u3092\u5931\u3046\u305f\u3081\uff08\u3053\u3053\u3067\u300c\u8d64\u306e\u5973\u738b\u300d\u7b49\u306e\u5f93\u6765\u4eee\u8aac\u304c\u91cd\u8981\u3068\u306a\u308b\uff09\u3001\u4e2d\u9577\u671f\u7684\u306b\u306f\u7d76\u6ec5\u306b\u5411\u304b\u3044\u3001\u5927\u534a\u306e\u591a\u7d30\u80de\u52d5\u7269\u306f\u96c4\u3068\u96cc\u3092\u6301\u3061\u3001\u4e00\u90e8\u306b\u96cc\u3060\u3051\u306e\u7a2e\u304c\u3044\u308b\u3068\u3044\u3046\u81ea\u7136\u754c\u306e\u73fe\u72b6\u304c\u8aac\u660e\u3055\u308c\u308b\u3053\u3068\u306b\u306a\u308b\u306e\u3067\u3059\u3002\u6700\u5f8c\u306b\u5b89\u4e95\u6559\u6388\u306f\u8ff0\u3079\u3066\u3044\u307e\u3059\u3002\u300c\u9032\u5316\u751f\u7269\u5b66\u306e\u5b9a\u8aac\u3067\u306f\u3001\u96c4\u306f\u96cc\u306b\u5bfe\u3059\u308b\u5bc4\u751f\u8005\u3067\u3042\u308b\u3068\u8003\u3048\u3089\u308c\u3066\u304d\u305f\u3002\u3057\u304b\u3057\u5bc4\u751f\u8005\u304c\u5bc4\u4e3b\u3068\u540c\u6570\u5b58\u5728\u3059\u308b\u30b7\u30b9\u30c6\u30e0\u304c\u306f\u305f\u3057\u3066\u5b89\u5b9a\u3067\u3044\u3089\u308c\u308b\u3060\u308d\u3046\u304b\u3002\u96c4\u306f\u96cc\u3092\u901a\u3058\u3066\u3057\u304b\u7e41\u6b96\u3067\u304d\u306a\u3044\u306e\u3067\u96cc\u306b\u5354\u529b\u305b\u3056\u308b\u3092\u5f97\u306a\u3044\u3002\u305f\u3068\u3048\u5171\u9032\u5316\u306e\u904e\u7a0b\u3067\u4e00\u6642\u7684\u306b\u5bfe\u7acb\u95a2\u4fc2\u304c\u751f\u3058\u308b\u3068\u3057\u3066\u3082\u7a76\u6975\u7684\u306b\u306f\u96c4\u3068\u96cc\u306f\u76f8\u5229\u5171\u751f\u95a2\u4fc2\u306b\u3042\u308b\u306e\u3067\u3042\u308b\u3002\u300d<\/p>\n\n\n\n

Answer Found to the Greatest Mystery in Evolutionary Biology: \u201cThe Twofold Cost of Sex\u201d<\/p>\n\n\n\n

Original Paper:<\/p>\n\n\n\n

Yukio Yasui, Double-income anisogamy offsets the twofold cost of sex by resource defense. Journal of Ethology<\/em>. 44:189\u2013206. March 18, 2026. DOI: 10.1007\/s10164-026-00885-9 https:\/\/link.springer.com\/article\/10.1007\/s10164-026-00885-9<\/a><\/p>\n\n\n\n

Most multicellular organisms reproduce sexually through a process called anisogamy, in which large eggs are fertilized by small sperm. This implies that sex is polarized into males, who produce sperm, and females, who produce eggs. Why there are males and females has been a question that has puzzled humanity for two thousand years, ever since the ancient Greek philosopher Aristotle. (Note that terms such as \u201cmale,\u201d \u201cfemale,\u201d and \u201csex\u201d used in this document refer to biological sex\u2014a scientific term based on the characteristics of gametes in biology\u2014and do not refer to gender as a concept of sexual identity, social roles, or cultural perspectives within human society, nor do they describe an individual\u2019s personal identity. Furthermore, references to human society and metaphors used in this document are for illustrative purposes to aid understanding and are not intended to evaluate or standardize specific family structures, social systems, or values.)
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In anisogamy, half of the offspring produced by a mother are males, who do not reproduce themselves. If an asexual thelytoky female\u2014one that produces only females due to a mutation\u2014were to arise in an anisogamous population, her reproduction rate would be twofold compared to anisogamy, so it is expected that she would replace the sexual population within a few generations. This overwhelming disadvantage associated with sexual reproduction is referred to as the \u201ctwofold cost of sex\u201d or the \u201ccost of producing males.\u201d The fact that males are maintained in most species despite the disadvantage is one of the greatest mysteries in evolutionary biology. Since the 20th century, numerous geniuses\u2014including Herman J. Muller, John Maynard-Smith, Geoffrey A. Parker, and William D. Hamilton\u2014have tackled this difficult problem, but their explanations remain incomplete. Professor Dr. Yukio Yasui of the Faculty of Agriculture, Kagawa University, Japan has been working on this problem for many years. In 2022, he astonished the world with his paper \u201cThe origination events of gametic sexual reproduction and anisogamy\u201d (https:\/\/link.springer.com\/article\/10.1007\/s10164-022-00760-3<\/a>), and now he has presented a new theory explaining the ultimate puzzle: \u201cWhy are costly males maintained?\u201d<\/p>\n\n\n\n

An important point in discussing the \u201ctwofold cost of sex\u201d is that, because the difference in population growth rates between thelytoky and anisogamy is twofold per generation<\/strong>, the difference in population size accumulates to 210<\/sup> = 1,024 times after 10 generations. This means that for anisogamy to compete with thelytoky, males must provide twofold benefit per generation for it to be worth the cost. Consequently, the benefits expected from males cannot possibly be met by \u201cgenetic benefits\u201d that return only in later generations. For example, the \u201cRed Queen\u201d hypothesis\u2014which is currently a standard theory regarding the benefits of sexual reproduction\u2014 assumes that males carry different genes from females and that mating produces new adaptive genotypes (such as pathogen resistance). However, because sex itself does not generate new mutations but merely randomly recombines existing ones, it is impossible to continue producing genotypes capable of successfully adapting to the environment when it changes moment by moment and the dominant pathogen types shift from generation to generation. To protect an anisogamous population from the invasion of thelytokous mutants, the latter must be eliminated each time they arise. Without the \u201ctwofold benefit\u201d derived from males, anisogamy cannot prevail over thelytoky; if the competition carries over to the next generation, the thelytoky population will double, making victory even more difficult. Therefore, what the male must provide is a material benefit that immediately achieves a twofold increase in fitness (number of surviving daughters) in that generation (for the mated female herself), equalling that of thelytoky.<\/p>\n\n\n\n

However, in many animal species, males devote their energy almost exclusively to increasing the frequency of mating, and only a limited number of species involve males in feeding females or caring for offspring (birds and humans are, in fact, exceptions). Nevertheless, \u201cresource defense\u201d\u2014where males protect resources that are important to females and offspring as part of their reproductive strategy\u2014is widely observed. Professor Yasui has theoretically linked \u201cmale resource defense\u201d\u2014which was previously considered unrelated to the \u201ctwofold cost of males\u201d problem\u2014to this phenomenon. Males secure abundant food sources and safe breeding sites, granting access to these resources only to sexually receptive females. On the other hand, asexual females do not accept mating and are therefore excluded by males, thus unable to obtain resources. As a result, while asexual females remain in a \u201csingle-income\u201d state based solely on resources they acquire themselves (which Professor Yasui termed the \u201ctwofold cost of being single\u201d), sexual females enter a \u201cdouble-income\u201d state that combines their own resources with those provided by males. Even if the resources secured by males are not utilized by females 100% efficiently, if females use the additional resources to improve the survival rate of existing eggs rather than for additional egg production, they can achieve a fitness (number of surviving daughters) equal to or greater than that of thelytoky. Mathematical models and simulations demonstrate that this mechanism can actually overcome the \u201ctwofold cost of sex.\u201d
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This hypothesis is simple and intuitive enough for anyone to understand. It is generally known that offspring survival is greater under biparental care than under uniparental care. In the natural world, too, a relationship has been demonstrated between resource defense by males and reproductive success in females across many species, ranging from insects to fish, amphibians, birds, mammals, and humans. Inspired by this research, empirical studies are advancing, and it is expected that there will be an increase in reports showing that even when males do not directly provide food to their partners, they still confer significant benefits on mothers and offspring by defending valuable territories.<\/p>\n\n\n\n

In addition to this paper, a third paper explaining why males persist based on the mechanical constraints of meiosis is expected to be published shortly (and will be posted on this site once published); with this \u201cTrilogy on the Evolution of Sex,\u201d one of the greatest mysteries in evolutionary biology will be on the verge of being solved.<\/p>\n\n\n\n

Professor Yasui states, \u201cThese hypotheses represent incomplete mechanisms, and it is precisely because they are incomplete that they provide a plausible explanation.\u201d If the double-income and meiotic constraints were capable of completely preventing the invasion of thelytoky, then thelytokous species would not exist. It is precisely because some species have managed to overcome these barriers that thelytoky species\u2014though a minority\u2014actually exist. Although they prosper in the short term due to the twofold advantage of not producing males, they lose genetic diversity (which is where conventional hypotheses such as the \u201cRed Queen\u201d theory become important). Consequently, they face extinction in the medium to long term. This explains the current state of nature, where most multicellular animals possess both males and females, while a small number of species consist solely of females. Finally, Professor Yasui states: \u201cIn traditional evolutionary biology, males have been considered parasites of females. However, can a system in which the number of parasites equals that of the hosts truly remain evolutionarily stable? Because males can reproduce only through females, they have no choice to cooperate with them. Even if a temporary antagonistic relationship arises during the process of coevolution, ultimately, males and females exist in a mutually beneficial symbiotic relationship.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"

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