How did the human thumb develop? Why are humans the only mammals with thumbs? <\/p>\n\n\n\n
The human thumb is one of the most significant reasons that humans were able to develop and evolve in the way we did. In Your Inner Fish<\/em> by Neil Shubin, he argues that the human thumb is a part of our development from fish. <\/p>\n\n\n\n Read more about the human thumb and how it developed from our ocean ancestors. <\/p>\n\n\n\n\n\n\n\n Just as echoes of our bone development can be seen in earlier animals, our genetic recipe also traces back to other creatures.<\/strong> DNA research answers questions about our development that fossil study can\u2019t answer because variables can be manipulated in animal embryos to see what happens.<\/p>\n\n\n\n DNA contains the \u201crecipe\u201d that builds human or animal bodies from an egg. By experimenting with DNA in animal and shark embryos, scientists have shown that all appendages, whether limbs or fins, develop the same way from the same DNA recipe<\/strong>. This chapter looks at the experiments, starting in the fifties and sixties, that led to this understanding.<\/p>\n\n\n\n Although the human body is made up of hundreds of different kinds of cells, which make our bones, organs, nerves, and tissues function differently, all cells contain the same DNA. <\/p>\n\n\n\n Organ and tissue cells develop differently because certain genes (stretches of DNA) in the cells are active while others are turned off. The active genes make a protein affecting what a cell looks like and how it behaves.<\/p>\n\n\n\n Understanding the on-off mechanism explains what genes build which parts of the body and how they work, whether building a limb or a fin.<\/p>\n\n\n\n Our hands are three dimensional, with a top\/bottom, thumb side\/little finger side, and base\/tip. Understanding the genes that make the human thumb different from the little finger or fingers different from arm bones is a key to the genetic recipe that builds hands and the rest of our bodies.<\/p>\n\n\n\n In an embryo, the genetic switches for forming limbs activate between the third and eighth week after conception and limbs start developing. First, tiny buds protrude from the embryonic body, then the tips develop into paddles. The paddles contain millions of cells that ultimately become the limb\u2019s skeleton, nerves, and muscles. <\/p>\n\n\n\n To learn about the process, scientists experiment with genetic mutations that make limbs malform. In the fifties and sixties, scientists experimenting with chicken embryos uncovered a key mechanism\u2014a patch of tissue\u2014that controls development of the bone pattern of limbs. By removing the patch, they could stop limb development at various points.<\/strong> They called the patch, which causes the little-finger side of a hand to differentiate from the human thumb side, the ZPA, or zone of polarizing activity.<\/p>\n\n\n\n Moving the ZPA from the little-finger side of the limb bud to the human thumb side caused the embryo to develop a duplicate set of digits mirroring the normal set on that side.<\/p>\n\n\n\n The ZPA controls development of fingers and toes by varying the concentration of a molecule in the cells building the limb. The cells nearest to the ZPA have a high concentration of the molecule and make a little finger. The cells farther away from the ZPA have a lower concentration of the molecule and make a thumb. The cells in between have varying concentrations and make second, third, and fourth fingers.<\/p>\n","protected":false},"excerpt":{"rendered":" How did the human thumb develop? Why are humans the only mammals with thumbs? The human thumb is one of the most significant reasons that humans were able to develop and evolve in the way we did. In Your Inner Fish by Neil Shubin, he argues that the human thumb is a part of our development from fish. Read more about the human thumb and how it developed from our ocean ancestors.<\/p>\n","protected":false},"author":5,"featured_media":17584,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[15],"tags":[149],"class_list":["post-17559","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-education","tag-your-inner-fish","","tg-column-two"],"yoast_head":"\nHow Genes Develop Limbs<\/strong> and The Formation of the Human Thumb<\/h2>\n\n\n\n
Forming Hands<\/strong> and Thumbs<\/h3>\n\n\n\n